zte's code,first commit
Change-Id: I9a04da59e459a9bc0d67f101f700d9d7dc8d681b
diff --git a/ap/os/linux/linux-3.4.x/net/ipv4/tcp_input.c b/ap/os/linux/linux-3.4.x/net/ipv4/tcp_input.c
new file mode 100755
index 0000000..924af66
--- /dev/null
+++ b/ap/os/linux/linux-3.4.x/net/ipv4/tcp_input.c
@@ -0,0 +1,6151 @@
+/*
+ * INET An implementation of the TCP/IP protocol suite for the LINUX
+ * operating system. INET is implemented using the BSD Socket
+ * interface as the means of communication with the user level.
+ *
+ * Implementation of the Transmission Control Protocol(TCP).
+ *
+ * Authors: Ross Biro
+ * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
+ * Mark Evans, <evansmp@uhura.aston.ac.uk>
+ * Corey Minyard <wf-rch!minyard@relay.EU.net>
+ * Florian La Roche, <flla@stud.uni-sb.de>
+ * Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
+ * Linus Torvalds, <torvalds@cs.helsinki.fi>
+ * Alan Cox, <gw4pts@gw4pts.ampr.org>
+ * Matthew Dillon, <dillon@apollo.west.oic.com>
+ * Arnt Gulbrandsen, <agulbra@nvg.unit.no>
+ * Jorge Cwik, <jorge@laser.satlink.net>
+ */
+
+/*
+ * Changes:
+ * Pedro Roque : Fast Retransmit/Recovery.
+ * Two receive queues.
+ * Retransmit queue handled by TCP.
+ * Better retransmit timer handling.
+ * New congestion avoidance.
+ * Header prediction.
+ * Variable renaming.
+ *
+ * Eric : Fast Retransmit.
+ * Randy Scott : MSS option defines.
+ * Eric Schenk : Fixes to slow start algorithm.
+ * Eric Schenk : Yet another double ACK bug.
+ * Eric Schenk : Delayed ACK bug fixes.
+ * Eric Schenk : Floyd style fast retrans war avoidance.
+ * David S. Miller : Don't allow zero congestion window.
+ * Eric Schenk : Fix retransmitter so that it sends
+ * next packet on ack of previous packet.
+ * Andi Kleen : Moved open_request checking here
+ * and process RSTs for open_requests.
+ * Andi Kleen : Better prune_queue, and other fixes.
+ * Andrey Savochkin: Fix RTT measurements in the presence of
+ * timestamps.
+ * Andrey Savochkin: Check sequence numbers correctly when
+ * removing SACKs due to in sequence incoming
+ * data segments.
+ * Andi Kleen: Make sure we never ack data there is not
+ * enough room for. Also make this condition
+ * a fatal error if it might still happen.
+ * Andi Kleen: Add tcp_measure_rcv_mss to make
+ * connections with MSS<min(MTU,ann. MSS)
+ * work without delayed acks.
+ * Andi Kleen: Process packets with PSH set in the
+ * fast path.
+ * J Hadi Salim: ECN support
+ * Andrei Gurtov,
+ * Pasi Sarolahti,
+ * Panu Kuhlberg: Experimental audit of TCP (re)transmission
+ * engine. Lots of bugs are found.
+ * Pasi Sarolahti: F-RTO for dealing with spurious RTOs
+ */
+
+#define pr_fmt(fmt) "TCP: " fmt
+
+#include <linux/mm.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+#include <linux/sysctl.h>
+#include <linux/kernel.h>
+#include <net/dst.h>
+#include <net/tcp.h>
+#include <net/inet_common.h>
+#include <linux/ipsec.h>
+#include <asm/unaligned.h>
+#include <net/netdma.h>
+#include <net/SI/errno_track.h>
+#include <net/SI/sock_track.h>
+
+
+int sysctl_tcp_timestamps __read_mostly = 1;
+int sysctl_tcp_window_scaling __read_mostly = 1;
+int sysctl_tcp_sack __read_mostly = 1;
+int sysctl_tcp_fack __read_mostly = 1;
+int sysctl_tcp_reordering __read_mostly = TCP_FASTRETRANS_THRESH;
+EXPORT_SYMBOL(sysctl_tcp_reordering);
+int sysctl_tcp_ecn __read_mostly = 2;
+EXPORT_SYMBOL(sysctl_tcp_ecn);
+int sysctl_tcp_dsack __read_mostly = 1;
+int sysctl_tcp_app_win __read_mostly = 31;
+int sysctl_tcp_adv_win_scale __read_mostly = 1;
+EXPORT_SYMBOL(sysctl_tcp_adv_win_scale);
+
+/* rfc5961 challenge ack rate limiting */
+int sysctl_tcp_challenge_ack_limit = 100;
+
+int sysctl_tcp_stdurg __read_mostly;
+int sysctl_tcp_rfc1337 __read_mostly;
+int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
+int sysctl_tcp_frto __read_mostly = 2;
+int sysctl_tcp_frto_response __read_mostly;
+int sysctl_tcp_nometrics_save __read_mostly;
+
+int sysctl_tcp_thin_dupack __read_mostly;
+
+int sysctl_tcp_moderate_rcvbuf __read_mostly = 1;
+int sysctl_tcp_abc __read_mostly;
+
+#define FLAG_DATA 0x01 /* Incoming frame contained data. */
+#define FLAG_WIN_UPDATE 0x02 /* Incoming ACK was a window update. */
+#define FLAG_DATA_ACKED 0x04 /* This ACK acknowledged new data. */
+#define FLAG_RETRANS_DATA_ACKED 0x08 /* "" "" some of which was retransmitted. */
+#define FLAG_SYN_ACKED 0x10 /* This ACK acknowledged SYN. */
+#define FLAG_DATA_SACKED 0x20 /* New SACK. */
+#define FLAG_ECE 0x40 /* ECE in this ACK */
+#define FLAG_SLOWPATH 0x100 /* Do not skip RFC checks for window update.*/
+#define FLAG_ONLY_ORIG_SACKED 0x200 /* SACKs only non-rexmit sent before RTO */
+#define FLAG_SND_UNA_ADVANCED 0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */
+#define FLAG_DSACKING_ACK 0x800 /* SACK blocks contained D-SACK info */
+#define FLAG_NONHEAD_RETRANS_ACKED 0x1000 /* Non-head rexmitted data was ACKed */
+#define FLAG_SACK_RENEGING 0x2000 /* snd_una advanced to a sacked seq */
+#define FLAG_UPDATE_TS_RECENT 0x4000 /* tcp_replace_ts_recent() */
+
+#define FLAG_ACKED (FLAG_DATA_ACKED|FLAG_SYN_ACKED)
+#define FLAG_NOT_DUP (FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
+#define FLAG_CA_ALERT (FLAG_DATA_SACKED|FLAG_ECE)
+#define FLAG_FORWARD_PROGRESS (FLAG_ACKED|FLAG_DATA_SACKED)
+#define FLAG_ANY_PROGRESS (FLAG_FORWARD_PROGRESS|FLAG_SND_UNA_ADVANCED)
+
+#define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
+#define TCP_HP_BITS (~(TCP_RESERVED_BITS|TCP_FLAG_PSH))
+
+/* Adapt the MSS value used to make delayed ack decision to the
+ * real world.
+ */
+static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb)
+{
+ struct inet_connection_sock *icsk = inet_csk(sk);
+ const unsigned int lss = icsk->icsk_ack.last_seg_size;
+ unsigned int len;
+
+ icsk->icsk_ack.last_seg_size = 0;
+
+ /* skb->len may jitter because of SACKs, even if peer
+ * sends good full-sized frames.
+ */
+ len = skb_shinfo(skb)->gso_size ? : skb->len;
+ if (len >= icsk->icsk_ack.rcv_mss) {
+ icsk->icsk_ack.rcv_mss = len;
+ } else {
+ /* Otherwise, we make more careful check taking into account,
+ * that SACKs block is variable.
+ *
+ * "len" is invariant segment length, including TCP header.
+ */
+ len += skb->data - skb_transport_header(skb);
+ if (len >= TCP_MSS_DEFAULT + sizeof(struct tcphdr) ||
+ /* If PSH is not set, packet should be
+ * full sized, provided peer TCP is not badly broken.
+ * This observation (if it is correct 8)) allows
+ * to handle super-low mtu links fairly.
+ */
+ (len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
+ !(tcp_flag_word(tcp_hdr(skb)) & TCP_REMNANT))) {
+ /* Subtract also invariant (if peer is RFC compliant),
+ * tcp header plus fixed timestamp option length.
+ * Resulting "len" is MSS free of SACK jitter.
+ */
+ len -= tcp_sk(sk)->tcp_header_len;
+ icsk->icsk_ack.last_seg_size = len;
+ if (len == lss) {
+ icsk->icsk_ack.rcv_mss = len;
+ return;
+ }
+ }
+ if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)
+ icsk->icsk_ack.pending |= ICSK_ACK_PUSHED2;
+ icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
+ }
+}
+
+static void tcp_incr_quickack(struct sock *sk)
+{
+ struct inet_connection_sock *icsk = inet_csk(sk);
+ unsigned quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss);
+
+ if (quickacks == 0)
+ quickacks = 2;
+ if (quickacks > icsk->icsk_ack.quick)
+ icsk->icsk_ack.quick = min(quickacks, TCP_MAX_QUICKACKS);
+}
+
+static void tcp_enter_quickack_mode(struct sock *sk)
+{
+ struct inet_connection_sock *icsk = inet_csk(sk);
+ tcp_incr_quickack(sk);
+ icsk->icsk_ack.pingpong = 0;
+ icsk->icsk_ack.ato = TCP_ATO_MIN;
+}
+
+/* Send ACKs quickly, if "quick" count is not exhausted
+ * and the session is not interactive.
+ */
+
+static inline int tcp_in_quickack_mode(const struct sock *sk)
+{
+ const struct inet_connection_sock *icsk = inet_csk(sk);
+ return icsk->icsk_ack.quick && !icsk->icsk_ack.pingpong;
+}
+
+static inline void TCP_ECN_queue_cwr(struct tcp_sock *tp)
+{
+ if (tp->ecn_flags & TCP_ECN_OK)
+ tp->ecn_flags |= TCP_ECN_QUEUE_CWR;
+}
+
+static inline void TCP_ECN_accept_cwr(struct tcp_sock *tp, const struct sk_buff *skb)
+{
+ if (tcp_hdr(skb)->cwr)
+ tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
+}
+
+static inline void TCP_ECN_withdraw_cwr(struct tcp_sock *tp)
+{
+ tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
+}
+
+static inline void TCP_ECN_check_ce(struct tcp_sock *tp, const struct sk_buff *skb)
+{
+ if (!(tp->ecn_flags & TCP_ECN_OK))
+ return;
+
+ switch (TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK) {
+ case INET_ECN_NOT_ECT:
+ /* Funny extension: if ECT is not set on a segment,
+ * and we already seen ECT on a previous segment,
+ * it is probably a retransmit.
+ */
+ if (tp->ecn_flags & TCP_ECN_SEEN)
+ tcp_enter_quickack_mode((struct sock *)tp);
+ break;
+ case INET_ECN_CE:
+ tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
+ /* fallinto */
+ default:
+ tp->ecn_flags |= TCP_ECN_SEEN;
+ }
+}
+
+static inline void TCP_ECN_rcv_synack(struct tcp_sock *tp, const struct tcphdr *th)
+{
+ if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || th->cwr))
+ tp->ecn_flags &= ~TCP_ECN_OK;
+}
+
+static inline void TCP_ECN_rcv_syn(struct tcp_sock *tp, const struct tcphdr *th)
+{
+ if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || !th->cwr))
+ tp->ecn_flags &= ~TCP_ECN_OK;
+}
+
+static inline int TCP_ECN_rcv_ecn_echo(const struct tcp_sock *tp, const struct tcphdr *th)
+{
+ if (th->ece && !th->syn && (tp->ecn_flags & TCP_ECN_OK))
+ return 1;
+ return 0;
+}
+
+/* Buffer size and advertised window tuning.
+ *
+ * 1. Tuning sk->sk_sndbuf, when connection enters established state.
+ */
+
+static void tcp_fixup_sndbuf(struct sock *sk)
+{
+ int sndmem = SKB_TRUESIZE(tcp_sk(sk)->rx_opt.mss_clamp + MAX_TCP_HEADER);
+
+ sndmem *= TCP_INIT_CWND;
+ if (sk->sk_sndbuf < sndmem)
+ sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]);
+}
+
+/* 2. Tuning advertised window (window_clamp, rcv_ssthresh)
+ *
+ * All tcp_full_space() is split to two parts: "network" buffer, allocated
+ * forward and advertised in receiver window (tp->rcv_wnd) and
+ * "application buffer", required to isolate scheduling/application
+ * latencies from network.
+ * window_clamp is maximal advertised window. It can be less than
+ * tcp_full_space(), in this case tcp_full_space() - window_clamp
+ * is reserved for "application" buffer. The less window_clamp is
+ * the smoother our behaviour from viewpoint of network, but the lower
+ * throughput and the higher sensitivity of the connection to losses. 8)
+ *
+ * rcv_ssthresh is more strict window_clamp used at "slow start"
+ * phase to predict further behaviour of this connection.
+ * It is used for two goals:
+ * - to enforce header prediction at sender, even when application
+ * requires some significant "application buffer". It is check #1.
+ * - to prevent pruning of receive queue because of misprediction
+ * of receiver window. Check #2.
+ *
+ * The scheme does not work when sender sends good segments opening
+ * window and then starts to feed us spaghetti. But it should work
+ * in common situations. Otherwise, we have to rely on queue collapsing.
+ */
+
+/* Slow part of check#2. */
+static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ /* Optimize this! */
+ int truesize = tcp_win_from_space(skb->truesize) >> 1;
+ int window = tcp_win_from_space(sysctl_tcp_rmem[2]) >> 1;
+
+ while (tp->rcv_ssthresh <= window) {
+ if (truesize <= skb->len)
+ return 2 * inet_csk(sk)->icsk_ack.rcv_mss;
+
+ truesize >>= 1;
+ window >>= 1;
+ }
+ return 0;
+}
+
+static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ /* Check #1 */
+ if (tp->rcv_ssthresh < tp->window_clamp &&
+ (int)tp->rcv_ssthresh < tcp_space(sk) &&
+ !sk_under_memory_pressure(sk)) {
+ int incr;
+
+ /* Check #2. Increase window, if skb with such overhead
+ * will fit to rcvbuf in future.
+ */
+ if (tcp_win_from_space(skb->truesize) <= skb->len)
+ incr = 2 * tp->advmss;
+ else
+ incr = __tcp_grow_window(sk, skb);
+
+ if (incr) {
+ incr = max_t(int, incr, 2 * skb->len);
+ tp->rcv_ssthresh = min(tp->rcv_ssthresh + incr,
+ tp->window_clamp);
+ inet_csk(sk)->icsk_ack.quick |= 1;
+ }
+ }
+}
+
+/* 3. Tuning rcvbuf, when connection enters established state. */
+
+static void tcp_fixup_rcvbuf(struct sock *sk)
+{
+ u32 mss = tcp_sk(sk)->advmss;
+ u32 icwnd = TCP_DEFAULT_INIT_RCVWND;
+ int rcvmem;
+
+ /* Limit to 10 segments if mss <= 1460,
+ * or 14600/mss segments, with a minimum of two segments.
+ */
+ if (mss > 1460)
+ icwnd = max_t(u32, (1460 * TCP_DEFAULT_INIT_RCVWND) / mss, 2);
+
+ rcvmem = SKB_TRUESIZE(mss + MAX_TCP_HEADER);
+ while (tcp_win_from_space(rcvmem) < mss)
+ rcvmem += 128;
+
+ rcvmem *= icwnd;
+
+ if (sk->sk_rcvbuf < rcvmem)
+ sk->sk_rcvbuf = min(rcvmem, sysctl_tcp_rmem[2]);
+}
+
+/* 4. Try to fixup all. It is made immediately after connection enters
+ * established state.
+ */
+static void tcp_init_buffer_space(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ int maxwin;
+
+ if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK))
+ tcp_fixup_rcvbuf(sk);
+ if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
+ tcp_fixup_sndbuf(sk);
+
+ tp->rcvq_space.space = tp->rcv_wnd;
+
+ maxwin = tcp_full_space(sk);
+
+ if (tp->window_clamp >= maxwin) {
+ tp->window_clamp = maxwin;
+
+ if (sysctl_tcp_app_win && maxwin > 4 * tp->advmss)
+ tp->window_clamp = max(maxwin -
+ (maxwin >> sysctl_tcp_app_win),
+ 4 * tp->advmss);
+ }
+
+ /* Force reservation of one segment. */
+ if (sysctl_tcp_app_win &&
+ tp->window_clamp > 2 * tp->advmss &&
+ tp->window_clamp + tp->advmss > maxwin)
+ tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss);
+
+ tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
+ tp->snd_cwnd_stamp = tcp_time_stamp;
+}
+
+/* 5. Recalculate window clamp after socket hit its memory bounds. */
+static void tcp_clamp_window(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct inet_connection_sock *icsk = inet_csk(sk);
+
+ icsk->icsk_ack.quick = 0;
+
+ if (sk->sk_rcvbuf < sysctl_tcp_rmem[2] &&
+ !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
+ !sk_under_memory_pressure(sk) &&
+ sk_memory_allocated(sk) < sk_prot_mem_limits(sk, 0)) {
+ sk->sk_rcvbuf = min(atomic_read(&sk->sk_rmem_alloc),
+ sysctl_tcp_rmem[2]);
+ }
+ if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf)
+ tp->rcv_ssthresh = min(tp->window_clamp, 2U * tp->advmss);
+}
+
+/* Initialize RCV_MSS value.
+ * RCV_MSS is an our guess about MSS used by the peer.
+ * We haven't any direct information about the MSS.
+ * It's better to underestimate the RCV_MSS rather than overestimate.
+ * Overestimations make us ACKing less frequently than needed.
+ * Underestimations are more easy to detect and fix by tcp_measure_rcv_mss().
+ */
+void tcp_initialize_rcv_mss(struct sock *sk)
+{
+ const struct tcp_sock *tp = tcp_sk(sk);
+ unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache);
+
+ hint = min(hint, tp->rcv_wnd / 2);
+ hint = min(hint, TCP_MSS_DEFAULT);
+ hint = max(hint, TCP_MIN_MSS);
+
+ inet_csk(sk)->icsk_ack.rcv_mss = hint;
+}
+EXPORT_SYMBOL(tcp_initialize_rcv_mss);
+
+/* Receiver "autotuning" code.
+ *
+ * The algorithm for RTT estimation w/o timestamps is based on
+ * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL.
+ * <http://public.lanl.gov/radiant/pubs.html#DRS>
+ *
+ * More detail on this code can be found at
+ * <http://staff.psc.edu/jheffner/>,
+ * though this reference is out of date. A new paper
+ * is pending.
+ */
+static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
+{
+ u32 new_sample = tp->rcv_rtt_est.rtt;
+ long m = sample;
+
+ if (m == 0)
+ m = 1;
+
+ if (new_sample != 0) {
+ /* If we sample in larger samples in the non-timestamp
+ * case, we could grossly overestimate the RTT especially
+ * with chatty applications or bulk transfer apps which
+ * are stalled on filesystem I/O.
+ *
+ * Also, since we are only going for a minimum in the
+ * non-timestamp case, we do not smooth things out
+ * else with timestamps disabled convergence takes too
+ * long.
+ */
+ if (!win_dep) {
+ m -= (new_sample >> 3);
+ new_sample += m;
+ } else {
+ m <<= 3;
+ if (m < new_sample)
+ new_sample = m;
+ }
+ } else {
+ /* No previous measure. */
+ new_sample = m << 3;
+ }
+
+ if (tp->rcv_rtt_est.rtt != new_sample)
+ tp->rcv_rtt_est.rtt = new_sample;
+}
+
+static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
+{
+ if (tp->rcv_rtt_est.time == 0)
+ goto new_measure;
+ if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
+ return;
+ tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rcv_rtt_est.time, 1);
+
+new_measure:
+ tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
+ tp->rcv_rtt_est.time = tcp_time_stamp;
+}
+
+static inline void tcp_rcv_rtt_measure_ts(struct sock *sk,
+ const struct sk_buff *skb)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ if (tp->rx_opt.rcv_tsecr &&
+ (TCP_SKB_CB(skb)->end_seq -
+ TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss))
+ tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rx_opt.rcv_tsecr, 0);
+}
+
+/*
+ * This function should be called every time data is copied to user space.
+ * It calculates the appropriate TCP receive buffer space.
+ */
+void tcp_rcv_space_adjust(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ int time;
+ int space;
+
+ if (tp->rcvq_space.time == 0)
+ goto new_measure;
+
+ time = tcp_time_stamp - tp->rcvq_space.time;
+ if (time < (tp->rcv_rtt_est.rtt >> 3) || tp->rcv_rtt_est.rtt == 0)
+ return;
+
+ space = 2 * (tp->copied_seq - tp->rcvq_space.seq);
+
+ space = max(tp->rcvq_space.space, space);
+
+ if (tp->rcvq_space.space != space) {
+ int rcvmem;
+
+ tp->rcvq_space.space = space;
+
+ if (sysctl_tcp_moderate_rcvbuf &&
+ !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
+ int new_clamp = space;
+
+ /* Receive space grows, normalize in order to
+ * take into account packet headers and sk_buff
+ * structure overhead.
+ */
+ space /= tp->advmss;
+ if (!space)
+ space = 1;
+ rcvmem = SKB_TRUESIZE(tp->advmss + MAX_TCP_HEADER);
+ while (tcp_win_from_space(rcvmem) < tp->advmss)
+ rcvmem += 128;
+ space *= rcvmem;
+ space = min(space, sysctl_tcp_rmem[2]);
+ if (space > sk->sk_rcvbuf) {
+ sk->sk_rcvbuf = space;
+
+ /* Make the window clamp follow along. */
+ tp->window_clamp = new_clamp;
+ }
+ }
+ }
+
+new_measure:
+ tp->rcvq_space.seq = tp->copied_seq;
+ tp->rcvq_space.time = tcp_time_stamp;
+}
+
+/* There is something which you must keep in mind when you analyze the
+ * behavior of the tp->ato delayed ack timeout interval. When a
+ * connection starts up, we want to ack as quickly as possible. The
+ * problem is that "good" TCP's do slow start at the beginning of data
+ * transmission. The means that until we send the first few ACK's the
+ * sender will sit on his end and only queue most of his data, because
+ * he can only send snd_cwnd unacked packets at any given time. For
+ * each ACK we send, he increments snd_cwnd and transmits more of his
+ * queue. -DaveM
+ */
+static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct inet_connection_sock *icsk = inet_csk(sk);
+ u32 now;
+
+ inet_csk_schedule_ack(sk);
+
+ tcp_measure_rcv_mss(sk, skb);
+
+ tcp_rcv_rtt_measure(tp);
+
+ now = tcp_time_stamp;
+
+ if (!icsk->icsk_ack.ato) {
+ /* The _first_ data packet received, initialize
+ * delayed ACK engine.
+ */
+ tcp_incr_quickack(sk);
+ icsk->icsk_ack.ato = TCP_ATO_MIN;
+ } else {
+ int m = now - icsk->icsk_ack.lrcvtime;
+
+ if (m <= TCP_ATO_MIN / 2) {
+ /* The fastest case is the first. */
+ icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2;
+ } else if (m < icsk->icsk_ack.ato) {
+ icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m;
+ if (icsk->icsk_ack.ato > icsk->icsk_rto)
+ icsk->icsk_ack.ato = icsk->icsk_rto;
+ } else if (m > icsk->icsk_rto) {
+ /* Too long gap. Apparently sender failed to
+ * restart window, so that we send ACKs quickly.
+ */
+ tcp_incr_quickack(sk);
+ sk_mem_reclaim(sk);
+ }
+ }
+ icsk->icsk_ack.lrcvtime = now;
+
+ TCP_ECN_check_ce(tp, skb);
+
+ if (skb->len >= 128)
+ tcp_grow_window(sk, skb);
+}
+
+/* Called to compute a smoothed rtt estimate. The data fed to this
+ * routine either comes from timestamps, or from segments that were
+ * known _not_ to have been retransmitted [see Karn/Partridge
+ * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
+ * piece by Van Jacobson.
+ * NOTE: the next three routines used to be one big routine.
+ * To save cycles in the RFC 1323 implementation it was better to break
+ * it up into three procedures. -- erics
+ */
+static void tcp_rtt_estimator(struct sock *sk, const __u32 mrtt)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ long m = mrtt; /* RTT */
+
+ /* The following amusing code comes from Jacobson's
+ * article in SIGCOMM '88. Note that rtt and mdev
+ * are scaled versions of rtt and mean deviation.
+ * This is designed to be as fast as possible
+ * m stands for "measurement".
+ *
+ * On a 1990 paper the rto value is changed to:
+ * RTO = rtt + 4 * mdev
+ *
+ * Funny. This algorithm seems to be very broken.
+ * These formulae increase RTO, when it should be decreased, increase
+ * too slowly, when it should be increased quickly, decrease too quickly
+ * etc. I guess in BSD RTO takes ONE value, so that it is absolutely
+ * does not matter how to _calculate_ it. Seems, it was trap
+ * that VJ failed to avoid. 8)
+ */
+ if (m == 0)
+ m = 1;
+ if (tp->srtt != 0) {
+ m -= (tp->srtt >> 3); /* m is now error in rtt est */
+ tp->srtt += m; /* rtt = 7/8 rtt + 1/8 new */
+ if (m < 0) {
+ m = -m; /* m is now abs(error) */
+ m -= (tp->mdev >> 2); /* similar update on mdev */
+ /* This is similar to one of Eifel findings.
+ * Eifel blocks mdev updates when rtt decreases.
+ * This solution is a bit different: we use finer gain
+ * for mdev in this case (alpha*beta).
+ * Like Eifel it also prevents growth of rto,
+ * but also it limits too fast rto decreases,
+ * happening in pure Eifel.
+ */
+ if (m > 0)
+ m >>= 3;
+ } else {
+ m -= (tp->mdev >> 2); /* similar update on mdev */
+ }
+ tp->mdev += m; /* mdev = 3/4 mdev + 1/4 new */
+ if (tp->mdev > tp->mdev_max) {
+ tp->mdev_max = tp->mdev;
+ if (tp->mdev_max > tp->rttvar)
+ tp->rttvar = tp->mdev_max;
+ }
+ if (after(tp->snd_una, tp->rtt_seq)) {
+ if (tp->mdev_max < tp->rttvar)
+ tp->rttvar -= (tp->rttvar - tp->mdev_max) >> 2;
+ tp->rtt_seq = tp->snd_nxt;
+ tp->mdev_max = tcp_rto_min(sk);
+ }
+ } else {
+ /* no previous measure. */
+ tp->srtt = m << 3; /* take the measured time to be rtt */
+ tp->mdev = m << 1; /* make sure rto = 3*rtt */
+ tp->mdev_max = tp->rttvar = max(tp->mdev, tcp_rto_min(sk));
+ tp->rtt_seq = tp->snd_nxt;
+ }
+}
+
+/* Calculate rto without backoff. This is the second half of Van Jacobson's
+ * routine referred to above.
+ */
+static inline void tcp_set_rto(struct sock *sk)
+{
+ const struct tcp_sock *tp = tcp_sk(sk);
+ /* Old crap is replaced with new one. 8)
+ *
+ * More seriously:
+ * 1. If rtt variance happened to be less 50msec, it is hallucination.
+ * It cannot be less due to utterly erratic ACK generation made
+ * at least by solaris and freebsd. "Erratic ACKs" has _nothing_
+ * to do with delayed acks, because at cwnd>2 true delack timeout
+ * is invisible. Actually, Linux-2.4 also generates erratic
+ * ACKs in some circumstances.
+ */
+ inet_csk(sk)->icsk_rto = __tcp_set_rto(tp);
+
+ /* 2. Fixups made earlier cannot be right.
+ * If we do not estimate RTO correctly without them,
+ * all the algo is pure shit and should be replaced
+ * with correct one. It is exactly, which we pretend to do.
+ */
+
+ /* NOTE: clamping at TCP_RTO_MIN is not required, current algo
+ * guarantees that rto is higher.
+ */
+ tcp_bound_rto(sk);
+}
+
+/* Save metrics learned by this TCP session.
+ This function is called only, when TCP finishes successfully
+ i.e. when it enters TIME-WAIT or goes from LAST-ACK to CLOSE.
+ */
+void tcp_update_metrics(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct dst_entry *dst = __sk_dst_get(sk);
+
+ if (sysctl_tcp_nometrics_save)
+ return;
+
+ dst_confirm(dst);
+
+ if (dst && (dst->flags & DST_HOST)) {
+ const struct inet_connection_sock *icsk = inet_csk(sk);
+ int m;
+ unsigned long rtt;
+
+ if (icsk->icsk_backoff || !tp->srtt) {
+ /* This session failed to estimate rtt. Why?
+ * Probably, no packets returned in time.
+ * Reset our results.
+ */
+ if (!(dst_metric_locked(dst, RTAX_RTT)))
+ dst_metric_set(dst, RTAX_RTT, 0);
+ return;
+ }
+
+ rtt = dst_metric_rtt(dst, RTAX_RTT);
+ m = rtt - tp->srtt;
+
+ /* If newly calculated rtt larger than stored one,
+ * store new one. Otherwise, use EWMA. Remember,
+ * rtt overestimation is always better than underestimation.
+ */
+ if (!(dst_metric_locked(dst, RTAX_RTT))) {
+ if (m <= 0)
+ set_dst_metric_rtt(dst, RTAX_RTT, tp->srtt);
+ else
+ set_dst_metric_rtt(dst, RTAX_RTT, rtt - (m >> 3));
+ }
+
+ if (!(dst_metric_locked(dst, RTAX_RTTVAR))) {
+ unsigned long var;
+ if (m < 0)
+ m = -m;
+
+ /* Scale deviation to rttvar fixed point */
+ m >>= 1;
+ if (m < tp->mdev)
+ m = tp->mdev;
+
+ var = dst_metric_rtt(dst, RTAX_RTTVAR);
+ if (m >= var)
+ var = m;
+ else
+ var -= (var - m) >> 2;
+
+ set_dst_metric_rtt(dst, RTAX_RTTVAR, var);
+ }
+
+ if (tcp_in_initial_slowstart(tp)) {
+ /* Slow start still did not finish. */
+ if (dst_metric(dst, RTAX_SSTHRESH) &&
+ !dst_metric_locked(dst, RTAX_SSTHRESH) &&
+ (tp->snd_cwnd >> 1) > dst_metric(dst, RTAX_SSTHRESH))
+ dst_metric_set(dst, RTAX_SSTHRESH, tp->snd_cwnd >> 1);
+ if (!dst_metric_locked(dst, RTAX_CWND) &&
+ tp->snd_cwnd > dst_metric(dst, RTAX_CWND))
+ dst_metric_set(dst, RTAX_CWND, tp->snd_cwnd);
+ } else if (tp->snd_cwnd > tp->snd_ssthresh &&
+ icsk->icsk_ca_state == TCP_CA_Open) {
+ /* Cong. avoidance phase, cwnd is reliable. */
+ if (!dst_metric_locked(dst, RTAX_SSTHRESH))
+ dst_metric_set(dst, RTAX_SSTHRESH,
+ max(tp->snd_cwnd >> 1, tp->snd_ssthresh));
+ if (!dst_metric_locked(dst, RTAX_CWND))
+ dst_metric_set(dst, RTAX_CWND,
+ (dst_metric(dst, RTAX_CWND) +
+ tp->snd_cwnd) >> 1);
+ } else {
+ /* Else slow start did not finish, cwnd is non-sense,
+ ssthresh may be also invalid.
+ */
+ if (!dst_metric_locked(dst, RTAX_CWND))
+ dst_metric_set(dst, RTAX_CWND,
+ (dst_metric(dst, RTAX_CWND) +
+ tp->snd_ssthresh) >> 1);
+ if (dst_metric(dst, RTAX_SSTHRESH) &&
+ !dst_metric_locked(dst, RTAX_SSTHRESH) &&
+ tp->snd_ssthresh > dst_metric(dst, RTAX_SSTHRESH))
+ dst_metric_set(dst, RTAX_SSTHRESH, tp->snd_ssthresh);
+ }
+
+ if (!dst_metric_locked(dst, RTAX_REORDERING)) {
+ if (dst_metric(dst, RTAX_REORDERING) < tp->reordering &&
+ tp->reordering != sysctl_tcp_reordering)
+ dst_metric_set(dst, RTAX_REORDERING, tp->reordering);
+ }
+ }
+}
+
+__u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst)
+{
+ __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
+
+ if (!cwnd)
+ cwnd = TCP_INIT_CWND;
+ return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
+}
+
+/* Set slow start threshold and cwnd not falling to slow start */
+void tcp_enter_cwr(struct sock *sk, const int set_ssthresh)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ const struct inet_connection_sock *icsk = inet_csk(sk);
+
+ tp->prior_ssthresh = 0;
+ tp->bytes_acked = 0;
+ if (icsk->icsk_ca_state < TCP_CA_CWR) {
+ tp->undo_marker = 0;
+ if (set_ssthresh)
+ tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
+ tp->snd_cwnd = min(tp->snd_cwnd,
+ tcp_packets_in_flight(tp) + 1U);
+ tp->snd_cwnd_cnt = 0;
+ tp->high_seq = tp->snd_nxt;
+ tp->snd_cwnd_stamp = tcp_time_stamp;
+ TCP_ECN_queue_cwr(tp);
+
+ tcp_set_ca_state(sk, TCP_CA_CWR);
+ }
+}
+
+/*
+ * Packet counting of FACK is based on in-order assumptions, therefore TCP
+ * disables it when reordering is detected
+ */
+static void tcp_disable_fack(struct tcp_sock *tp)
+{
+ /* RFC3517 uses different metric in lost marker => reset on change */
+ if (tcp_is_fack(tp))
+ tp->lost_skb_hint = NULL;
+ tp->rx_opt.sack_ok &= ~TCP_FACK_ENABLED;
+}
+
+/* Take a notice that peer is sending D-SACKs */
+static void tcp_dsack_seen(struct tcp_sock *tp)
+{
+ tp->rx_opt.sack_ok |= TCP_DSACK_SEEN;
+}
+
+/* Initialize metrics on socket. */
+
+static void tcp_init_metrics(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct dst_entry *dst = __sk_dst_get(sk);
+
+ if (dst == NULL)
+ goto reset;
+
+ dst_confirm(dst);
+
+ if (dst_metric_locked(dst, RTAX_CWND))
+ tp->snd_cwnd_clamp = dst_metric(dst, RTAX_CWND);
+ if (dst_metric(dst, RTAX_SSTHRESH)) {
+ tp->snd_ssthresh = dst_metric(dst, RTAX_SSTHRESH);
+ if (tp->snd_ssthresh > tp->snd_cwnd_clamp)
+ tp->snd_ssthresh = tp->snd_cwnd_clamp;
+ } else {
+ /* ssthresh may have been reduced unnecessarily during.
+ * 3WHS. Restore it back to its initial default.
+ */
+ tp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
+ }
+ if (dst_metric(dst, RTAX_REORDERING) &&
+ tp->reordering != dst_metric(dst, RTAX_REORDERING)) {
+ tcp_disable_fack(tp);
+ tp->reordering = dst_metric(dst, RTAX_REORDERING);
+ }
+
+ if (dst_metric(dst, RTAX_RTT) == 0 || tp->srtt == 0)
+ goto reset;
+
+ /* Initial rtt is determined from SYN,SYN-ACK.
+ * The segment is small and rtt may appear much
+ * less than real one. Use per-dst memory
+ * to make it more realistic.
+ *
+ * A bit of theory. RTT is time passed after "normal" sized packet
+ * is sent until it is ACKed. In normal circumstances sending small
+ * packets force peer to delay ACKs and calculation is correct too.
+ * The algorithm is adaptive and, provided we follow specs, it
+ * NEVER underestimate RTT. BUT! If peer tries to make some clever
+ * tricks sort of "quick acks" for time long enough to decrease RTT
+ * to low value, and then abruptly stops to do it and starts to delay
+ * ACKs, wait for troubles.
+ */
+ if (dst_metric_rtt(dst, RTAX_RTT) > tp->srtt) {
+ tp->srtt = dst_metric_rtt(dst, RTAX_RTT);
+ tp->rtt_seq = tp->snd_nxt;
+ }
+ if (dst_metric_rtt(dst, RTAX_RTTVAR) > tp->mdev) {
+ tp->mdev = dst_metric_rtt(dst, RTAX_RTTVAR);
+ tp->mdev_max = tp->rttvar = max(tp->mdev, tcp_rto_min(sk));
+ }
+ tcp_set_rto(sk);
+reset:
+ if (tp->srtt == 0) {
+ /* RFC2988bis: We've failed to get a valid RTT sample from
+ * 3WHS. This is most likely due to retransmission,
+ * including spurious one. Reset the RTO back to 3secs
+ * from the more aggressive 1sec to avoid more spurious
+ * retransmission.
+ */
+ tp->mdev = tp->mdev_max = tp->rttvar = TCP_TIMEOUT_FALLBACK;
+ inet_csk(sk)->icsk_rto = TCP_TIMEOUT_FALLBACK;
+ }
+ /* Cut cwnd down to 1 per RFC5681 if SYN or SYN-ACK has been
+ * retransmitted. In light of RFC2988bis' more aggressive 1sec
+ * initRTO, we only reset cwnd when more than 1 SYN/SYN-ACK
+ * retransmission has occurred.
+ */
+ if (tp->total_retrans > 1)
+ tp->snd_cwnd = 1;
+ else
+ tp->snd_cwnd = tcp_init_cwnd(tp, dst);
+ tp->snd_cwnd_stamp = tcp_time_stamp;
+}
+
+static void tcp_update_reordering(struct sock *sk, const int metric,
+ const int ts)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ if (metric > tp->reordering) {
+ int mib_idx;
+
+ tp->reordering = min(TCP_MAX_REORDERING, metric);
+
+ /* This exciting event is worth to be remembered. 8) */
+ if (ts)
+ mib_idx = LINUX_MIB_TCPTSREORDER;
+ else if (tcp_is_reno(tp))
+ mib_idx = LINUX_MIB_TCPRENOREORDER;
+ else if (tcp_is_fack(tp))
+ mib_idx = LINUX_MIB_TCPFACKREORDER;
+ else
+ mib_idx = LINUX_MIB_TCPSACKREORDER;
+
+ NET_INC_STATS_BH(sock_net(sk), mib_idx);
+#if FASTRETRANS_DEBUG > 1
+ printk(KERN_DEBUG "Disorder%d %d %u f%u s%u rr%d\n",
+ tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
+ tp->reordering,
+ tp->fackets_out,
+ tp->sacked_out,
+ tp->undo_marker ? tp->undo_retrans : 0);
+#endif
+ tcp_disable_fack(tp);
+ }
+}
+
+/* This must be called before lost_out is incremented */
+static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb)
+{
+ if ((tp->retransmit_skb_hint == NULL) ||
+ before(TCP_SKB_CB(skb)->seq,
+ TCP_SKB_CB(tp->retransmit_skb_hint)->seq))
+ tp->retransmit_skb_hint = skb;
+
+ if (!tp->lost_out ||
+ after(TCP_SKB_CB(skb)->end_seq, tp->retransmit_high))
+ tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
+}
+
+static void tcp_skb_mark_lost(struct tcp_sock *tp, struct sk_buff *skb)
+{
+ if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
+ tcp_verify_retransmit_hint(tp, skb);
+
+ tp->lost_out += tcp_skb_pcount(skb);
+ TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
+ }
+}
+
+static void tcp_skb_mark_lost_uncond_verify(struct tcp_sock *tp,
+ struct sk_buff *skb)
+{
+ tcp_verify_retransmit_hint(tp, skb);
+
+ if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
+ tp->lost_out += tcp_skb_pcount(skb);
+ TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
+ }
+}
+
+/* This procedure tags the retransmission queue when SACKs arrive.
+ *
+ * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
+ * Packets in queue with these bits set are counted in variables
+ * sacked_out, retrans_out and lost_out, correspondingly.
+ *
+ * Valid combinations are:
+ * Tag InFlight Description
+ * 0 1 - orig segment is in flight.
+ * S 0 - nothing flies, orig reached receiver.
+ * L 0 - nothing flies, orig lost by net.
+ * R 2 - both orig and retransmit are in flight.
+ * L|R 1 - orig is lost, retransmit is in flight.
+ * S|R 1 - orig reached receiver, retrans is still in flight.
+ * (L|S|R is logically valid, it could occur when L|R is sacked,
+ * but it is equivalent to plain S and code short-curcuits it to S.
+ * L|S is logically invalid, it would mean -1 packet in flight 8))
+ *
+ * These 6 states form finite state machine, controlled by the following events:
+ * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
+ * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
+ * 3. Loss detection event of two flavors:
+ * A. Scoreboard estimator decided the packet is lost.
+ * A'. Reno "three dupacks" marks head of queue lost.
+ * A''. Its FACK modification, head until snd.fack is lost.
+ * B. SACK arrives sacking SND.NXT at the moment, when the
+ * segment was retransmitted.
+ * 4. D-SACK added new rule: D-SACK changes any tag to S.
+ *
+ * It is pleasant to note, that state diagram turns out to be commutative,
+ * so that we are allowed not to be bothered by order of our actions,
+ * when multiple events arrive simultaneously. (see the function below).
+ *
+ * Reordering detection.
+ * --------------------
+ * Reordering metric is maximal distance, which a packet can be displaced
+ * in packet stream. With SACKs we can estimate it:
+ *
+ * 1. SACK fills old hole and the corresponding segment was not
+ * ever retransmitted -> reordering. Alas, we cannot use it
+ * when segment was retransmitted.
+ * 2. The last flaw is solved with D-SACK. D-SACK arrives
+ * for retransmitted and already SACKed segment -> reordering..
+ * Both of these heuristics are not used in Loss state, when we cannot
+ * account for retransmits accurately.
+ *
+ * SACK block validation.
+ * ----------------------
+ *
+ * SACK block range validation checks that the received SACK block fits to
+ * the expected sequence limits, i.e., it is between SND.UNA and SND.NXT.
+ * Note that SND.UNA is not included to the range though being valid because
+ * it means that the receiver is rather inconsistent with itself reporting
+ * SACK reneging when it should advance SND.UNA. Such SACK block this is
+ * perfectly valid, however, in light of RFC2018 which explicitly states
+ * that "SACK block MUST reflect the newest segment. Even if the newest
+ * segment is going to be discarded ...", not that it looks very clever
+ * in case of head skb. Due to potentional receiver driven attacks, we
+ * choose to avoid immediate execution of a walk in write queue due to
+ * reneging and defer head skb's loss recovery to standard loss recovery
+ * procedure that will eventually trigger (nothing forbids us doing this).
+ *
+ * Implements also blockage to start_seq wrap-around. Problem lies in the
+ * fact that though start_seq (s) is before end_seq (i.e., not reversed),
+ * there's no guarantee that it will be before snd_nxt (n). The problem
+ * happens when start_seq resides between end_seq wrap (e_w) and snd_nxt
+ * wrap (s_w):
+ *
+ * <- outs wnd -> <- wrapzone ->
+ * u e n u_w e_w s n_w
+ * | | | | | | |
+ * |<------------+------+----- TCP seqno space --------------+---------->|
+ * ...-- <2^31 ->| |<--------...
+ * ...---- >2^31 ------>| |<--------...
+ *
+ * Current code wouldn't be vulnerable but it's better still to discard such
+ * crazy SACK blocks. Doing this check for start_seq alone closes somewhat
+ * similar case (end_seq after snd_nxt wrap) as earlier reversed check in
+ * snd_nxt wrap -> snd_una region will then become "well defined", i.e.,
+ * equal to the ideal case (infinite seqno space without wrap caused issues).
+ *
+ * With D-SACK the lower bound is extended to cover sequence space below
+ * SND.UNA down to undo_marker, which is the last point of interest. Yet
+ * again, D-SACK block must not to go across snd_una (for the same reason as
+ * for the normal SACK blocks, explained above). But there all simplicity
+ * ends, TCP might receive valid D-SACKs below that. As long as they reside
+ * fully below undo_marker they do not affect behavior in anyway and can
+ * therefore be safely ignored. In rare cases (which are more or less
+ * theoretical ones), the D-SACK will nicely cross that boundary due to skb
+ * fragmentation and packet reordering past skb's retransmission. To consider
+ * them correctly, the acceptable range must be extended even more though
+ * the exact amount is rather hard to quantify. However, tp->max_window can
+ * be used as an exaggerated estimate.
+ */
+static int tcp_is_sackblock_valid(struct tcp_sock *tp, int is_dsack,
+ u32 start_seq, u32 end_seq)
+{
+ /* Too far in future, or reversed (interpretation is ambiguous) */
+ if (after(end_seq, tp->snd_nxt) || !before(start_seq, end_seq))
+ return 0;
+
+ /* Nasty start_seq wrap-around check (see comments above) */
+ if (!before(start_seq, tp->snd_nxt))
+ return 0;
+
+ /* In outstanding window? ...This is valid exit for D-SACKs too.
+ * start_seq == snd_una is non-sensical (see comments above)
+ */
+ if (after(start_seq, tp->snd_una))
+ return 1;
+
+ if (!is_dsack || !tp->undo_marker)
+ return 0;
+
+ /* ...Then it's D-SACK, and must reside below snd_una completely */
+ if (after(end_seq, tp->snd_una))
+ return 0;
+
+ if (!before(start_seq, tp->undo_marker))
+ return 1;
+
+ /* Too old */
+ if (!after(end_seq, tp->undo_marker))
+ return 0;
+
+ /* Undo_marker boundary crossing (overestimates a lot). Known already:
+ * start_seq < undo_marker and end_seq >= undo_marker.
+ */
+ return !before(start_seq, end_seq - tp->max_window);
+}
+
+/* Check for lost retransmit. This superb idea is borrowed from "ratehalving".
+ * Event "B". Later note: FACK people cheated me again 8), we have to account
+ * for reordering! Ugly, but should help.
+ *
+ * Search retransmitted skbs from write_queue that were sent when snd_nxt was
+ * less than what is now known to be received by the other end (derived from
+ * highest SACK block). Also calculate the lowest snd_nxt among the remaining
+ * retransmitted skbs to avoid some costly processing per ACKs.
+ */
+static void tcp_mark_lost_retrans(struct sock *sk)
+{
+ const struct inet_connection_sock *icsk = inet_csk(sk);
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct sk_buff *skb;
+ int cnt = 0;
+ u32 new_low_seq = tp->snd_nxt;
+ u32 received_upto = tcp_highest_sack_seq(tp);
+
+ if (!tcp_is_fack(tp) || !tp->retrans_out ||
+ !after(received_upto, tp->lost_retrans_low) ||
+ icsk->icsk_ca_state != TCP_CA_Recovery)
+ return;
+
+ tcp_for_write_queue(skb, sk) {
+ u32 ack_seq = TCP_SKB_CB(skb)->ack_seq;
+
+ if (skb == tcp_send_head(sk))
+ break;
+ if (cnt == tp->retrans_out)
+ break;
+ if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
+ continue;
+
+ if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS))
+ continue;
+
+ /* TODO: We would like to get rid of tcp_is_fack(tp) only
+ * constraint here (see above) but figuring out that at
+ * least tp->reordering SACK blocks reside between ack_seq
+ * and received_upto is not easy task to do cheaply with
+ * the available datastructures.
+ *
+ * Whether FACK should check here for tp->reordering segs
+ * in-between one could argue for either way (it would be
+ * rather simple to implement as we could count fack_count
+ * during the walk and do tp->fackets_out - fack_count).
+ */
+ if (after(received_upto, ack_seq)) {
+ TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
+ tp->retrans_out -= tcp_skb_pcount(skb);
+
+ tcp_skb_mark_lost_uncond_verify(tp, skb);
+ NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSTRETRANSMIT);
+ } else {
+ if (before(ack_seq, new_low_seq))
+ new_low_seq = ack_seq;
+ cnt += tcp_skb_pcount(skb);
+ }
+ }
+
+ if (tp->retrans_out)
+ tp->lost_retrans_low = new_low_seq;
+}
+
+static int tcp_check_dsack(struct sock *sk, const struct sk_buff *ack_skb,
+ struct tcp_sack_block_wire *sp, int num_sacks,
+ u32 prior_snd_una)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ u32 start_seq_0 = get_unaligned_be32(&sp[0].start_seq);
+ u32 end_seq_0 = get_unaligned_be32(&sp[0].end_seq);
+ int dup_sack = 0;
+
+ if (before(start_seq_0, TCP_SKB_CB(ack_skb)->ack_seq)) {
+ dup_sack = 1;
+ tcp_dsack_seen(tp);
+ NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDSACKRECV);
+ } else if (num_sacks > 1) {
+ u32 end_seq_1 = get_unaligned_be32(&sp[1].end_seq);
+ u32 start_seq_1 = get_unaligned_be32(&sp[1].start_seq);
+
+ if (!after(end_seq_0, end_seq_1) &&
+ !before(start_seq_0, start_seq_1)) {
+ dup_sack = 1;
+ tcp_dsack_seen(tp);
+ NET_INC_STATS_BH(sock_net(sk),
+ LINUX_MIB_TCPDSACKOFORECV);
+ }
+ }
+
+ /* D-SACK for already forgotten data... Do dumb counting. */
+ if (dup_sack && tp->undo_marker && tp->undo_retrans > 0 &&
+ !after(end_seq_0, prior_snd_una) &&
+ after(end_seq_0, tp->undo_marker))
+ tp->undo_retrans--;
+
+ return dup_sack;
+}
+
+struct tcp_sacktag_state {
+ int reord;
+ int fack_count;
+ int flag;
+};
+
+/* Check if skb is fully within the SACK block. In presence of GSO skbs,
+ * the incoming SACK may not exactly match but we can find smaller MSS
+ * aligned portion of it that matches. Therefore we might need to fragment
+ * which may fail and creates some hassle (caller must handle error case
+ * returns).
+ *
+ * FIXME: this could be merged to shift decision code
+ */
+static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb,
+ u32 start_seq, u32 end_seq)
+{
+ int in_sack, err;
+ unsigned int pkt_len;
+ unsigned int mss;
+
+ in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
+ !before(end_seq, TCP_SKB_CB(skb)->end_seq);
+
+ if (tcp_skb_pcount(skb) > 1 && !in_sack &&
+ after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
+ mss = tcp_skb_mss(skb);
+ in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
+
+ if (!in_sack) {
+ pkt_len = start_seq - TCP_SKB_CB(skb)->seq;
+ if (pkt_len < mss)
+ pkt_len = mss;
+ } else {
+ pkt_len = end_seq - TCP_SKB_CB(skb)->seq;
+ if (pkt_len < mss)
+ return -EINVAL;
+ }
+
+ /* Round if necessary so that SACKs cover only full MSSes
+ * and/or the remaining small portion (if present)
+ */
+ if (pkt_len > mss) {
+ unsigned int new_len = (pkt_len / mss) * mss;
+ if (!in_sack && new_len < pkt_len) {
+ new_len += mss;
+ if (new_len >= skb->len)
+ return 0;
+ }
+ pkt_len = new_len;
+ }
+ err = tcp_fragment(sk, skb, pkt_len, mss);
+ if (err < 0)
+ return err;
+ }
+
+ return in_sack;
+}
+
+/* Mark the given newly-SACKed range as such, adjusting counters and hints. */
+static u8 tcp_sacktag_one(struct sock *sk,
+ struct tcp_sacktag_state *state, u8 sacked,
+ u32 start_seq, u32 end_seq,
+ int dup_sack, int pcount)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ int fack_count = state->fack_count;
+
+ /* Account D-SACK for retransmitted packet. */
+ if (dup_sack && (sacked & TCPCB_RETRANS)) {
+ if (tp->undo_marker && tp->undo_retrans > 0 &&
+ after(end_seq, tp->undo_marker))
+ tp->undo_retrans--;
+ if (sacked & TCPCB_SACKED_ACKED)
+ state->reord = min(fack_count, state->reord);
+ }
+
+ /* Nothing to do; acked frame is about to be dropped (was ACKed). */
+ if (!after(end_seq, tp->snd_una))
+ return sacked;
+
+ if (!(sacked & TCPCB_SACKED_ACKED)) {
+ if (sacked & TCPCB_SACKED_RETRANS) {
+ /* If the segment is not tagged as lost,
+ * we do not clear RETRANS, believing
+ * that retransmission is still in flight.
+ */
+ if (sacked & TCPCB_LOST) {
+ sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
+ tp->lost_out -= pcount;
+ tp->retrans_out -= pcount;
+ }
+ } else {
+ if (!(sacked & TCPCB_RETRANS)) {
+ /* New sack for not retransmitted frame,
+ * which was in hole. It is reordering.
+ */
+ if (before(start_seq,
+ tcp_highest_sack_seq(tp)))
+ state->reord = min(fack_count,
+ state->reord);
+
+ /* SACK enhanced F-RTO (RFC4138; Appendix B) */
+ if (!after(end_seq, tp->frto_highmark))
+ state->flag |= FLAG_ONLY_ORIG_SACKED;
+ }
+
+ if (sacked & TCPCB_LOST) {
+ sacked &= ~TCPCB_LOST;
+ tp->lost_out -= pcount;
+ }
+ }
+
+ sacked |= TCPCB_SACKED_ACKED;
+ state->flag |= FLAG_DATA_SACKED;
+ tp->sacked_out += pcount;
+
+ fack_count += pcount;
+
+ /* Lost marker hint past SACKed? Tweak RFC3517 cnt */
+ if (!tcp_is_fack(tp) && (tp->lost_skb_hint != NULL) &&
+ before(start_seq, TCP_SKB_CB(tp->lost_skb_hint)->seq))
+ tp->lost_cnt_hint += pcount;
+
+ if (fack_count > tp->fackets_out)
+ tp->fackets_out = fack_count;
+ }
+
+ /* D-SACK. We can detect redundant retransmission in S|R and plain R
+ * frames and clear it. undo_retrans is decreased above, L|R frames
+ * are accounted above as well.
+ */
+ if (dup_sack && (sacked & TCPCB_SACKED_RETRANS)) {
+ sacked &= ~TCPCB_SACKED_RETRANS;
+ tp->retrans_out -= pcount;
+ }
+
+ return sacked;
+}
+
+/* Shift newly-SACKed bytes from this skb to the immediately previous
+ * already-SACKed sk_buff. Mark the newly-SACKed bytes as such.
+ */
+static int tcp_shifted_skb(struct sock *sk, struct sk_buff *skb,
+ struct tcp_sacktag_state *state,
+ unsigned int pcount, int shifted, int mss,
+ int dup_sack)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct sk_buff *prev = tcp_write_queue_prev(sk, skb);
+ u32 start_seq = TCP_SKB_CB(skb)->seq; /* start of newly-SACKed */
+ u32 end_seq = start_seq + shifted; /* end of newly-SACKed */
+
+ BUG_ON(!pcount);
+
+ /* Adjust counters and hints for the newly sacked sequence
+ * range but discard the return value since prev is already
+ * marked. We must tag the range first because the seq
+ * advancement below implicitly advances
+ * tcp_highest_sack_seq() when skb is highest_sack.
+ */
+ tcp_sacktag_one(sk, state, TCP_SKB_CB(skb)->sacked,
+ start_seq, end_seq, dup_sack, pcount);
+
+ if (skb == tp->lost_skb_hint)
+ tp->lost_cnt_hint += pcount;
+
+ TCP_SKB_CB(prev)->end_seq += shifted;
+ TCP_SKB_CB(skb)->seq += shifted;
+
+ skb_shinfo(prev)->gso_segs += pcount;
+ BUG_ON(skb_shinfo(skb)->gso_segs < pcount);
+ skb_shinfo(skb)->gso_segs -= pcount;
+
+ /* When we're adding to gso_segs == 1, gso_size will be zero,
+ * in theory this shouldn't be necessary but as long as DSACK
+ * code can come after this skb later on it's better to keep
+ * setting gso_size to something.
+ */
+ if (!skb_shinfo(prev)->gso_size) {
+ skb_shinfo(prev)->gso_size = mss;
+ skb_shinfo(prev)->gso_type = sk->sk_gso_type;
+ }
+
+ /* CHECKME: To clear or not to clear? Mimics normal skb currently */
+ if (skb_shinfo(skb)->gso_segs <= 1) {
+ skb_shinfo(skb)->gso_size = 0;
+ skb_shinfo(skb)->gso_type = 0;
+ }
+
+ /* Difference in this won't matter, both ACKed by the same cumul. ACK */
+ TCP_SKB_CB(prev)->sacked |= (TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS);
+
+ if (skb->len > 0) {
+ BUG_ON(!tcp_skb_pcount(skb));
+ NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKSHIFTED);
+ return 0;
+ }
+
+ /* Whole SKB was eaten :-) */
+
+ if (skb == tp->retransmit_skb_hint)
+ tp->retransmit_skb_hint = prev;
+ if (skb == tp->scoreboard_skb_hint)
+ tp->scoreboard_skb_hint = prev;
+ if (skb == tp->lost_skb_hint) {
+ tp->lost_skb_hint = prev;
+ tp->lost_cnt_hint -= tcp_skb_pcount(prev);
+ }
+
+ TCP_SKB_CB(prev)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
+ if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
+ TCP_SKB_CB(prev)->end_seq++;
+
+ if (skb == tcp_highest_sack(sk))
+ tcp_advance_highest_sack(sk, skb);
+
+ tcp_unlink_write_queue(skb, sk);
+ sk_wmem_free_skb(sk, skb);
+
+ NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKMERGED);
+
+ return 1;
+}
+
+/* I wish gso_size would have a bit more sane initialization than
+ * something-or-zero which complicates things
+ */
+static int tcp_skb_seglen(const struct sk_buff *skb)
+{
+ return tcp_skb_pcount(skb) == 1 ? skb->len : tcp_skb_mss(skb);
+}
+
+/* Shifting pages past head area doesn't work */
+static int skb_can_shift(const struct sk_buff *skb)
+{
+ return !skb_headlen(skb) && skb_is_nonlinear(skb);
+}
+//hub:CVE-2019-11477
+int tcp_skb_shift(struct sk_buff * to, struct sk_buff * from, int pcount, int shiftlen)
+{
+ /* TCP min gso_size is 8 bytes(TCP_MIN_GSO_SIZE)
+ * Since TCP_SKB_CB(skb)->tcp_gso_segs is 16 bits, we need
+ * to make sure not storing more then 65535*8 bytes per skb,
+ * event if current MSS is bigger.
+ */
+ if(unlikely(to->len + shiftlen >= 65535*TCP_MIN_GSO_SIZE))
+ return 0;
+ if(unlikely(tcp_skb_pcount(to) + pcount > 65535))
+ return 0;
+
+ return skb_shift(to, from, shiftlen);
+}
+
+/* Try collapsing SACK blocks spanning across multiple skbs to a single
+ * skb.
+ */
+static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb,
+ struct tcp_sacktag_state *state,
+ u32 start_seq, u32 end_seq,
+ int dup_sack)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct sk_buff *prev;
+ int mss;
+ int pcount = 0;
+ int len;
+ int in_sack;
+
+ if (!sk_can_gso(sk))
+ goto fallback;
+
+ /* Normally R but no L won't result in plain S */
+ if (!dup_sack &&
+ (TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_RETRANS)) == TCPCB_SACKED_RETRANS)
+ goto fallback;
+ if (!skb_can_shift(skb))
+ goto fallback;
+ /* This frame is about to be dropped (was ACKed). */
+ if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
+ goto fallback;
+
+ /* Can only happen with delayed DSACK + discard craziness */
+ if (unlikely(skb == tcp_write_queue_head(sk)))
+ goto fallback;
+ prev = tcp_write_queue_prev(sk, skb);
+
+ if ((TCP_SKB_CB(prev)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED)
+ goto fallback;
+
+ in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
+ !before(end_seq, TCP_SKB_CB(skb)->end_seq);
+
+ if (in_sack) {
+ len = skb->len;
+ pcount = tcp_skb_pcount(skb);
+ mss = tcp_skb_seglen(skb);
+
+ /* TODO: Fix DSACKs to not fragment already SACKed and we can
+ * drop this restriction as unnecessary
+ */
+ if (mss != tcp_skb_seglen(prev))
+ goto fallback;
+ } else {
+ if (!after(TCP_SKB_CB(skb)->end_seq, start_seq))
+ goto noop;
+ /* CHECKME: This is non-MSS split case only?, this will
+ * cause skipped skbs due to advancing loop btw, original
+ * has that feature too
+ */
+ if (tcp_skb_pcount(skb) <= 1)
+ goto noop;
+
+ in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
+ if (!in_sack) {
+ /* TODO: head merge to next could be attempted here
+ * if (!after(TCP_SKB_CB(skb)->end_seq, end_seq)),
+ * though it might not be worth of the additional hassle
+ *
+ * ...we can probably just fallback to what was done
+ * previously. We could try merging non-SACKed ones
+ * as well but it probably isn't going to buy off
+ * because later SACKs might again split them, and
+ * it would make skb timestamp tracking considerably
+ * harder problem.
+ */
+ goto fallback;
+ }
+
+ len = end_seq - TCP_SKB_CB(skb)->seq;
+ BUG_ON(len < 0);
+ BUG_ON(len > skb->len);
+
+ /* MSS boundaries should be honoured or else pcount will
+ * severely break even though it makes things bit trickier.
+ * Optimize common case to avoid most of the divides
+ */
+ mss = tcp_skb_mss(skb);
+
+ /* TODO: Fix DSACKs to not fragment already SACKed and we can
+ * drop this restriction as unnecessary
+ */
+ if (mss != tcp_skb_seglen(prev))
+ goto fallback;
+
+ if (len == mss) {
+ pcount = 1;
+ } else if (len < mss) {
+ goto noop;
+ } else {
+ pcount = len / mss;
+ len = pcount * mss;
+ }
+ }
+
+ /* tcp_sacktag_one() won't SACK-tag ranges below snd_una */
+ if (!after(TCP_SKB_CB(skb)->seq + len, tp->snd_una))
+ goto fallback;
+
+ if (!tcp_skb_shift(prev, skb, pcount, len)) //hub:CVE-2019-11477
+ goto fallback;
+ if (!tcp_shifted_skb(sk, skb, state, pcount, len, mss, dup_sack))
+ goto out;
+
+ /* Hole filled allows collapsing with the next as well, this is very
+ * useful when hole on every nth skb pattern happens
+ */
+ if (prev == tcp_write_queue_tail(sk))
+ goto out;
+ skb = tcp_write_queue_next(sk, prev);
+
+ if (!skb_can_shift(skb) ||
+ (skb == tcp_send_head(sk)) ||
+ ((TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED) ||
+ (mss != tcp_skb_seglen(skb)))
+ goto out;
+
+ len = skb->len;
+ //hub:CVE-2019-11477
+ pcount = tcp_skb_pcount(skb);
+ if (tcp_skb_shift(prev, skb, pcount, len)) {
+ tcp_shifted_skb(sk, skb, state, pcount, len, mss, 0);
+ }
+
+out:
+ state->fack_count += pcount;
+ return prev;
+
+noop:
+ return skb;
+
+fallback:
+ NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKSHIFTFALLBACK);
+ return NULL;
+}
+
+static struct sk_buff *tcp_sacktag_walk(struct sk_buff *skb, struct sock *sk,
+ struct tcp_sack_block *next_dup,
+ struct tcp_sacktag_state *state,
+ u32 start_seq, u32 end_seq,
+ int dup_sack_in)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct sk_buff *tmp;
+
+ tcp_for_write_queue_from(skb, sk) {
+ int in_sack = 0;
+ int dup_sack = dup_sack_in;
+
+ if (skb == tcp_send_head(sk))
+ break;
+
+ /* queue is in-order => we can short-circuit the walk early */
+ if (!before(TCP_SKB_CB(skb)->seq, end_seq))
+ break;
+
+ if ((next_dup != NULL) &&
+ before(TCP_SKB_CB(skb)->seq, next_dup->end_seq)) {
+ in_sack = tcp_match_skb_to_sack(sk, skb,
+ next_dup->start_seq,
+ next_dup->end_seq);
+ if (in_sack > 0)
+ dup_sack = 1;
+ }
+
+ /* skb reference here is a bit tricky to get right, since
+ * shifting can eat and free both this skb and the next,
+ * so not even _safe variant of the loop is enough.
+ */
+ if (in_sack <= 0) {
+ tmp = tcp_shift_skb_data(sk, skb, state,
+ start_seq, end_seq, dup_sack);
+ if (tmp != NULL) {
+ if (tmp != skb) {
+ skb = tmp;
+ continue;
+ }
+
+ in_sack = 0;
+ } else {
+ in_sack = tcp_match_skb_to_sack(sk, skb,
+ start_seq,
+ end_seq);
+ }
+ }
+
+ if (unlikely(in_sack < 0))
+ break;
+
+ if (in_sack) {
+ TCP_SKB_CB(skb)->sacked =
+ tcp_sacktag_one(sk,
+ state,
+ TCP_SKB_CB(skb)->sacked,
+ TCP_SKB_CB(skb)->seq,
+ TCP_SKB_CB(skb)->end_seq,
+ dup_sack,
+ tcp_skb_pcount(skb));
+
+ if (!before(TCP_SKB_CB(skb)->seq,
+ tcp_highest_sack_seq(tp)))
+ tcp_advance_highest_sack(sk, skb);
+ }
+
+ state->fack_count += tcp_skb_pcount(skb);
+ }
+ return skb;
+}
+
+/* Avoid all extra work that is being done by sacktag while walking in
+ * a normal way
+ */
+static struct sk_buff *tcp_sacktag_skip(struct sk_buff *skb, struct sock *sk,
+ struct tcp_sacktag_state *state,
+ u32 skip_to_seq)
+{
+ tcp_for_write_queue_from(skb, sk) {
+ if (skb == tcp_send_head(sk))
+ break;
+
+ if (after(TCP_SKB_CB(skb)->end_seq, skip_to_seq))
+ break;
+
+ state->fack_count += tcp_skb_pcount(skb);
+ }
+ return skb;
+}
+
+static struct sk_buff *tcp_maybe_skipping_dsack(struct sk_buff *skb,
+ struct sock *sk,
+ struct tcp_sack_block *next_dup,
+ struct tcp_sacktag_state *state,
+ u32 skip_to_seq)
+{
+ if (next_dup == NULL)
+ return skb;
+
+ if (before(next_dup->start_seq, skip_to_seq)) {
+ skb = tcp_sacktag_skip(skb, sk, state, next_dup->start_seq);
+ skb = tcp_sacktag_walk(skb, sk, NULL, state,
+ next_dup->start_seq, next_dup->end_seq,
+ 1);
+ }
+
+ return skb;
+}
+
+static int tcp_sack_cache_ok(const struct tcp_sock *tp, const struct tcp_sack_block *cache)
+{
+ return cache < tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
+}
+
+static int
+tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb,
+ u32 prior_snd_una)
+{
+ const struct inet_connection_sock *icsk = inet_csk(sk);
+ struct tcp_sock *tp = tcp_sk(sk);
+ const unsigned char *ptr = (skb_transport_header(ack_skb) +
+ TCP_SKB_CB(ack_skb)->sacked);
+ struct tcp_sack_block_wire *sp_wire = (struct tcp_sack_block_wire *)(ptr+2);
+ struct tcp_sack_block sp[TCP_NUM_SACKS];
+ struct tcp_sack_block *cache;
+ struct tcp_sacktag_state state;
+ struct sk_buff *skb;
+ int num_sacks = min(TCP_NUM_SACKS, (ptr[1] - TCPOLEN_SACK_BASE) >> 3);
+ int used_sacks;
+ int found_dup_sack = 0;
+ int i, j;
+ int first_sack_index;
+
+ state.flag = 0;
+ state.reord = tp->packets_out;
+
+ if (!tp->sacked_out) {
+ if (WARN_ON(tp->fackets_out))
+ tp->fackets_out = 0;
+ tcp_highest_sack_reset(sk);
+ }
+
+ found_dup_sack = tcp_check_dsack(sk, ack_skb, sp_wire,
+ num_sacks, prior_snd_una);
+ if (found_dup_sack)
+ state.flag |= FLAG_DSACKING_ACK;
+
+ /* Eliminate too old ACKs, but take into
+ * account more or less fresh ones, they can
+ * contain valid SACK info.
+ */
+ if (before(TCP_SKB_CB(ack_skb)->ack_seq, prior_snd_una - tp->max_window))
+ return 0;
+
+ if (!tp->packets_out)
+ goto out;
+
+ used_sacks = 0;
+ first_sack_index = 0;
+ for (i = 0; i < num_sacks; i++) {
+ int dup_sack = !i && found_dup_sack;
+
+ sp[used_sacks].start_seq = get_unaligned_be32(&sp_wire[i].start_seq);
+ sp[used_sacks].end_seq = get_unaligned_be32(&sp_wire[i].end_seq);
+
+ if (!tcp_is_sackblock_valid(tp, dup_sack,
+ sp[used_sacks].start_seq,
+ sp[used_sacks].end_seq)) {
+ int mib_idx;
+
+ if (dup_sack) {
+ if (!tp->undo_marker)
+ mib_idx = LINUX_MIB_TCPDSACKIGNOREDNOUNDO;
+ else
+ mib_idx = LINUX_MIB_TCPDSACKIGNOREDOLD;
+ } else {
+ /* Don't count olds caused by ACK reordering */
+ if ((TCP_SKB_CB(ack_skb)->ack_seq != tp->snd_una) &&
+ !after(sp[used_sacks].end_seq, tp->snd_una))
+ continue;
+ mib_idx = LINUX_MIB_TCPSACKDISCARD;
+ }
+
+ NET_INC_STATS_BH(sock_net(sk), mib_idx);
+ if (i == 0)
+ first_sack_index = -1;
+ continue;
+ }
+
+ /* Ignore very old stuff early */
+ if (!after(sp[used_sacks].end_seq, prior_snd_una))
+ continue;
+
+ used_sacks++;
+ }
+
+ /* order SACK blocks to allow in order walk of the retrans queue */
+ for (i = used_sacks - 1; i > 0; i--) {
+ for (j = 0; j < i; j++) {
+ if (after(sp[j].start_seq, sp[j + 1].start_seq)) {
+ swap(sp[j], sp[j + 1]);
+
+ /* Track where the first SACK block goes to */
+ if (j == first_sack_index)
+ first_sack_index = j + 1;
+ }
+ }
+ }
+
+ skb = tcp_write_queue_head(sk);
+ state.fack_count = 0;
+ i = 0;
+
+ if (!tp->sacked_out) {
+ /* It's already past, so skip checking against it */
+ cache = tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
+ } else {
+ cache = tp->recv_sack_cache;
+ /* Skip empty blocks in at head of the cache */
+ while (tcp_sack_cache_ok(tp, cache) && !cache->start_seq &&
+ !cache->end_seq)
+ cache++;
+ }
+
+ while (i < used_sacks) {
+ u32 start_seq = sp[i].start_seq;
+ u32 end_seq = sp[i].end_seq;
+ int dup_sack = (found_dup_sack && (i == first_sack_index));
+ struct tcp_sack_block *next_dup = NULL;
+
+ if (found_dup_sack && ((i + 1) == first_sack_index))
+ next_dup = &sp[i + 1];
+
+ /* Skip too early cached blocks */
+ while (tcp_sack_cache_ok(tp, cache) &&
+ !before(start_seq, cache->end_seq))
+ cache++;
+
+ /* Can skip some work by looking recv_sack_cache? */
+ if (tcp_sack_cache_ok(tp, cache) && !dup_sack &&
+ after(end_seq, cache->start_seq)) {
+
+ /* Head todo? */
+ if (before(start_seq, cache->start_seq)) {
+ skb = tcp_sacktag_skip(skb, sk, &state,
+ start_seq);
+ skb = tcp_sacktag_walk(skb, sk, next_dup,
+ &state,
+ start_seq,
+ cache->start_seq,
+ dup_sack);
+ }
+
+ /* Rest of the block already fully processed? */
+ if (!after(end_seq, cache->end_seq))
+ goto advance_sp;
+
+ skb = tcp_maybe_skipping_dsack(skb, sk, next_dup,
+ &state,
+ cache->end_seq);
+
+ /* ...tail remains todo... */
+ if (tcp_highest_sack_seq(tp) == cache->end_seq) {
+ /* ...but better entrypoint exists! */
+ skb = tcp_highest_sack(sk);
+ if (skb == NULL)
+ break;
+ state.fack_count = tp->fackets_out;
+ cache++;
+ goto walk;
+ }
+
+ skb = tcp_sacktag_skip(skb, sk, &state, cache->end_seq);
+ /* Check overlap against next cached too (past this one already) */
+ cache++;
+ continue;
+ }
+
+ if (!before(start_seq, tcp_highest_sack_seq(tp))) {
+ skb = tcp_highest_sack(sk);
+ if (skb == NULL)
+ break;
+ state.fack_count = tp->fackets_out;
+ }
+ skb = tcp_sacktag_skip(skb, sk, &state, start_seq);
+
+walk:
+ skb = tcp_sacktag_walk(skb, sk, next_dup, &state,
+ start_seq, end_seq, dup_sack);
+
+advance_sp:
+ /* SACK enhanced FRTO (RFC4138, Appendix B): Clearing correct
+ * due to in-order walk
+ */
+ if (after(end_seq, tp->frto_highmark))
+ state.flag &= ~FLAG_ONLY_ORIG_SACKED;
+
+ i++;
+ }
+
+ /* Clear the head of the cache sack blocks so we can skip it next time */
+ for (i = 0; i < ARRAY_SIZE(tp->recv_sack_cache) - used_sacks; i++) {
+ tp->recv_sack_cache[i].start_seq = 0;
+ tp->recv_sack_cache[i].end_seq = 0;
+ }
+ for (j = 0; j < used_sacks; j++)
+ tp->recv_sack_cache[i++] = sp[j];
+
+ tcp_mark_lost_retrans(sk);
+
+ tcp_verify_left_out(tp);
+
+ if ((state.reord < tp->fackets_out) &&
+ ((icsk->icsk_ca_state != TCP_CA_Loss) || tp->undo_marker) &&
+ (!tp->frto_highmark || after(tp->snd_una, tp->frto_highmark)))
+ tcp_update_reordering(sk, tp->fackets_out - state.reord, 0);
+
+out:
+
+#if FASTRETRANS_DEBUG > 0
+ WARN_ON((int)tp->sacked_out < 0);
+ WARN_ON((int)tp->lost_out < 0);
+ WARN_ON((int)tp->retrans_out < 0);
+ WARN_ON((int)tcp_packets_in_flight(tp) < 0);
+#endif
+ return state.flag;
+}
+
+/* Limits sacked_out so that sum with lost_out isn't ever larger than
+ * packets_out. Returns zero if sacked_out adjustement wasn't necessary.
+ */
+static int tcp_limit_reno_sacked(struct tcp_sock *tp)
+{
+ u32 holes;
+
+ holes = max(tp->lost_out, 1U);
+ holes = min(holes, tp->packets_out);
+
+ if ((tp->sacked_out + holes) > tp->packets_out) {
+ tp->sacked_out = tp->packets_out - holes;
+ return 1;
+ }
+ return 0;
+}
+
+/* If we receive more dupacks than we expected counting segments
+ * in assumption of absent reordering, interpret this as reordering.
+ * The only another reason could be bug in receiver TCP.
+ */
+static void tcp_check_reno_reordering(struct sock *sk, const int addend)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ if (tcp_limit_reno_sacked(tp))
+ tcp_update_reordering(sk, tp->packets_out + addend, 0);
+}
+
+/* Emulate SACKs for SACKless connection: account for a new dupack. */
+
+static void tcp_add_reno_sack(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ tp->sacked_out++;
+ tcp_check_reno_reordering(sk, 0);
+ tcp_verify_left_out(tp);
+}
+
+/* Account for ACK, ACKing some data in Reno Recovery phase. */
+
+static void tcp_remove_reno_sacks(struct sock *sk, int acked)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ if (acked > 0) {
+ /* One ACK acked hole. The rest eat duplicate ACKs. */
+ if (acked - 1 >= tp->sacked_out)
+ tp->sacked_out = 0;
+ else
+ tp->sacked_out -= acked - 1;
+ }
+ tcp_check_reno_reordering(sk, acked);
+ tcp_verify_left_out(tp);
+}
+
+static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
+{
+ tp->sacked_out = 0;
+}
+
+static int tcp_is_sackfrto(const struct tcp_sock *tp)
+{
+ return (sysctl_tcp_frto == 0x2) && !tcp_is_reno(tp);
+}
+
+/* F-RTO can only be used if TCP has never retransmitted anything other than
+ * head (SACK enhanced variant from Appendix B of RFC4138 is more robust here)
+ */
+int tcp_use_frto(struct sock *sk)
+{
+ const struct tcp_sock *tp = tcp_sk(sk);
+ const struct inet_connection_sock *icsk = inet_csk(sk);
+ struct sk_buff *skb;
+
+ if (!sysctl_tcp_frto)
+ return 0;
+
+ /* MTU probe and F-RTO won't really play nicely along currently */
+ if (icsk->icsk_mtup.probe_size)
+ return 0;
+
+ if (tcp_is_sackfrto(tp))
+ return 1;
+
+ /* Avoid expensive walking of rexmit queue if possible */
+ if (tp->retrans_out > 1)
+ return 0;
+
+ skb = tcp_write_queue_head(sk);
+ if (tcp_skb_is_last(sk, skb))
+ return 1;
+ skb = tcp_write_queue_next(sk, skb); /* Skips head */
+ tcp_for_write_queue_from(skb, sk) {
+ if (skb == tcp_send_head(sk))
+ break;
+ if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
+ return 0;
+ /* Short-circuit when first non-SACKed skb has been checked */
+ if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
+ break;
+ }
+ return 1;
+}
+
+/* RTO occurred, but do not yet enter Loss state. Instead, defer RTO
+ * recovery a bit and use heuristics in tcp_process_frto() to detect if
+ * the RTO was spurious. Only clear SACKED_RETRANS of the head here to
+ * keep retrans_out counting accurate (with SACK F-RTO, other than head
+ * may still have that bit set); TCPCB_LOST and remaining SACKED_RETRANS
+ * bits are handled if the Loss state is really to be entered (in
+ * tcp_enter_frto_loss).
+ *
+ * Do like tcp_enter_loss() would; when RTO expires the second time it
+ * does:
+ * "Reduce ssthresh if it has not yet been made inside this window."
+ */
+void tcp_enter_frto(struct sock *sk)
+{
+ const struct inet_connection_sock *icsk = inet_csk(sk);
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct sk_buff *skb;
+
+ if ((!tp->frto_counter && icsk->icsk_ca_state <= TCP_CA_Disorder) ||
+ tp->snd_una == tp->high_seq ||
+ ((icsk->icsk_ca_state == TCP_CA_Loss || tp->frto_counter) &&
+ !icsk->icsk_retransmits)) {
+ tp->prior_ssthresh = tcp_current_ssthresh(sk);
+ /* Our state is too optimistic in ssthresh() call because cwnd
+ * is not reduced until tcp_enter_frto_loss() when previous F-RTO
+ * recovery has not yet completed. Pattern would be this: RTO,
+ * Cumulative ACK, RTO (2xRTO for the same segment does not end
+ * up here twice).
+ * RFC4138 should be more specific on what to do, even though
+ * RTO is quite unlikely to occur after the first Cumulative ACK
+ * due to back-off and complexity of triggering events ...
+ */
+ if (tp->frto_counter) {
+ u32 stored_cwnd;
+ stored_cwnd = tp->snd_cwnd;
+ tp->snd_cwnd = 2;
+ tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
+ tp->snd_cwnd = stored_cwnd;
+ } else {
+ tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
+ }
+ /* ... in theory, cong.control module could do "any tricks" in
+ * ssthresh(), which means that ca_state, lost bits and lost_out
+ * counter would have to be faked before the call occurs. We
+ * consider that too expensive, unlikely and hacky, so modules
+ * using these in ssthresh() must deal these incompatibility
+ * issues if they receives CA_EVENT_FRTO and frto_counter != 0
+ */
+ tcp_ca_event(sk, CA_EVENT_FRTO);
+ }
+
+ tp->undo_marker = tp->snd_una;
+ tp->undo_retrans = 0;
+
+ skb = tcp_write_queue_head(sk);
+ if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
+ tp->undo_marker = 0;
+ if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
+ TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
+ tp->retrans_out -= tcp_skb_pcount(skb);
+ }
+ tcp_verify_left_out(tp);
+
+ /* Too bad if TCP was application limited */
+ tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp) + 1);
+
+ /* Earlier loss recovery underway (see RFC4138; Appendix B).
+ * The last condition is necessary at least in tp->frto_counter case.
+ */
+ if (tcp_is_sackfrto(tp) && (tp->frto_counter ||
+ ((1 << icsk->icsk_ca_state) & (TCPF_CA_Recovery|TCPF_CA_Loss))) &&
+ after(tp->high_seq, tp->snd_una)) {
+ tp->frto_highmark = tp->high_seq;
+ } else {
+ tp->frto_highmark = tp->snd_nxt;
+ }
+ tcp_set_ca_state(sk, TCP_CA_Disorder);
+ tp->high_seq = tp->snd_nxt;
+ tp->frto_counter = 1;
+}
+
+/* Enter Loss state after F-RTO was applied. Dupack arrived after RTO,
+ * which indicates that we should follow the traditional RTO recovery,
+ * i.e. mark everything lost and do go-back-N retransmission.
+ */
+static void tcp_enter_frto_loss(struct sock *sk, int allowed_segments, int flag)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct sk_buff *skb;
+
+ tp->lost_out = 0;
+ tp->retrans_out = 0;
+ if (tcp_is_reno(tp))
+ tcp_reset_reno_sack(tp);
+
+ tcp_for_write_queue(skb, sk) {
+ if (skb == tcp_send_head(sk))
+ break;
+
+ TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
+ /*
+ * Count the retransmission made on RTO correctly (only when
+ * waiting for the first ACK and did not get it)...
+ */
+ if ((tp->frto_counter == 1) && !(flag & FLAG_DATA_ACKED)) {
+ /* For some reason this R-bit might get cleared? */
+ if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
+ tp->retrans_out += tcp_skb_pcount(skb);
+ /* ...enter this if branch just for the first segment */
+ flag |= FLAG_DATA_ACKED;
+ } else {
+ if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
+ tp->undo_marker = 0;
+ TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
+ }
+
+ /* Marking forward transmissions that were made after RTO lost
+ * can cause unnecessary retransmissions in some scenarios,
+ * SACK blocks will mitigate that in some but not in all cases.
+ * We used to not mark them but it was causing break-ups with
+ * receivers that do only in-order receival.
+ *
+ * TODO: we could detect presence of such receiver and select
+ * different behavior per flow.
+ */
+ if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
+ TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
+ tp->lost_out += tcp_skb_pcount(skb);
+ tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
+ }
+ }
+ tcp_verify_left_out(tp);
+
+ tp->snd_cwnd = tcp_packets_in_flight(tp) + allowed_segments;
+ tp->snd_cwnd_cnt = 0;
+ tp->snd_cwnd_stamp = tcp_time_stamp;
+ tp->frto_counter = 0;
+ tp->bytes_acked = 0;
+
+ tp->reordering = min_t(unsigned int, tp->reordering,
+ sysctl_tcp_reordering);
+ tcp_set_ca_state(sk, TCP_CA_Loss);
+ tp->high_seq = tp->snd_nxt;
+ TCP_ECN_queue_cwr(tp);
+
+ tcp_clear_all_retrans_hints(tp);
+}
+
+static void tcp_clear_retrans_partial(struct tcp_sock *tp)
+{
+ tp->retrans_out = 0;
+ tp->lost_out = 0;
+
+ tp->undo_marker = 0;
+ tp->undo_retrans = -1;
+}
+
+void tcp_clear_retrans(struct tcp_sock *tp)
+{
+ tcp_clear_retrans_partial(tp);
+
+ tp->fackets_out = 0;
+ tp->sacked_out = 0;
+}
+
+/* Enter Loss state. If "how" is not zero, forget all SACK information
+ * and reset tags completely, otherwise preserve SACKs. If receiver
+ * dropped its ofo queue, we will know this due to reneging detection.
+ */
+void tcp_enter_loss(struct sock *sk, int how)
+{
+ const struct inet_connection_sock *icsk = inet_csk(sk);
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct sk_buff *skb;
+
+ /* Reduce ssthresh if it has not yet been made inside this window. */
+ if (icsk->icsk_ca_state <= TCP_CA_Disorder || tp->snd_una == tp->high_seq ||
+ (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
+ tp->prior_ssthresh = tcp_current_ssthresh(sk);
+ tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
+ tcp_ca_event(sk, CA_EVENT_LOSS);
+ }
+ tp->snd_cwnd = 1;
+ tp->snd_cwnd_cnt = 0;
+ tp->snd_cwnd_stamp = tcp_time_stamp;
+
+ tp->bytes_acked = 0;
+ tcp_clear_retrans_partial(tp);
+
+ if (tcp_is_reno(tp))
+ tcp_reset_reno_sack(tp);
+
+ tp->undo_marker = tp->snd_una;
+ if (how) {
+ tp->sacked_out = 0;
+ tp->fackets_out = 0;
+ }
+ tcp_clear_all_retrans_hints(tp);
+
+ tcp_for_write_queue(skb, sk) {
+ if (skb == tcp_send_head(sk))
+ break;
+
+ if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
+ tp->undo_marker = 0;
+ TCP_SKB_CB(skb)->sacked &= (~TCPCB_TAGBITS)|TCPCB_SACKED_ACKED;
+ if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || how) {
+ TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
+ TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
+ tp->lost_out += tcp_skb_pcount(skb);
+ tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
+ }
+ }
+ tcp_verify_left_out(tp);
+
+ tp->reordering = min_t(unsigned int, tp->reordering,
+ sysctl_tcp_reordering);
+ tcp_set_ca_state(sk, TCP_CA_Loss);
+ tp->high_seq = tp->snd_nxt;
+ TCP_ECN_queue_cwr(tp);
+ /* Abort F-RTO algorithm if one is in progress */
+ tp->frto_counter = 0;
+}
+
+/* If ACK arrived pointing to a remembered SACK, it means that our
+ * remembered SACKs do not reflect real state of receiver i.e.
+ * receiver _host_ is heavily congested (or buggy).
+ *
+ * Do processing similar to RTO timeout.
+ */
+static int tcp_check_sack_reneging(struct sock *sk, int flag)
+{
+ if (flag & FLAG_SACK_RENEGING) {
+ struct inet_connection_sock *icsk = inet_csk(sk);
+ NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSACKRENEGING);
+
+ tcp_enter_loss(sk, 1);
+ icsk->icsk_retransmits++;
+ tcp_retransmit_skb(sk, tcp_write_queue_head(sk));
+ inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
+ icsk->icsk_rto, TCP_RTO_MAX);
+ return 1;
+ }
+ return 0;
+}
+
+static inline int tcp_fackets_out(const struct tcp_sock *tp)
+{
+ return tcp_is_reno(tp) ? tp->sacked_out + 1 : tp->fackets_out;
+}
+
+/* Heurestics to calculate number of duplicate ACKs. There's no dupACKs
+ * counter when SACK is enabled (without SACK, sacked_out is used for
+ * that purpose).
+ *
+ * Instead, with FACK TCP uses fackets_out that includes both SACKed
+ * segments up to the highest received SACK block so far and holes in
+ * between them.
+ *
+ * With reordering, holes may still be in flight, so RFC3517 recovery
+ * uses pure sacked_out (total number of SACKed segments) even though
+ * it violates the RFC that uses duplicate ACKs, often these are equal
+ * but when e.g. out-of-window ACKs or packet duplication occurs,
+ * they differ. Since neither occurs due to loss, TCP should really
+ * ignore them.
+ */
+static inline int tcp_dupack_heuristics(const struct tcp_sock *tp)
+{
+ return tcp_is_fack(tp) ? tp->fackets_out : tp->sacked_out + 1;
+}
+
+static inline int tcp_skb_timedout(const struct sock *sk,
+ const struct sk_buff *skb)
+{
+ return tcp_time_stamp - TCP_SKB_CB(skb)->when > inet_csk(sk)->icsk_rto;
+}
+
+static inline int tcp_head_timedout(const struct sock *sk)
+{
+ const struct tcp_sock *tp = tcp_sk(sk);
+
+ return tp->packets_out &&
+ tcp_skb_timedout(sk, tcp_write_queue_head(sk));
+}
+
+/* Linux NewReno/SACK/FACK/ECN state machine.
+ * --------------------------------------
+ *
+ * "Open" Normal state, no dubious events, fast path.
+ * "Disorder" In all the respects it is "Open",
+ * but requires a bit more attention. It is entered when
+ * we see some SACKs or dupacks. It is split of "Open"
+ * mainly to move some processing from fast path to slow one.
+ * "CWR" CWND was reduced due to some Congestion Notification event.
+ * It can be ECN, ICMP source quench, local device congestion.
+ * "Recovery" CWND was reduced, we are fast-retransmitting.
+ * "Loss" CWND was reduced due to RTO timeout or SACK reneging.
+ *
+ * tcp_fastretrans_alert() is entered:
+ * - each incoming ACK, if state is not "Open"
+ * - when arrived ACK is unusual, namely:
+ * * SACK
+ * * Duplicate ACK.
+ * * ECN ECE.
+ *
+ * Counting packets in flight is pretty simple.
+ *
+ * in_flight = packets_out - left_out + retrans_out
+ *
+ * packets_out is SND.NXT-SND.UNA counted in packets.
+ *
+ * retrans_out is number of retransmitted segments.
+ *
+ * left_out is number of segments left network, but not ACKed yet.
+ *
+ * left_out = sacked_out + lost_out
+ *
+ * sacked_out: Packets, which arrived to receiver out of order
+ * and hence not ACKed. With SACKs this number is simply
+ * amount of SACKed data. Even without SACKs
+ * it is easy to give pretty reliable estimate of this number,
+ * counting duplicate ACKs.
+ *
+ * lost_out: Packets lost by network. TCP has no explicit
+ * "loss notification" feedback from network (for now).
+ * It means that this number can be only _guessed_.
+ * Actually, it is the heuristics to predict lossage that
+ * distinguishes different algorithms.
+ *
+ * F.e. after RTO, when all the queue is considered as lost,
+ * lost_out = packets_out and in_flight = retrans_out.
+ *
+ * Essentially, we have now two algorithms counting
+ * lost packets.
+ *
+ * FACK: It is the simplest heuristics. As soon as we decided
+ * that something is lost, we decide that _all_ not SACKed
+ * packets until the most forward SACK are lost. I.e.
+ * lost_out = fackets_out - sacked_out and left_out = fackets_out.
+ * It is absolutely correct estimate, if network does not reorder
+ * packets. And it loses any connection to reality when reordering
+ * takes place. We use FACK by default until reordering
+ * is suspected on the path to this destination.
+ *
+ * NewReno: when Recovery is entered, we assume that one segment
+ * is lost (classic Reno). While we are in Recovery and
+ * a partial ACK arrives, we assume that one more packet
+ * is lost (NewReno). This heuristics are the same in NewReno
+ * and SACK.
+ *
+ * Imagine, that's all! Forget about all this shamanism about CWND inflation
+ * deflation etc. CWND is real congestion window, never inflated, changes
+ * only according to classic VJ rules.
+ *
+ * Really tricky (and requiring careful tuning) part of algorithm
+ * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
+ * The first determines the moment _when_ we should reduce CWND and,
+ * hence, slow down forward transmission. In fact, it determines the moment
+ * when we decide that hole is caused by loss, rather than by a reorder.
+ *
+ * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
+ * holes, caused by lost packets.
+ *
+ * And the most logically complicated part of algorithm is undo
+ * heuristics. We detect false retransmits due to both too early
+ * fast retransmit (reordering) and underestimated RTO, analyzing
+ * timestamps and D-SACKs. When we detect that some segments were
+ * retransmitted by mistake and CWND reduction was wrong, we undo
+ * window reduction and abort recovery phase. This logic is hidden
+ * inside several functions named tcp_try_undo_<something>.
+ */
+
+/* This function decides, when we should leave Disordered state
+ * and enter Recovery phase, reducing congestion window.
+ *
+ * Main question: may we further continue forward transmission
+ * with the same cwnd?
+ */
+static int tcp_time_to_recover(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ __u32 packets_out;
+
+ /* Do not perform any recovery during F-RTO algorithm */
+ if (tp->frto_counter)
+ return 0;
+
+ /* Trick#1: The loss is proven. */
+ if (tp->lost_out)
+ return 1;
+
+ /* Not-A-Trick#2 : Classic rule... */
+ if (tcp_dupack_heuristics(tp) > tp->reordering)
+ return 1;
+
+ /* Trick#3 : when we use RFC2988 timer restart, fast
+ * retransmit can be triggered by timeout of queue head.
+ */
+ if (tcp_is_fack(tp) && tcp_head_timedout(sk))
+ return 1;
+
+ /* Trick#4: It is still not OK... But will it be useful to delay
+ * recovery more?
+ */
+ packets_out = tp->packets_out;
+ if (packets_out <= tp->reordering &&
+ tp->sacked_out >= max_t(__u32, packets_out/2, sysctl_tcp_reordering) &&
+ !tcp_may_send_now(sk)) {
+ /* We have nothing to send. This connection is limited
+ * either by receiver window or by application.
+ */
+ return 1;
+ }
+
+ /* If a thin stream is detected, retransmit after first
+ * received dupack. Employ only if SACK is supported in order
+ * to avoid possible corner-case series of spurious retransmissions
+ * Use only if there are no unsent data.
+ */
+ if ((tp->thin_dupack || sysctl_tcp_thin_dupack) &&
+ tcp_stream_is_thin(tp) && tcp_dupack_heuristics(tp) > 1 &&
+ tcp_is_sack(tp) && !tcp_send_head(sk))
+ return 1;
+
+ return 0;
+}
+
+/* New heuristics: it is possible only after we switched to restart timer
+ * each time when something is ACKed. Hence, we can detect timed out packets
+ * during fast retransmit without falling to slow start.
+ *
+ * Usefulness of this as is very questionable, since we should know which of
+ * the segments is the next to timeout which is relatively expensive to find
+ * in general case unless we add some data structure just for that. The
+ * current approach certainly won't find the right one too often and when it
+ * finally does find _something_ it usually marks large part of the window
+ * right away (because a retransmission with a larger timestamp blocks the
+ * loop from advancing). -ij
+ */
+static void tcp_timeout_skbs(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct sk_buff *skb;
+
+ if (!tcp_is_fack(tp) || !tcp_head_timedout(sk))
+ return;
+
+ skb = tp->scoreboard_skb_hint;
+ if (tp->scoreboard_skb_hint == NULL)
+ skb = tcp_write_queue_head(sk);
+
+ tcp_for_write_queue_from(skb, sk) {
+ if (skb == tcp_send_head(sk))
+ break;
+ if (!tcp_skb_timedout(sk, skb))
+ break;
+
+ tcp_skb_mark_lost(tp, skb);
+ }
+
+ tp->scoreboard_skb_hint = skb;
+
+ tcp_verify_left_out(tp);
+}
+
+/* Detect loss in event "A" above by marking head of queue up as lost.
+ * For FACK or non-SACK(Reno) senders, the first "packets" number of segments
+ * are considered lost. For RFC3517 SACK, a segment is considered lost if it
+ * has at least tp->reordering SACKed seqments above it; "packets" refers to
+ * the maximum SACKed segments to pass before reaching this limit.
+ */
+static void tcp_mark_head_lost(struct sock *sk, int packets, int mark_head)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct sk_buff *skb;
+ int cnt, oldcnt;
+ int err;
+ unsigned int mss;
+ /* Use SACK to deduce losses of new sequences sent during recovery */
+ const u32 loss_high = tcp_is_sack(tp) ? tp->snd_nxt : tp->high_seq;
+
+ WARN_ON(packets > tp->packets_out);
+ if (tp->lost_skb_hint) {
+ skb = tp->lost_skb_hint;
+ cnt = tp->lost_cnt_hint;
+ /* Head already handled? */
+ if (mark_head && skb != tcp_write_queue_head(sk))
+ return;
+ } else {
+ skb = tcp_write_queue_head(sk);
+ cnt = 0;
+ }
+
+ tcp_for_write_queue_from(skb, sk) {
+ if (skb == tcp_send_head(sk))
+ break;
+ /* TODO: do this better */
+ /* this is not the most efficient way to do this... */
+ tp->lost_skb_hint = skb;
+ tp->lost_cnt_hint = cnt;
+
+ if (after(TCP_SKB_CB(skb)->end_seq, loss_high))
+ break;
+
+ oldcnt = cnt;
+ if (tcp_is_fack(tp) || tcp_is_reno(tp) ||
+ (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
+ cnt += tcp_skb_pcount(skb);
+
+ if (cnt > packets) {
+ if ((tcp_is_sack(tp) && !tcp_is_fack(tp)) ||
+ (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) ||
+ (oldcnt >= packets))
+ break;
+
+ mss = skb_shinfo(skb)->gso_size;
+ err = tcp_fragment(sk, skb, (packets - oldcnt) * mss, mss);
+ if (err < 0)
+ break;
+ cnt = packets;
+ }
+
+ tcp_skb_mark_lost(tp, skb);
+
+ if (mark_head)
+ break;
+ }
+ tcp_verify_left_out(tp);
+}
+
+/* Account newly detected lost packet(s) */
+
+static void tcp_update_scoreboard(struct sock *sk, int fast_rexmit)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ if (tcp_is_reno(tp)) {
+ tcp_mark_head_lost(sk, 1, 1);
+ } else if (tcp_is_fack(tp)) {
+ int lost = tp->fackets_out - tp->reordering;
+ if (lost <= 0)
+ lost = 1;
+ tcp_mark_head_lost(sk, lost, 0);
+ } else {
+ int sacked_upto = tp->sacked_out - tp->reordering;
+ if (sacked_upto >= 0)
+ tcp_mark_head_lost(sk, sacked_upto, 0);
+ else if (fast_rexmit)
+ tcp_mark_head_lost(sk, 1, 1);
+ }
+
+ tcp_timeout_skbs(sk);
+}
+
+/* CWND moderation, preventing bursts due to too big ACKs
+ * in dubious situations.
+ */
+static inline void tcp_moderate_cwnd(struct tcp_sock *tp)
+{
+ tp->snd_cwnd = min(tp->snd_cwnd,
+ tcp_packets_in_flight(tp) + tcp_max_burst(tp));
+ tp->snd_cwnd_stamp = tcp_time_stamp;
+}
+
+/* Lower bound on congestion window is slow start threshold
+ * unless congestion avoidance choice decides to overide it.
+ */
+static inline u32 tcp_cwnd_min(const struct sock *sk)
+{
+ const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
+
+ return ca_ops->min_cwnd ? ca_ops->min_cwnd(sk) : tcp_sk(sk)->snd_ssthresh;
+}
+
+/* Decrease cwnd each second ack. */
+static void tcp_cwnd_down(struct sock *sk, int flag)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ int decr = tp->snd_cwnd_cnt + 1;
+
+ if ((flag & (FLAG_ANY_PROGRESS | FLAG_DSACKING_ACK)) ||
+ (tcp_is_reno(tp) && !(flag & FLAG_NOT_DUP))) {
+ tp->snd_cwnd_cnt = decr & 1;
+ decr >>= 1;
+
+ if (decr && tp->snd_cwnd > tcp_cwnd_min(sk))
+ tp->snd_cwnd -= decr;
+
+ tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp) + 1);
+ tp->snd_cwnd_stamp = tcp_time_stamp;
+ }
+}
+
+/* Nothing was retransmitted or returned timestamp is less
+ * than timestamp of the first retransmission.
+ */
+static inline int tcp_packet_delayed(const struct tcp_sock *tp)
+{
+ return !tp->retrans_stamp ||
+ (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
+ before(tp->rx_opt.rcv_tsecr, tp->retrans_stamp));
+}
+
+/* Undo procedures. */
+
+#if FASTRETRANS_DEBUG > 1
+static void DBGUNDO(struct sock *sk, const char *msg)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct inet_sock *inet = inet_sk(sk);
+
+ if (sk->sk_family == AF_INET) {
+ printk(KERN_DEBUG "Undo %s %pI4/%u c%u l%u ss%u/%u p%u\n",
+ msg,
+ &inet->inet_daddr, ntohs(inet->inet_dport),
+ tp->snd_cwnd, tcp_left_out(tp),
+ tp->snd_ssthresh, tp->prior_ssthresh,
+ tp->packets_out);
+ }
+#if IS_ENABLED(CONFIG_IPV6)
+ else if (sk->sk_family == AF_INET6) {
+ struct ipv6_pinfo *np = inet6_sk(sk);
+ printk(KERN_DEBUG "Undo %s %pI6/%u c%u l%u ss%u/%u p%u\n",
+ msg,
+ &np->daddr, ntohs(inet->inet_dport),
+ tp->snd_cwnd, tcp_left_out(tp),
+ tp->snd_ssthresh, tp->prior_ssthresh,
+ tp->packets_out);
+ }
+#endif
+}
+#else
+#define DBGUNDO(x...) do { } while (0)
+#endif
+
+static void tcp_undo_cwr(struct sock *sk, const bool undo_ssthresh)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ if (tp->prior_ssthresh) {
+ const struct inet_connection_sock *icsk = inet_csk(sk);
+
+ if (icsk->icsk_ca_ops->undo_cwnd)
+ tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);
+ else
+ tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh << 1);
+
+ if (undo_ssthresh && tp->prior_ssthresh > tp->snd_ssthresh) {
+ tp->snd_ssthresh = tp->prior_ssthresh;
+ TCP_ECN_withdraw_cwr(tp);
+ }
+ } else {
+ tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh);
+ }
+ tp->snd_cwnd_stamp = tcp_time_stamp;
+}
+
+static inline int tcp_may_undo(const struct tcp_sock *tp)
+{
+ return tp->undo_marker && (!tp->undo_retrans || tcp_packet_delayed(tp));
+}
+
+/* People celebrate: "We love our President!" */
+static int tcp_try_undo_recovery(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ if (tcp_may_undo(tp)) {
+ int mib_idx;
+
+ /* Happy end! We did not retransmit anything
+ * or our original transmission succeeded.
+ */
+ DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
+ tcp_undo_cwr(sk, true);
+ if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
+ mib_idx = LINUX_MIB_TCPLOSSUNDO;
+ else
+ mib_idx = LINUX_MIB_TCPFULLUNDO;
+
+ NET_INC_STATS_BH(sock_net(sk), mib_idx);
+ tp->undo_marker = 0;
+ }
+ if (tp->snd_una == tp->high_seq && tcp_is_reno(tp)) {
+ /* Hold old state until something *above* high_seq
+ * is ACKed. For Reno it is MUST to prevent false
+ * fast retransmits (RFC2582). SACK TCP is safe. */
+ tcp_moderate_cwnd(tp);
+ return 1;
+ }
+ tcp_set_ca_state(sk, TCP_CA_Open);
+ return 0;
+}
+
+/* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
+static void tcp_try_undo_dsack(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ if (tp->undo_marker && !tp->undo_retrans) {
+ DBGUNDO(sk, "D-SACK");
+ tcp_undo_cwr(sk, true);
+ tp->undo_marker = 0;
+ NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDSACKUNDO);
+ }
+}
+
+/* We can clear retrans_stamp when there are no retransmissions in the
+ * window. It would seem that it is trivially available for us in
+ * tp->retrans_out, however, that kind of assumptions doesn't consider
+ * what will happen if errors occur when sending retransmission for the
+ * second time. ...It could the that such segment has only
+ * TCPCB_EVER_RETRANS set at the present time. It seems that checking
+ * the head skb is enough except for some reneging corner cases that
+ * are not worth the effort.
+ *
+ * Main reason for all this complexity is the fact that connection dying
+ * time now depends on the validity of the retrans_stamp, in particular,
+ * that successive retransmissions of a segment must not advance
+ * retrans_stamp under any conditions.
+ */
+static int tcp_any_retrans_done(const struct sock *sk)
+{
+ const struct tcp_sock *tp = tcp_sk(sk);
+ struct sk_buff *skb;
+
+ if (tp->retrans_out)
+ return 1;
+
+ skb = tcp_write_queue_head(sk);
+ if (unlikely(skb && TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS))
+ return 1;
+
+ return 0;
+}
+
+/* Undo during fast recovery after partial ACK. */
+
+static int tcp_try_undo_partial(struct sock *sk, int acked)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ /* Partial ACK arrived. Force Hoe's retransmit. */
+ int failed = tcp_is_reno(tp) || (tcp_fackets_out(tp) > tp->reordering);
+
+ if (tcp_may_undo(tp)) {
+ /* Plain luck! Hole if filled with delayed
+ * packet, rather than with a retransmit.
+ */
+ if (!tcp_any_retrans_done(sk))
+ tp->retrans_stamp = 0;
+
+ tcp_update_reordering(sk, tcp_fackets_out(tp) + acked, 1);
+
+ DBGUNDO(sk, "Hoe");
+ tcp_undo_cwr(sk, false);
+ NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO);
+
+ /* So... Do not make Hoe's retransmit yet.
+ * If the first packet was delayed, the rest
+ * ones are most probably delayed as well.
+ */
+ failed = 0;
+ }
+ return failed;
+}
+
+/* Undo during loss recovery after partial ACK. */
+static int tcp_try_undo_loss(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ if (tcp_may_undo(tp)) {
+ struct sk_buff *skb;
+ tcp_for_write_queue(skb, sk) {
+ if (skb == tcp_send_head(sk))
+ break;
+ TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
+ }
+
+ tcp_clear_all_retrans_hints(tp);
+
+ DBGUNDO(sk, "partial loss");
+ tp->lost_out = 0;
+ tcp_undo_cwr(sk, true);
+ NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSSUNDO);
+ inet_csk(sk)->icsk_retransmits = 0;
+ tp->undo_marker = 0;
+ if (tcp_is_sack(tp))
+ tcp_set_ca_state(sk, TCP_CA_Open);
+ return 1;
+ }
+ return 0;
+}
+
+static inline void tcp_complete_cwr(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ /* Do not moderate cwnd if it's already undone in cwr or recovery. */
+ if (tp->undo_marker) {
+ if (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR) {
+ tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
+ tp->snd_cwnd_stamp = tcp_time_stamp;
+ } else if (tp->snd_ssthresh < TCP_INFINITE_SSTHRESH) {
+ /* PRR algorithm. */
+ tp->snd_cwnd = tp->snd_ssthresh;
+ tp->snd_cwnd_stamp = tcp_time_stamp;
+ }
+ }
+ tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
+}
+
+static void tcp_try_keep_open(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ int state = TCP_CA_Open;
+
+ if (tcp_left_out(tp) || tcp_any_retrans_done(sk))
+ state = TCP_CA_Disorder;
+
+ if (inet_csk(sk)->icsk_ca_state != state) {
+ tcp_set_ca_state(sk, state);
+ tp->high_seq = tp->snd_nxt;
+ }
+}
+
+static void tcp_try_to_open(struct sock *sk, int flag)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ tcp_verify_left_out(tp);
+
+ if (!tp->frto_counter && !tcp_any_retrans_done(sk))
+ tp->retrans_stamp = 0;
+
+ if (flag & FLAG_ECE)
+ tcp_enter_cwr(sk, 1);
+
+ if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
+ tcp_try_keep_open(sk);
+ if (inet_csk(sk)->icsk_ca_state != TCP_CA_Open)
+ tcp_moderate_cwnd(tp);
+ } else {
+ tcp_cwnd_down(sk, flag);
+ }
+}
+
+static void tcp_mtup_probe_failed(struct sock *sk)
+{
+ struct inet_connection_sock *icsk = inet_csk(sk);
+
+ icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;
+ icsk->icsk_mtup.probe_size = 0;
+}
+
+static void tcp_mtup_probe_success(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct inet_connection_sock *icsk = inet_csk(sk);
+
+ /* FIXME: breaks with very large cwnd */
+ tp->prior_ssthresh = tcp_current_ssthresh(sk);
+ tp->snd_cwnd = tp->snd_cwnd *
+ tcp_mss_to_mtu(sk, tp->mss_cache) /
+ icsk->icsk_mtup.probe_size;
+ tp->snd_cwnd_cnt = 0;
+ tp->snd_cwnd_stamp = tcp_time_stamp;
+ tp->snd_ssthresh = tcp_current_ssthresh(sk);
+
+ icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
+ icsk->icsk_mtup.probe_size = 0;
+ tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
+}
+
+/* Do a simple retransmit without using the backoff mechanisms in
+ * tcp_timer. This is used for path mtu discovery.
+ * The socket is already locked here.
+ */
+void tcp_simple_retransmit(struct sock *sk)
+{
+ const struct inet_connection_sock *icsk = inet_csk(sk);
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct sk_buff *skb;
+ unsigned int mss = tcp_current_mss(sk);
+ u32 prior_lost = tp->lost_out;
+
+ tcp_for_write_queue(skb, sk) {
+ if (skb == tcp_send_head(sk))
+ break;
+ if (tcp_skb_seglen(skb) > mss &&
+ !(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
+ if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
+ TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
+ tp->retrans_out -= tcp_skb_pcount(skb);
+ }
+ tcp_skb_mark_lost_uncond_verify(tp, skb);
+ }
+ }
+
+ tcp_clear_retrans_hints_partial(tp);
+
+ if (prior_lost == tp->lost_out)
+ return;
+
+ if (tcp_is_reno(tp))
+ tcp_limit_reno_sacked(tp);
+
+ tcp_verify_left_out(tp);
+
+ /* Don't muck with the congestion window here.
+ * Reason is that we do not increase amount of _data_
+ * in network, but units changed and effective
+ * cwnd/ssthresh really reduced now.
+ */
+ if (icsk->icsk_ca_state != TCP_CA_Loss) {
+ tp->high_seq = tp->snd_nxt;
+ tp->snd_ssthresh = tcp_current_ssthresh(sk);
+ tp->prior_ssthresh = 0;
+ tp->undo_marker = 0;
+ tcp_set_ca_state(sk, TCP_CA_Loss);
+ }
+ tcp_xmit_retransmit_queue(sk);
+}
+EXPORT_SYMBOL(tcp_simple_retransmit);
+
+/* This function implements the PRR algorithm, specifcally the PRR-SSRB
+ * (proportional rate reduction with slow start reduction bound) as described in
+ * http://www.ietf.org/id/draft-mathis-tcpm-proportional-rate-reduction-01.txt.
+ * It computes the number of packets to send (sndcnt) based on packets newly
+ * delivered:
+ * 1) If the packets in flight is larger than ssthresh, PRR spreads the
+ * cwnd reductions across a full RTT.
+ * 2) If packets in flight is lower than ssthresh (such as due to excess
+ * losses and/or application stalls), do not perform any further cwnd
+ * reductions, but instead slow start up to ssthresh.
+ */
+static void tcp_update_cwnd_in_recovery(struct sock *sk, int newly_acked_sacked,
+ int fast_rexmit, int flag)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ int sndcnt = 0;
+ int delta = tp->snd_ssthresh - tcp_packets_in_flight(tp);
+ if (newly_acked_sacked <= 0 || WARN_ON_ONCE(!tp->prior_cwnd))
+ return;
+
+ if (tcp_packets_in_flight(tp) > tp->snd_ssthresh) {
+ u64 dividend = (u64)tp->snd_ssthresh * tp->prr_delivered +
+ tp->prior_cwnd - 1;
+ sndcnt = div_u64(dividend, tp->prior_cwnd) - tp->prr_out;
+ } else {
+ sndcnt = min_t(int, delta,
+ max_t(int, tp->prr_delivered - tp->prr_out,
+ newly_acked_sacked) + 1);
+ }
+
+ sndcnt = max(sndcnt, (fast_rexmit ? 1 : 0));
+ tp->snd_cwnd = tcp_packets_in_flight(tp) + sndcnt;
+}
+
+/* Process an event, which can update packets-in-flight not trivially.
+ * Main goal of this function is to calculate new estimate for left_out,
+ * taking into account both packets sitting in receiver's buffer and
+ * packets lost by network.
+ *
+ * Besides that it does CWND reduction, when packet loss is detected
+ * and changes state of machine.
+ *
+ * It does _not_ decide what to send, it is made in function
+ * tcp_xmit_retransmit_queue().
+ */
+static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked,
+ int prior_sacked, int prior_packets,
+ bool is_dupack, int flag)
+{
+ struct inet_connection_sock *icsk = inet_csk(sk);
+ struct tcp_sock *tp = tcp_sk(sk);
+ int do_lost = is_dupack || ((flag & FLAG_DATA_SACKED) &&
+ (tcp_fackets_out(tp) > tp->reordering));
+ int newly_acked_sacked = 0;
+ int fast_rexmit = 0, mib_idx;
+
+ if (WARN_ON(!tp->packets_out && tp->sacked_out))
+ tp->sacked_out = 0;
+ if (WARN_ON(!tp->sacked_out && tp->fackets_out))
+ tp->fackets_out = 0;
+
+ /* Now state machine starts.
+ * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
+ if (flag & FLAG_ECE)
+ tp->prior_ssthresh = 0;
+
+ /* B. In all the states check for reneging SACKs. */
+ if (tcp_check_sack_reneging(sk, flag))
+ return;
+
+ /* C. Check consistency of the current state. */
+ tcp_verify_left_out(tp);
+
+ /* D. Check state exit conditions. State can be terminated
+ * when high_seq is ACKed. */
+ if (icsk->icsk_ca_state == TCP_CA_Open) {
+ WARN_ON(tp->retrans_out != 0);
+ tp->retrans_stamp = 0;
+ } else if (!before(tp->snd_una, tp->high_seq)) {
+ switch (icsk->icsk_ca_state) {
+ case TCP_CA_Loss:
+ icsk->icsk_retransmits = 0;
+ if (tcp_try_undo_recovery(sk))
+ return;
+ break;
+
+ case TCP_CA_CWR:
+ /* CWR is to be held something *above* high_seq
+ * is ACKed for CWR bit to reach receiver. */
+ if (tp->snd_una != tp->high_seq) {
+ tcp_complete_cwr(sk);
+ tcp_set_ca_state(sk, TCP_CA_Open);
+ }
+ break;
+
+ case TCP_CA_Recovery:
+ if (tcp_is_reno(tp))
+ tcp_reset_reno_sack(tp);
+ if (tcp_try_undo_recovery(sk))
+ return;
+ tcp_complete_cwr(sk);
+ break;
+ }
+ }
+
+ /* E. Process state. */
+ switch (icsk->icsk_ca_state) {
+ case TCP_CA_Recovery:
+ if (!(flag & FLAG_SND_UNA_ADVANCED)) {
+ if (tcp_is_reno(tp) && is_dupack)
+ tcp_add_reno_sack(sk);
+ } else
+ do_lost = tcp_try_undo_partial(sk, pkts_acked);
+ newly_acked_sacked = prior_packets - tp->packets_out +
+ tp->sacked_out - prior_sacked;
+ break;
+ case TCP_CA_Loss:
+ if (flag & FLAG_DATA_ACKED)
+ icsk->icsk_retransmits = 0;
+ if (tcp_is_reno(tp) && flag & FLAG_SND_UNA_ADVANCED)
+ tcp_reset_reno_sack(tp);
+ if (!tcp_try_undo_loss(sk)) {
+ tcp_moderate_cwnd(tp);
+ tcp_xmit_retransmit_queue(sk);
+ return;
+ }
+ if (icsk->icsk_ca_state != TCP_CA_Open)
+ return;
+ /* Loss is undone; fall through to processing in Open state. */
+ default:
+ if (tcp_is_reno(tp)) {
+ if (flag & FLAG_SND_UNA_ADVANCED)
+ tcp_reset_reno_sack(tp);
+ if (is_dupack)
+ tcp_add_reno_sack(sk);
+ }
+ newly_acked_sacked = prior_packets - tp->packets_out +
+ tp->sacked_out - prior_sacked;
+
+ if (icsk->icsk_ca_state <= TCP_CA_Disorder)
+ tcp_try_undo_dsack(sk);
+
+ if (!tcp_time_to_recover(sk)) {
+ tcp_try_to_open(sk, flag);
+ return;
+ }
+
+ /* MTU probe failure: don't reduce cwnd */
+ if (icsk->icsk_ca_state < TCP_CA_CWR &&
+ icsk->icsk_mtup.probe_size &&
+ tp->snd_una == tp->mtu_probe.probe_seq_start) {
+ tcp_mtup_probe_failed(sk);
+ /* Restores the reduction we did in tcp_mtup_probe() */
+ tp->snd_cwnd++;
+ tcp_simple_retransmit(sk);
+ return;
+ }
+
+ /* Otherwise enter Recovery state */
+
+ if (tcp_is_reno(tp))
+ mib_idx = LINUX_MIB_TCPRENORECOVERY;
+ else
+ mib_idx = LINUX_MIB_TCPSACKRECOVERY;
+
+ NET_INC_STATS_BH(sock_net(sk), mib_idx);
+
+ tp->high_seq = tp->snd_nxt;
+ tp->prior_ssthresh = 0;
+ tp->undo_marker = tp->snd_una;
+ tp->undo_retrans = tp->retrans_out ? : -1;
+
+ if (icsk->icsk_ca_state < TCP_CA_CWR) {
+ if (!(flag & FLAG_ECE))
+ tp->prior_ssthresh = tcp_current_ssthresh(sk);
+ tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
+ TCP_ECN_queue_cwr(tp);
+ }
+
+ tp->bytes_acked = 0;
+ tp->snd_cwnd_cnt = 0;
+ tp->prior_cwnd = tp->snd_cwnd;
+ tp->prr_delivered = 0;
+ tp->prr_out = 0;
+ tcp_set_ca_state(sk, TCP_CA_Recovery);
+ fast_rexmit = 1;
+ }
+
+ if (do_lost || (tcp_is_fack(tp) && tcp_head_timedout(sk)))
+ tcp_update_scoreboard(sk, fast_rexmit);
+ tp->prr_delivered += newly_acked_sacked;
+ tcp_update_cwnd_in_recovery(sk, newly_acked_sacked, fast_rexmit, flag);
+ tcp_xmit_retransmit_queue(sk);
+}
+
+void tcp_valid_rtt_meas(struct sock *sk, u32 seq_rtt)
+{
+ tcp_rtt_estimator(sk, seq_rtt);
+ tcp_set_rto(sk);
+ inet_csk(sk)->icsk_backoff = 0;
+}
+EXPORT_SYMBOL(tcp_valid_rtt_meas);
+
+/* Read draft-ietf-tcplw-high-performance before mucking
+ * with this code. (Supersedes RFC1323)
+ */
+static void tcp_ack_saw_tstamp(struct sock *sk, int flag)
+{
+ /* RTTM Rule: A TSecr value received in a segment is used to
+ * update the averaged RTT measurement only if the segment
+ * acknowledges some new data, i.e., only if it advances the
+ * left edge of the send window.
+ *
+ * See draft-ietf-tcplw-high-performance-00, section 3.3.
+ * 1998/04/10 Andrey V. Savochkin <saw@msu.ru>
+ *
+ * Changed: reset backoff as soon as we see the first valid sample.
+ * If we do not, we get strongly overestimated rto. With timestamps
+ * samples are accepted even from very old segments: f.e., when rtt=1
+ * increases to 8, we retransmit 5 times and after 8 seconds delayed
+ * answer arrives rto becomes 120 seconds! If at least one of segments
+ * in window is lost... Voila. --ANK (010210)
+ */
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ tcp_valid_rtt_meas(sk, tcp_time_stamp - tp->rx_opt.rcv_tsecr);
+}
+
+static void tcp_ack_no_tstamp(struct sock *sk, u32 seq_rtt, int flag)
+{
+ /* We don't have a timestamp. Can only use
+ * packets that are not retransmitted to determine
+ * rtt estimates. Also, we must not reset the
+ * backoff for rto until we get a non-retransmitted
+ * packet. This allows us to deal with a situation
+ * where the network delay has increased suddenly.
+ * I.e. Karn's algorithm. (SIGCOMM '87, p5.)
+ */
+
+ if (flag & FLAG_RETRANS_DATA_ACKED)
+ return;
+
+ tcp_valid_rtt_meas(sk, seq_rtt);
+}
+
+static inline void tcp_ack_update_rtt(struct sock *sk, const int flag,
+ const s32 seq_rtt)
+{
+ const struct tcp_sock *tp = tcp_sk(sk);
+ /* Note that peer MAY send zero echo. In this case it is ignored. (rfc1323) */
+ if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
+ tcp_ack_saw_tstamp(sk, flag);
+ else if (seq_rtt >= 0)
+ tcp_ack_no_tstamp(sk, seq_rtt, flag);
+}
+
+static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
+{
+ const struct inet_connection_sock *icsk = inet_csk(sk);
+ icsk->icsk_ca_ops->cong_avoid(sk, ack, in_flight);
+ tcp_sk(sk)->snd_cwnd_stamp = tcp_time_stamp;
+}
+
+/* Restart timer after forward progress on connection.
+ * RFC2988 recommends to restart timer to now+rto.
+ */
+static void tcp_rearm_rto(struct sock *sk)
+{
+ const struct tcp_sock *tp = tcp_sk(sk);
+
+ if (!tp->packets_out) {
+ inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
+ } else {
+ inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
+ inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
+ }
+}
+
+/* If we get here, the whole TSO packet has not been acked. */
+static u32 tcp_tso_acked(struct sock *sk, struct sk_buff *skb)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ u32 packets_acked;
+
+ BUG_ON(!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una));
+
+ packets_acked = tcp_skb_pcount(skb);
+ if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
+ return 0;
+ packets_acked -= tcp_skb_pcount(skb);
+
+ if (packets_acked) {
+ BUG_ON(tcp_skb_pcount(skb) == 0);
+ BUG_ON(!before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq));
+ }
+
+ return packets_acked;
+}
+
+/* Remove acknowledged frames from the retransmission queue. If our packet
+ * is before the ack sequence we can discard it as it's confirmed to have
+ * arrived at the other end.
+ */
+static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
+ u32 prior_snd_una)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ const struct inet_connection_sock *icsk = inet_csk(sk);
+ struct sk_buff *skb;
+ u32 now = tcp_time_stamp;
+ int fully_acked = 1;
+ int flag = 0;
+ u32 pkts_acked = 0;
+ u32 reord = tp->packets_out;
+ u32 prior_sacked = tp->sacked_out;
+ s32 seq_rtt = -1;
+ s32 ca_seq_rtt = -1;
+ ktime_t last_ackt = net_invalid_timestamp();
+
+ while ((skb = tcp_write_queue_head(sk)) && skb != tcp_send_head(sk)) {
+ struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
+ u32 acked_pcount;
+ u8 sacked = scb->sacked;
+
+ /* Determine how many packets and what bytes were acked, tso and else */
+ if (after(scb->end_seq, tp->snd_una)) {
+ if (tcp_skb_pcount(skb) == 1 ||
+ !after(tp->snd_una, scb->seq))
+ break;
+
+ acked_pcount = tcp_tso_acked(sk, skb);
+ if (!acked_pcount)
+ break;
+
+ fully_acked = 0;
+ } else {
+ acked_pcount = tcp_skb_pcount(skb);
+ }
+
+ if (sacked & TCPCB_RETRANS) {
+ if (sacked & TCPCB_SACKED_RETRANS)
+ tp->retrans_out -= acked_pcount;
+ flag |= FLAG_RETRANS_DATA_ACKED;
+ ca_seq_rtt = -1;
+ seq_rtt = -1;
+ if ((flag & FLAG_DATA_ACKED) || (acked_pcount > 1))
+ flag |= FLAG_NONHEAD_RETRANS_ACKED;
+ } else {
+ ca_seq_rtt = now - scb->when;
+ last_ackt = skb->tstamp;
+ if (seq_rtt < 0) {
+ seq_rtt = ca_seq_rtt;
+ }
+ if (!(sacked & TCPCB_SACKED_ACKED))
+ reord = min(pkts_acked, reord);
+ }
+
+ if (sacked & TCPCB_SACKED_ACKED)
+ tp->sacked_out -= acked_pcount;
+ if (sacked & TCPCB_LOST)
+ tp->lost_out -= acked_pcount;
+
+ tp->packets_out -= acked_pcount;
+ pkts_acked += acked_pcount;
+
+ /* Initial outgoing SYN's get put onto the write_queue
+ * just like anything else we transmit. It is not
+ * true data, and if we misinform our callers that
+ * this ACK acks real data, we will erroneously exit
+ * connection startup slow start one packet too
+ * quickly. This is severely frowned upon behavior.
+ */
+ if (!(scb->tcp_flags & TCPHDR_SYN)) {
+ flag |= FLAG_DATA_ACKED;
+ } else {
+ flag |= FLAG_SYN_ACKED;
+ tp->retrans_stamp = 0;
+ }
+
+ if (!fully_acked)
+ break;
+
+ tcp_unlink_write_queue(skb, sk);
+ sk_wmem_free_skb(sk, skb);
+ tp->scoreboard_skb_hint = NULL;
+ if (skb == tp->retransmit_skb_hint)
+ tp->retransmit_skb_hint = NULL;
+ if (skb == tp->lost_skb_hint)
+ tp->lost_skb_hint = NULL;
+ }
+
+ if (likely(between(tp->snd_up, prior_snd_una, tp->snd_una)))
+ tp->snd_up = tp->snd_una;
+
+ if (skb && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
+ flag |= FLAG_SACK_RENEGING;
+
+ if (flag & FLAG_ACKED) {
+ const struct tcp_congestion_ops *ca_ops
+ = inet_csk(sk)->icsk_ca_ops;
+
+ if (unlikely(icsk->icsk_mtup.probe_size &&
+ !after(tp->mtu_probe.probe_seq_end, tp->snd_una))) {
+ tcp_mtup_probe_success(sk);
+ }
+
+ tcp_ack_update_rtt(sk, flag, seq_rtt);
+ tcp_rearm_rto(sk);
+
+ if (tcp_is_reno(tp)) {
+ tcp_remove_reno_sacks(sk, pkts_acked);
+ } else {
+ int delta;
+
+ /* Non-retransmitted hole got filled? That's reordering */
+ if (reord < prior_fackets)
+ tcp_update_reordering(sk, tp->fackets_out - reord, 0);
+
+ delta = tcp_is_fack(tp) ? pkts_acked :
+ prior_sacked - tp->sacked_out;
+ tp->lost_cnt_hint -= min(tp->lost_cnt_hint, delta);
+ }
+
+ tp->fackets_out -= min(pkts_acked, tp->fackets_out);
+
+ if (ca_ops->pkts_acked) {
+ s32 rtt_us = -1;
+
+ /* Is the ACK triggering packet unambiguous? */
+ if (!(flag & FLAG_RETRANS_DATA_ACKED)) {
+ /* High resolution needed and available? */
+ if (ca_ops->flags & TCP_CONG_RTT_STAMP &&
+ !ktime_equal(last_ackt,
+ net_invalid_timestamp()))
+ rtt_us = ktime_us_delta(ktime_get_real(),
+ last_ackt);
+ else if (ca_seq_rtt >= 0)
+ rtt_us = jiffies_to_usecs(ca_seq_rtt);
+ }
+
+ ca_ops->pkts_acked(sk, pkts_acked, rtt_us);
+ }
+ }
+
+#if FASTRETRANS_DEBUG > 0
+ WARN_ON((int)tp->sacked_out < 0);
+ WARN_ON((int)tp->lost_out < 0);
+ WARN_ON((int)tp->retrans_out < 0);
+ if (!tp->packets_out && tcp_is_sack(tp)) {
+ icsk = inet_csk(sk);
+ if (tp->lost_out) {
+ printk(KERN_DEBUG "Leak l=%u %d\n",
+ tp->lost_out, icsk->icsk_ca_state);
+ tp->lost_out = 0;
+ }
+ if (tp->sacked_out) {
+ printk(KERN_DEBUG "Leak s=%u %d\n",
+ tp->sacked_out, icsk->icsk_ca_state);
+ tp->sacked_out = 0;
+ }
+ if (tp->retrans_out) {
+ printk(KERN_DEBUG "Leak r=%u %d\n",
+ tp->retrans_out, icsk->icsk_ca_state);
+ tp->retrans_out = 0;
+ }
+ }
+#endif
+ return flag;
+}
+
+static void tcp_ack_probe(struct sock *sk)
+{
+ const struct tcp_sock *tp = tcp_sk(sk);
+ struct inet_connection_sock *icsk = inet_csk(sk);
+
+ /* Was it a usable window open? */
+
+ if (!after(TCP_SKB_CB(tcp_send_head(sk))->end_seq, tcp_wnd_end(tp))) {
+ icsk->icsk_backoff = 0;
+ inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
+ /* Socket must be waked up by subsequent tcp_data_snd_check().
+ * This function is not for random using!
+ */
+ } else {
+ inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
+ min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX),
+ TCP_RTO_MAX);
+ }
+}
+
+static inline int tcp_ack_is_dubious(const struct sock *sk, const int flag)
+{
+ return !(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
+ inet_csk(sk)->icsk_ca_state != TCP_CA_Open;
+}
+
+static inline int tcp_may_raise_cwnd(const struct sock *sk, const int flag)
+{
+ const struct tcp_sock *tp = tcp_sk(sk);
+ return (!(flag & FLAG_ECE) || tp->snd_cwnd < tp->snd_ssthresh) &&
+ !((1 << inet_csk(sk)->icsk_ca_state) & (TCPF_CA_Recovery | TCPF_CA_CWR));
+}
+
+/* Check that window update is acceptable.
+ * The function assumes that snd_una<=ack<=snd_next.
+ */
+static inline int tcp_may_update_window(const struct tcp_sock *tp,
+ const u32 ack, const u32 ack_seq,
+ const u32 nwin)
+{
+ return after(ack, tp->snd_una) ||
+ after(ack_seq, tp->snd_wl1) ||
+ (ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd);
+}
+
+/* Update our send window.
+ *
+ * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
+ * and in FreeBSD. NetBSD's one is even worse.) is wrong.
+ */
+static int tcp_ack_update_window(struct sock *sk, const struct sk_buff *skb, u32 ack,
+ u32 ack_seq)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ int flag = 0;
+ u32 nwin = ntohs(tcp_hdr(skb)->window);
+
+ if (likely(!tcp_hdr(skb)->syn))
+ nwin <<= tp->rx_opt.snd_wscale;
+
+ if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
+ flag |= FLAG_WIN_UPDATE;
+ tcp_update_wl(tp, ack_seq);
+
+ if (tp->snd_wnd != nwin) {
+ tp->snd_wnd = nwin;
+
+ /* Note, it is the only place, where
+ * fast path is recovered for sending TCP.
+ */
+ tp->pred_flags = 0;
+ tcp_fast_path_check(sk);
+
+ if (nwin > tp->max_window) {
+ tp->max_window = nwin;
+ tcp_sync_mss(sk, inet_csk(sk)->icsk_pmtu_cookie);
+ }
+ }
+ }
+
+ tp->snd_una = ack;
+
+ return flag;
+}
+
+/* A very conservative spurious RTO response algorithm: reduce cwnd and
+ * continue in congestion avoidance.
+ */
+static void tcp_conservative_spur_to_response(struct tcp_sock *tp)
+{
+ tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
+ tp->snd_cwnd_cnt = 0;
+ tp->bytes_acked = 0;
+ TCP_ECN_queue_cwr(tp);
+ tcp_moderate_cwnd(tp);
+}
+
+/* A conservative spurious RTO response algorithm: reduce cwnd using
+ * rate halving and continue in congestion avoidance.
+ */
+static void tcp_ratehalving_spur_to_response(struct sock *sk)
+{
+ tcp_enter_cwr(sk, 0);
+}
+
+static void tcp_undo_spur_to_response(struct sock *sk, int flag)
+{
+ if (flag & FLAG_ECE)
+ tcp_ratehalving_spur_to_response(sk);
+ else
+ tcp_undo_cwr(sk, true);
+}
+
+/* F-RTO spurious RTO detection algorithm (RFC4138)
+ *
+ * F-RTO affects during two new ACKs following RTO (well, almost, see inline
+ * comments). State (ACK number) is kept in frto_counter. When ACK advances
+ * window (but not to or beyond highest sequence sent before RTO):
+ * On First ACK, send two new segments out.
+ * On Second ACK, RTO was likely spurious. Do spurious response (response
+ * algorithm is not part of the F-RTO detection algorithm
+ * given in RFC4138 but can be selected separately).
+ * Otherwise (basically on duplicate ACK), RTO was (likely) caused by a loss
+ * and TCP falls back to conventional RTO recovery. F-RTO allows overriding
+ * of Nagle, this is done using frto_counter states 2 and 3, when a new data
+ * segment of any size sent during F-RTO, state 2 is upgraded to 3.
+ *
+ * Rationale: if the RTO was spurious, new ACKs should arrive from the
+ * original window even after we transmit two new data segments.
+ *
+ * SACK version:
+ * on first step, wait until first cumulative ACK arrives, then move to
+ * the second step. In second step, the next ACK decides.
+ *
+ * F-RTO is implemented (mainly) in four functions:
+ * - tcp_use_frto() is used to determine if TCP is can use F-RTO
+ * - tcp_enter_frto() prepares TCP state on RTO if F-RTO is used, it is
+ * called when tcp_use_frto() showed green light
+ * - tcp_process_frto() handles incoming ACKs during F-RTO algorithm
+ * - tcp_enter_frto_loss() is called if there is not enough evidence
+ * to prove that the RTO is indeed spurious. It transfers the control
+ * from F-RTO to the conventional RTO recovery
+ */
+static int tcp_process_frto(struct sock *sk, int flag)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ tcp_verify_left_out(tp);
+
+ /* Duplicate the behavior from Loss state (fastretrans_alert) */
+ if (flag & FLAG_DATA_ACKED)
+ inet_csk(sk)->icsk_retransmits = 0;
+
+ if ((flag & FLAG_NONHEAD_RETRANS_ACKED) ||
+ ((tp->frto_counter >= 2) && (flag & FLAG_RETRANS_DATA_ACKED)))
+ tp->undo_marker = 0;
+
+ if (!before(tp->snd_una, tp->frto_highmark)) {
+ tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 2 : 3), flag);
+ return 1;
+ }
+
+ if (!tcp_is_sackfrto(tp)) {
+ /* RFC4138 shortcoming in step 2; should also have case c):
+ * ACK isn't duplicate nor advances window, e.g., opposite dir
+ * data, winupdate
+ */
+ if (!(flag & FLAG_ANY_PROGRESS) && (flag & FLAG_NOT_DUP))
+ return 1;
+
+ if (!(flag & FLAG_DATA_ACKED)) {
+ tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 0 : 3),
+ flag);
+ return 1;
+ }
+ } else {
+ if (!(flag & FLAG_DATA_ACKED) && (tp->frto_counter == 1)) {
+ if (!tcp_packets_in_flight(tp)) {
+ tcp_enter_frto_loss(sk, 2, flag);
+ return true;
+ }
+
+ /* Prevent sending of new data. */
+ tp->snd_cwnd = min(tp->snd_cwnd,
+ tcp_packets_in_flight(tp));
+ return 1;
+ }
+
+ if ((tp->frto_counter >= 2) &&
+ (!(flag & FLAG_FORWARD_PROGRESS) ||
+ ((flag & FLAG_DATA_SACKED) &&
+ !(flag & FLAG_ONLY_ORIG_SACKED)))) {
+ /* RFC4138 shortcoming (see comment above) */
+ if (!(flag & FLAG_FORWARD_PROGRESS) &&
+ (flag & FLAG_NOT_DUP))
+ return 1;
+
+ tcp_enter_frto_loss(sk, 3, flag);
+ return 1;
+ }
+ }
+
+ if (tp->frto_counter == 1) {
+ /* tcp_may_send_now needs to see updated state */
+ tp->snd_cwnd = tcp_packets_in_flight(tp) + 2;
+ tp->frto_counter = 2;
+
+ if (!tcp_may_send_now(sk))
+ tcp_enter_frto_loss(sk, 2, flag);
+
+ return 1;
+ } else {
+ switch (sysctl_tcp_frto_response) {
+ case 2:
+ tcp_undo_spur_to_response(sk, flag);
+ break;
+ case 1:
+ tcp_conservative_spur_to_response(tp);
+ break;
+ default:
+ tcp_ratehalving_spur_to_response(sk);
+ break;
+ }
+ tp->frto_counter = 0;
+ tp->undo_marker = 0;
+ NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSPURIOUSRTOS);
+ }
+ return 0;
+}
+
+/* RFC 5961 7 [ACK Throttling] */
+static void tcp_send_challenge_ack(struct sock *sk)
+{
+ /* unprotected vars, we dont care of overwrites */
+ static u32 challenge_timestamp;
+ static unsigned int challenge_count;
+ u32 now = jiffies / HZ;
+
+ if (now != challenge_timestamp) {
+ challenge_timestamp = now;
+ challenge_count = 0;
+ }
+ if (++challenge_count <= sysctl_tcp_challenge_ack_limit) {
+ NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPCHALLENGEACK);
+ tcp_send_ack(sk);
+ }
+}
+
+static void tcp_store_ts_recent(struct tcp_sock *tp)
+{
+ tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
+ tp->rx_opt.ts_recent_stamp = get_seconds();
+}
+
+static void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
+{
+ if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
+ /* PAWS bug workaround wrt. ACK frames, the PAWS discard
+ * extra check below makes sure this can only happen
+ * for pure ACK frames. -DaveM
+ *
+ * Not only, also it occurs for expired timestamps.
+ */
+
+ if (tcp_paws_check(&tp->rx_opt, 0))
+ tcp_store_ts_recent(tp);
+ }
+}
+
+/* This routine deals with incoming acks, but not outgoing ones. */
+static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
+{
+ struct inet_connection_sock *icsk = inet_csk(sk);
+ struct tcp_sock *tp = tcp_sk(sk);
+ u32 prior_snd_una = tp->snd_una;
+ u32 ack_seq = TCP_SKB_CB(skb)->seq;
+ u32 ack = TCP_SKB_CB(skb)->ack_seq;
+ bool is_dupack = false;
+ u32 prior_in_flight;
+ u32 prior_fackets;
+ int prior_packets = tp->packets_out;
+ int prior_sacked = tp->sacked_out;
+ int pkts_acked = 0;
+ int previous_packets_out = 0;
+ int frto_cwnd = 0;
+
+ /* If the ack is older than previous acks
+ * then we can probably ignore it.
+ */
+ if (before(ack, prior_snd_una)) {
+ /* RFC 5961 5.2 [Blind Data Injection Attack].[Mitigation] */
+ if (before(ack, prior_snd_una - tp->max_window)) {
+ tcp_send_challenge_ack(sk);
+ return -1;
+ }
+ goto old_ack;
+ }
+
+ /* If the ack includes data we haven't sent yet, discard
+ * this segment (RFC793 Section 3.9).
+ */
+ if (after(ack, tp->snd_nxt))
+ goto invalid_ack;
+
+ if (after(ack, prior_snd_una))
+ flag |= FLAG_SND_UNA_ADVANCED;
+
+ if (sysctl_tcp_abc) {
+ if (icsk->icsk_ca_state < TCP_CA_CWR)
+ tp->bytes_acked += ack - prior_snd_una;
+ else if (icsk->icsk_ca_state == TCP_CA_Loss)
+ /* we assume just one segment left network */
+ tp->bytes_acked += min(ack - prior_snd_una,
+ tp->mss_cache);
+ }
+
+ prior_fackets = tp->fackets_out;
+ prior_in_flight = tcp_packets_in_flight(tp);
+
+ /* ts_recent update must be made after we are sure that the packet
+ * is in window.
+ */
+ if (flag & FLAG_UPDATE_TS_RECENT)
+ tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
+
+ if (!(flag & FLAG_SLOWPATH) && after(ack, prior_snd_una)) {
+ /* Window is constant, pure forward advance.
+ * No more checks are required.
+ * Note, we use the fact that SND.UNA>=SND.WL2.
+ */
+ tcp_update_wl(tp, ack_seq);
+ tp->snd_una = ack;
+ flag |= FLAG_WIN_UPDATE;
+
+ tcp_ca_event(sk, CA_EVENT_FAST_ACK);
+
+ NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPACKS);
+ } else {
+ if (ack_seq != TCP_SKB_CB(skb)->end_seq)
+ flag |= FLAG_DATA;
+ else
+ NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPPUREACKS);
+
+ flag |= tcp_ack_update_window(sk, skb, ack, ack_seq);
+
+ if (TCP_SKB_CB(skb)->sacked)
+ flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una);
+
+ if (TCP_ECN_rcv_ecn_echo(tp, tcp_hdr(skb)))
+ flag |= FLAG_ECE;
+
+ tcp_ca_event(sk, CA_EVENT_SLOW_ACK);
+ }
+
+ /* We passed data and got it acked, remove any soft error
+ * log. Something worked...
+ */
+ sk->sk_err_soft = 0;
+ icsk->icsk_probes_out = 0;
+ tp->rcv_tstamp = tcp_time_stamp;
+ if (!prior_packets)
+ goto no_queue;
+
+ /* See if we can take anything off of the retransmit queue. */
+ previous_packets_out = tp->packets_out;
+ flag |= tcp_clean_rtx_queue(sk, prior_fackets, prior_snd_una);
+
+ pkts_acked = previous_packets_out - tp->packets_out;
+
+ if (tp->frto_counter)
+ frto_cwnd = tcp_process_frto(sk, flag);
+ /* Guarantee sacktag reordering detection against wrap-arounds */
+ if (before(tp->frto_highmark, tp->snd_una))
+ tp->frto_highmark = 0;
+
+ if (tcp_ack_is_dubious(sk, flag)) {
+ /* Advance CWND, if state allows this. */
+ if ((flag & FLAG_DATA_ACKED) && !frto_cwnd &&
+ tcp_may_raise_cwnd(sk, flag))
+ tcp_cong_avoid(sk, ack, prior_in_flight);
+ is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP));
+ tcp_fastretrans_alert(sk, pkts_acked, prior_sacked,
+ prior_packets, is_dupack, flag);
+ } else {
+ if ((flag & FLAG_DATA_ACKED) && !frto_cwnd)
+ tcp_cong_avoid(sk, ack, prior_in_flight);
+ }
+
+ if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP))
+ dst_confirm(__sk_dst_get(sk));
+
+ return 1;
+
+no_queue:
+ /* If data was DSACKed, see if we can undo a cwnd reduction. */
+ if (flag & FLAG_DSACKING_ACK)
+ tcp_fastretrans_alert(sk, pkts_acked, prior_sacked,
+ prior_packets, is_dupack, flag);
+ /* If this ack opens up a zero window, clear backoff. It was
+ * being used to time the probes, and is probably far higher than
+ * it needs to be for normal retransmission.
+ */
+ if (tcp_send_head(sk))
+ tcp_ack_probe(sk);
+ return 1;
+
+invalid_ack:
+ SOCK_DEBUG(sk, "Ack %u after %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
+ return -1;
+
+old_ack:
+ /* If data was SACKed, tag it and see if we should send more data.
+ * If data was DSACKed, see if we can undo a cwnd reduction.
+ */
+ if (TCP_SKB_CB(skb)->sacked) {
+ flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una);
+ tcp_fastretrans_alert(sk, pkts_acked, prior_sacked,
+ prior_packets, is_dupack, flag);
+ }
+
+ SOCK_DEBUG(sk, "Ack %u before %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
+ return 0;
+}
+
+/* Look for tcp options. Normally only called on SYN and SYNACK packets.
+ * But, this can also be called on packets in the established flow when
+ * the fast version below fails.
+ */
+void tcp_parse_options(const struct sk_buff *skb, struct tcp_options_received *opt_rx,
+ const u8 **hvpp, int estab)
+{
+ const unsigned char *ptr;
+ const struct tcphdr *th = tcp_hdr(skb);
+ int length = (th->doff * 4) - sizeof(struct tcphdr);
+
+ ptr = (const unsigned char *)(th + 1);
+ opt_rx->saw_tstamp = 0;
+
+ while (length > 0) {
+ int opcode = *ptr++;
+ int opsize;
+
+ switch (opcode) {
+ case TCPOPT_EOL:
+ return;
+ case TCPOPT_NOP: /* Ref: RFC 793 section 3.1 */
+ length--;
+ continue;
+ default:
+ opsize = *ptr++;
+ if (opsize < 2) /* "silly options" */
+ return;
+ if (opsize > length)
+ return; /* don't parse partial options */
+ switch (opcode) {
+ case TCPOPT_MSS:
+ if (opsize == TCPOLEN_MSS && th->syn && !estab) {
+ u16 in_mss = get_unaligned_be16(ptr);
+ if (in_mss) {
+ if (opt_rx->user_mss &&
+ opt_rx->user_mss < in_mss)
+ in_mss = opt_rx->user_mss;
+ opt_rx->mss_clamp = in_mss;
+ }
+ }
+ break;
+ case TCPOPT_WINDOW:
+ if (opsize == TCPOLEN_WINDOW && th->syn &&
+ !estab && sysctl_tcp_window_scaling) {
+ __u8 snd_wscale = *(__u8 *)ptr;
+ opt_rx->wscale_ok = 1;
+ if (snd_wscale > 14) {
+ if (net_ratelimit())
+ pr_info("%s: Illegal window scaling value %d >14 received\n",
+ __func__,
+ snd_wscale);
+ snd_wscale = 14;
+ }
+ opt_rx->snd_wscale = snd_wscale;
+ }
+ break;
+ case TCPOPT_TIMESTAMP:
+ if ((opsize == TCPOLEN_TIMESTAMP) &&
+ ((estab && opt_rx->tstamp_ok) ||
+ (!estab && sysctl_tcp_timestamps))) {
+ opt_rx->saw_tstamp = 1;
+ opt_rx->rcv_tsval = get_unaligned_be32(ptr);
+ opt_rx->rcv_tsecr = get_unaligned_be32(ptr + 4);
+ }
+ break;
+ case TCPOPT_SACK_PERM:
+ if (opsize == TCPOLEN_SACK_PERM && th->syn &&
+ !estab && sysctl_tcp_sack) {
+ opt_rx->sack_ok = TCP_SACK_SEEN;
+ tcp_sack_reset(opt_rx);
+ }
+ break;
+
+ case TCPOPT_SACK:
+ if ((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
+ !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
+ opt_rx->sack_ok) {
+ TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
+ }
+ break;
+#ifdef CONFIG_TCP_MD5SIG
+ case TCPOPT_MD5SIG:
+ /*
+ * The MD5 Hash has already been
+ * checked (see tcp_v{4,6}_do_rcv()).
+ */
+ break;
+#endif
+ case TCPOPT_COOKIE:
+ /* This option is variable length.
+ */
+ switch (opsize) {
+ case TCPOLEN_COOKIE_BASE:
+ /* not yet implemented */
+ break;
+ case TCPOLEN_COOKIE_PAIR:
+ /* not yet implemented */
+ break;
+ case TCPOLEN_COOKIE_MIN+0:
+ case TCPOLEN_COOKIE_MIN+2:
+ case TCPOLEN_COOKIE_MIN+4:
+ case TCPOLEN_COOKIE_MIN+6:
+ case TCPOLEN_COOKIE_MAX:
+ /* 16-bit multiple */
+ opt_rx->cookie_plus = opsize;
+ *hvpp = ptr;
+ break;
+ default:
+ /* ignore option */
+ break;
+ }
+ break;
+ }
+
+ ptr += opsize-2;
+ length -= opsize;
+ }
+ }
+}
+EXPORT_SYMBOL(tcp_parse_options);
+
+static int tcp_parse_aligned_timestamp(struct tcp_sock *tp, const struct tcphdr *th)
+{
+ const __be32 *ptr = (const __be32 *)(th + 1);
+
+ if (*ptr == htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
+ | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
+ tp->rx_opt.saw_tstamp = 1;
+ ++ptr;
+ tp->rx_opt.rcv_tsval = ntohl(*ptr);
+ ++ptr;
+ tp->rx_opt.rcv_tsecr = ntohl(*ptr);
+ return 1;
+ }
+ return 0;
+}
+
+/* Fast parse options. This hopes to only see timestamps.
+ * If it is wrong it falls back on tcp_parse_options().
+ */
+static int tcp_fast_parse_options(const struct sk_buff *skb,
+ const struct tcphdr *th,
+ struct tcp_sock *tp, const u8 **hvpp)
+{
+ /* In the spirit of fast parsing, compare doff directly to constant
+ * values. Because equality is used, short doff can be ignored here.
+ */
+ if (th->doff == (sizeof(*th) / 4)) {
+ tp->rx_opt.saw_tstamp = 0;
+ return 0;
+ } else if (tp->rx_opt.tstamp_ok &&
+ th->doff == ((sizeof(*th) + TCPOLEN_TSTAMP_ALIGNED) / 4)) {
+ if (tcp_parse_aligned_timestamp(tp, th))
+ return 1;
+ }
+ tcp_parse_options(skb, &tp->rx_opt, hvpp, 1);
+ return 1;
+}
+
+#ifdef CONFIG_TCP_MD5SIG
+/*
+ * Parse MD5 Signature option
+ */
+const u8 *tcp_parse_md5sig_option(const struct tcphdr *th)
+{
+ int length = (th->doff << 2) - sizeof(*th);
+ const u8 *ptr = (const u8 *)(th + 1);
+
+ /* If the TCP option is too short, we can short cut */
+ if (length < TCPOLEN_MD5SIG)
+ return NULL;
+
+ while (length > 0) {
+ int opcode = *ptr++;
+ int opsize;
+
+ switch(opcode) {
+ case TCPOPT_EOL:
+ return NULL;
+ case TCPOPT_NOP:
+ length--;
+ continue;
+ default:
+ opsize = *ptr++;
+ if (opsize < 2 || opsize > length)
+ return NULL;
+ if (opcode == TCPOPT_MD5SIG)
+ return opsize == TCPOLEN_MD5SIG ? ptr : NULL;
+ }
+ ptr += opsize - 2;
+ length -= opsize;
+ }
+ return NULL;
+}
+EXPORT_SYMBOL(tcp_parse_md5sig_option);
+#endif
+
+/* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
+ *
+ * It is not fatal. If this ACK does _not_ change critical state (seqs, window)
+ * it can pass through stack. So, the following predicate verifies that
+ * this segment is not used for anything but congestion avoidance or
+ * fast retransmit. Moreover, we even are able to eliminate most of such
+ * second order effects, if we apply some small "replay" window (~RTO)
+ * to timestamp space.
+ *
+ * All these measures still do not guarantee that we reject wrapped ACKs
+ * on networks with high bandwidth, when sequence space is recycled fastly,
+ * but it guarantees that such events will be very rare and do not affect
+ * connection seriously. This doesn't look nice, but alas, PAWS is really
+ * buggy extension.
+ *
+ * [ Later note. Even worse! It is buggy for segments _with_ data. RFC
+ * states that events when retransmit arrives after original data are rare.
+ * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
+ * the biggest problem on large power networks even with minor reordering.
+ * OK, let's give it small replay window. If peer clock is even 1hz, it is safe
+ * up to bandwidth of 18Gigabit/sec. 8) ]
+ */
+
+static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
+{
+ const struct tcp_sock *tp = tcp_sk(sk);
+ const struct tcphdr *th = tcp_hdr(skb);
+ u32 seq = TCP_SKB_CB(skb)->seq;
+ u32 ack = TCP_SKB_CB(skb)->ack_seq;
+
+ return (/* 1. Pure ACK with correct sequence number. */
+ (th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&
+
+ /* 2. ... and duplicate ACK. */
+ ack == tp->snd_una &&
+
+ /* 3. ... and does not update window. */
+ !tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&
+
+ /* 4. ... and sits in replay window. */
+ (s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
+}
+
+static inline int tcp_paws_discard(const struct sock *sk,
+ const struct sk_buff *skb)
+{
+ const struct tcp_sock *tp = tcp_sk(sk);
+
+ return !tcp_paws_check(&tp->rx_opt, TCP_PAWS_WINDOW) &&
+ !tcp_disordered_ack(sk, skb);
+}
+
+/* Check segment sequence number for validity.
+ *
+ * Segment controls are considered valid, if the segment
+ * fits to the window after truncation to the window. Acceptability
+ * of data (and SYN, FIN, of course) is checked separately.
+ * See tcp_data_queue(), for example.
+ *
+ * Also, controls (RST is main one) are accepted using RCV.WUP instead
+ * of RCV.NXT. Peer still did not advance his SND.UNA when we
+ * delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
+ * (borrowed from freebsd)
+ */
+
+static inline int tcp_sequence(const struct tcp_sock *tp, u32 seq, u32 end_seq)
+{
+ return !before(end_seq, tp->rcv_wup) &&
+ !after(seq, tp->rcv_nxt + tcp_receive_window(tp));
+}
+
+/* When we get a reset we do this. */
+static void tcp_reset(struct sock *sk)
+{
+ TCP_PKT_STATS_INC(TCP_RST_RECV_NUM);
+ TCP_SOCK_TRACK(sk, TCP_RST_RECV);
+
+ /* We want the right error as BSD sees it (and indeed as we do). */
+ switch (sk->sk_state) {
+ case TCP_SYN_SENT:
+ sk->sk_err = ECONNREFUSED;
+ break;
+ case TCP_CLOSE_WAIT:
+ sk->sk_err = EPIPE;
+ break;
+ case TCP_CLOSE:
+ return;
+ default:
+ sk->sk_err = ECONNRESET;
+ ERRNO_TRACK(-ECONNRESET);
+ }
+ /* This barrier is coupled with smp_rmb() in tcp_poll() */
+ smp_wmb();
+
+ if (!sock_flag(sk, SOCK_DEAD))
+ sk->sk_error_report(sk);
+
+ tcp_done(sk);
+}
+
+/*
+ * Process the FIN bit. This now behaves as it is supposed to work
+ * and the FIN takes effect when it is validly part of sequence
+ * space. Not before when we get holes.
+ *
+ * If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
+ * (and thence onto LAST-ACK and finally, CLOSE, we never enter
+ * TIME-WAIT)
+ *
+ * If we are in FINWAIT-1, a received FIN indicates simultaneous
+ * close and we go into CLOSING (and later onto TIME-WAIT)
+ *
+ * If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
+ */
+static void tcp_fin(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ TCP_SOCK_TRACK(sk, TCP_FIN_RECV);
+
+ inet_csk_schedule_ack(sk);
+
+ sk->sk_shutdown |= RCV_SHUTDOWN;
+ sock_set_flag(sk, SOCK_DONE);
+
+ switch (sk->sk_state) {
+ case TCP_SYN_RECV:
+ case TCP_ESTABLISHED:
+ /* Move to CLOSE_WAIT */
+ tcp_set_state(sk, TCP_CLOSE_WAIT);
+ inet_csk(sk)->icsk_ack.pingpong = 1;
+ break;
+
+ case TCP_CLOSE_WAIT:
+ case TCP_CLOSING:
+ /* Received a retransmission of the FIN, do
+ * nothing.
+ */
+ break;
+ case TCP_LAST_ACK:
+ /* RFC793: Remain in the LAST-ACK state. */
+ break;
+
+ case TCP_FIN_WAIT1:
+ /* This case occurs when a simultaneous close
+ * happens, we must ack the received FIN and
+ * enter the CLOSING state.
+ */
+ tcp_send_ack(sk);
+ tcp_set_state(sk, TCP_CLOSING);
+ break;
+ case TCP_FIN_WAIT2:
+ /* Received a FIN -- send ACK and enter TIME_WAIT. */
+ tcp_send_ack(sk);
+ tcp_time_wait(sk, TCP_TIME_WAIT, 0);
+ break;
+ default:
+ /* Only TCP_LISTEN and TCP_CLOSE are left, in these
+ * cases we should never reach this piece of code.
+ */
+ pr_err("%s: Impossible, sk->sk_state=%d\n",
+ __func__, sk->sk_state);
+ break;
+ }
+
+ /* It _is_ possible, that we have something out-of-order _after_ FIN.
+ * Probably, we should reset in this case. For now drop them.
+ */
+ __skb_queue_purge(&tp->out_of_order_queue);
+ if (tcp_is_sack(tp))
+ tcp_sack_reset(&tp->rx_opt);
+ sk_mem_reclaim(sk);
+
+ if (!sock_flag(sk, SOCK_DEAD)) {
+ sk->sk_state_change(sk);
+
+ /* Do not send POLL_HUP for half duplex close. */
+ if (sk->sk_shutdown == SHUTDOWN_MASK ||
+ sk->sk_state == TCP_CLOSE)
+ sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP);
+ else
+ sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN);
+ }
+}
+
+static inline int tcp_sack_extend(struct tcp_sack_block *sp, u32 seq,
+ u32 end_seq)
+{
+ if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
+ if (before(seq, sp->start_seq))
+ sp->start_seq = seq;
+ if (after(end_seq, sp->end_seq))
+ sp->end_seq = end_seq;
+ return 1;
+ }
+ return 0;
+}
+
+static void tcp_dsack_set(struct sock *sk, u32 seq, u32 end_seq)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
+ int mib_idx;
+
+ if (before(seq, tp->rcv_nxt))
+ mib_idx = LINUX_MIB_TCPDSACKOLDSENT;
+ else
+ mib_idx = LINUX_MIB_TCPDSACKOFOSENT;
+
+ NET_INC_STATS_BH(sock_net(sk), mib_idx);
+
+ tp->rx_opt.dsack = 1;
+ tp->duplicate_sack[0].start_seq = seq;
+ tp->duplicate_sack[0].end_seq = end_seq;
+ }
+}
+
+static void tcp_dsack_extend(struct sock *sk, u32 seq, u32 end_seq)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ if (!tp->rx_opt.dsack)
+ tcp_dsack_set(sk, seq, end_seq);
+ else
+ tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
+}
+
+static void tcp_send_dupack(struct sock *sk, const struct sk_buff *skb)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
+ before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
+ NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
+ tcp_enter_quickack_mode(sk);
+
+ if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
+ u32 end_seq = TCP_SKB_CB(skb)->end_seq;
+
+ if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
+ end_seq = tp->rcv_nxt;
+ tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, end_seq);
+ }
+ }
+
+ tcp_send_ack(sk);
+}
+
+/* These routines update the SACK block as out-of-order packets arrive or
+ * in-order packets close up the sequence space.
+ */
+static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
+{
+ int this_sack;
+ struct tcp_sack_block *sp = &tp->selective_acks[0];
+ struct tcp_sack_block *swalk = sp + 1;
+
+ /* See if the recent change to the first SACK eats into
+ * or hits the sequence space of other SACK blocks, if so coalesce.
+ */
+ for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;) {
+ if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
+ int i;
+
+ /* Zap SWALK, by moving every further SACK up by one slot.
+ * Decrease num_sacks.
+ */
+ tp->rx_opt.num_sacks--;
+ for (i = this_sack; i < tp->rx_opt.num_sacks; i++)
+ sp[i] = sp[i + 1];
+ continue;
+ }
+ this_sack++, swalk++;
+ }
+}
+
+static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct tcp_sack_block *sp = &tp->selective_acks[0];
+ int cur_sacks = tp->rx_opt.num_sacks;
+ int this_sack;
+
+ if (!cur_sacks)
+ goto new_sack;
+
+ for (this_sack = 0; this_sack < cur_sacks; this_sack++, sp++) {
+ if (tcp_sack_extend(sp, seq, end_seq)) {
+ /* Rotate this_sack to the first one. */
+ for (; this_sack > 0; this_sack--, sp--)
+ swap(*sp, *(sp - 1));
+ if (cur_sacks > 1)
+ tcp_sack_maybe_coalesce(tp);
+ return;
+ }
+ }
+
+ /* Could not find an adjacent existing SACK, build a new one,
+ * put it at the front, and shift everyone else down. We
+ * always know there is at least one SACK present already here.
+ *
+ * If the sack array is full, forget about the last one.
+ */
+ if (this_sack >= TCP_NUM_SACKS) {
+ this_sack--;
+ tp->rx_opt.num_sacks--;
+ sp--;
+ }
+ for (; this_sack > 0; this_sack--, sp--)
+ *sp = *(sp - 1);
+
+new_sack:
+ /* Build the new head SACK, and we're done. */
+ sp->start_seq = seq;
+ sp->end_seq = end_seq;
+ tp->rx_opt.num_sacks++;
+}
+
+/* RCV.NXT advances, some SACKs should be eaten. */
+
+static void tcp_sack_remove(struct tcp_sock *tp)
+{
+ struct tcp_sack_block *sp = &tp->selective_acks[0];
+ int num_sacks = tp->rx_opt.num_sacks;
+ int this_sack;
+
+ /* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
+ if (skb_queue_empty(&tp->out_of_order_queue)) {
+ tp->rx_opt.num_sacks = 0;
+ return;
+ }
+
+ for (this_sack = 0; this_sack < num_sacks;) {
+ /* Check if the start of the sack is covered by RCV.NXT. */
+ if (!before(tp->rcv_nxt, sp->start_seq)) {
+ int i;
+
+ /* RCV.NXT must cover all the block! */
+ WARN_ON(before(tp->rcv_nxt, sp->end_seq));
+
+ /* Zap this SACK, by moving forward any other SACKS. */
+ for (i=this_sack+1; i < num_sacks; i++)
+ tp->selective_acks[i-1] = tp->selective_acks[i];
+ num_sacks--;
+ continue;
+ }
+ this_sack++;
+ sp++;
+ }
+ tp->rx_opt.num_sacks = num_sacks;
+}
+
+/* This one checks to see if we can put data from the
+ * out_of_order queue into the receive_queue.
+ */
+static void tcp_ofo_queue(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ __u32 dsack_high = tp->rcv_nxt;
+ struct sk_buff *skb;
+
+ while ((skb = skb_peek(&tp->out_of_order_queue)) != NULL) {
+ if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
+ break;
+
+ if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
+ __u32 dsack = dsack_high;
+ if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
+ dsack_high = TCP_SKB_CB(skb)->end_seq;
+ tcp_dsack_extend(sk, TCP_SKB_CB(skb)->seq, dsack);
+ }
+
+ if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
+ SOCK_DEBUG(sk, "ofo packet was already received\n");
+ __skb_unlink(skb, &tp->out_of_order_queue);
+ __kfree_skb(skb);
+ continue;
+ }
+ SOCK_DEBUG(sk, "ofo requeuing : rcv_next %X seq %X - %X\n",
+ tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
+ TCP_SKB_CB(skb)->end_seq);
+
+ __skb_unlink(skb, &tp->out_of_order_queue);
+ __skb_queue_tail(&sk->sk_receive_queue, skb);
+ tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
+ if (tcp_hdr(skb)->fin)
+ tcp_fin(sk);
+ }
+}
+
+static int tcp_prune_ofo_queue(struct sock *sk);
+static int tcp_prune_queue(struct sock *sk);
+
+static inline int tcp_try_rmem_schedule(struct sock *sk, unsigned int size)
+{
+ if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
+ !sk_rmem_schedule(sk, size)) {
+
+ if (tcp_prune_queue(sk) < 0)
+ return -1;
+
+ if (!sk_rmem_schedule(sk, size)) {
+ if (!tcp_prune_ofo_queue(sk))
+ return -1;
+
+ if (!sk_rmem_schedule(sk, size))
+ return -1;
+ }
+ }
+ return 0;
+}
+
+static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct sk_buff *skb1;
+ u32 seq, end_seq;
+
+ TCP_ECN_check_ce(tp, skb);
+
+ if (tcp_try_rmem_schedule(sk, skb->truesize)) {
+ /* TODO: should increment a counter */
+ TCP_SOCK_TRACK(sk, TCP_RECV_BUFF_FULL);
+ __kfree_skb(skb);
+ return;
+ }
+
+ /* Disable header prediction. */
+ tp->pred_flags = 0;
+ inet_csk_schedule_ack(sk);
+
+ SOCK_DEBUG(sk, "out of order segment: rcv_next %X seq %X - %X\n",
+ tp->rcv_nxt, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
+
+ skb1 = skb_peek_tail(&tp->out_of_order_queue);
+ if (!skb1) {
+ /* Initial out of order segment, build 1 SACK. */
+ if (tcp_is_sack(tp)) {
+ tp->rx_opt.num_sacks = 1;
+ tp->selective_acks[0].start_seq = TCP_SKB_CB(skb)->seq;
+ tp->selective_acks[0].end_seq =
+ TCP_SKB_CB(skb)->end_seq;
+ }
+ __skb_queue_head(&tp->out_of_order_queue, skb);
+ goto end;
+ }
+
+ seq = TCP_SKB_CB(skb)->seq;
+ end_seq = TCP_SKB_CB(skb)->end_seq;
+
+ if (seq == TCP_SKB_CB(skb1)->end_seq) {
+ /* Packets in ofo can stay in queue a long time.
+ * Better try to coalesce them right now
+ * to avoid future tcp_collapse_ofo_queue(),
+ * probably the most expensive function in tcp stack.
+ */
+ if (skb->len <= skb_tailroom(skb1) && !tcp_hdr(skb)->fin) {
+ NET_INC_STATS_BH(sock_net(sk),
+ LINUX_MIB_TCPRCVCOALESCE);
+ BUG_ON(skb_copy_bits(skb, 0,
+ skb_put(skb1, skb->len),
+ skb->len));
+ TCP_SKB_CB(skb1)->end_seq = end_seq;
+ TCP_SKB_CB(skb1)->ack_seq = TCP_SKB_CB(skb)->ack_seq;
+ __kfree_skb(skb);
+ skb = NULL;
+ } else {
+ __skb_queue_after(&tp->out_of_order_queue, skb1, skb);
+ }
+
+ if (!tp->rx_opt.num_sacks ||
+ tp->selective_acks[0].end_seq != seq)
+ goto add_sack;
+
+ /* Common case: data arrive in order after hole. */
+ tp->selective_acks[0].end_seq = end_seq;
+ goto end;
+ }
+
+ /* Find place to insert this segment. */
+ while (1) {
+ if (!after(TCP_SKB_CB(skb1)->seq, seq))
+ break;
+ if (skb_queue_is_first(&tp->out_of_order_queue, skb1)) {
+ skb1 = NULL;
+ break;
+ }
+ skb1 = skb_queue_prev(&tp->out_of_order_queue, skb1);
+ }
+
+ /* Do skb overlap to previous one? */
+ if (skb1 && before(seq, TCP_SKB_CB(skb1)->end_seq)) {
+ if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
+ /* All the bits are present. Drop. */
+ __kfree_skb(skb);
+ skb = NULL;
+ tcp_dsack_set(sk, seq, end_seq);
+ goto add_sack;
+ }
+ if (after(seq, TCP_SKB_CB(skb1)->seq)) {
+ /* Partial overlap. */
+ tcp_dsack_set(sk, seq,
+ TCP_SKB_CB(skb1)->end_seq);
+ } else {
+ if (skb_queue_is_first(&tp->out_of_order_queue,
+ skb1))
+ skb1 = NULL;
+ else
+ skb1 = skb_queue_prev(
+ &tp->out_of_order_queue,
+ skb1);
+ }
+ }
+ if (!skb1)
+ __skb_queue_head(&tp->out_of_order_queue, skb);
+ else
+ __skb_queue_after(&tp->out_of_order_queue, skb1, skb);
+
+ /* And clean segments covered by new one as whole. */
+ while (!skb_queue_is_last(&tp->out_of_order_queue, skb)) {
+ skb1 = skb_queue_next(&tp->out_of_order_queue, skb);
+
+ if (!after(end_seq, TCP_SKB_CB(skb1)->seq))
+ break;
+ if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
+ tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
+ end_seq);
+ break;
+ }
+ __skb_unlink(skb1, &tp->out_of_order_queue);
+ tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
+ TCP_SKB_CB(skb1)->end_seq);
+ __kfree_skb(skb1);
+ }
+
+add_sack:
+ if (tcp_is_sack(tp))
+ tcp_sack_new_ofo_skb(sk, seq, end_seq);
+end:
+ if (skb)
+ skb_set_owner_r(skb, sk);
+}
+
+
+static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
+{
+ const struct tcphdr *th = tcp_hdr(skb);
+ struct tcp_sock *tp = tcp_sk(sk);
+ int eaten = -1;
+
+ if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq)
+ goto drop;
+
+ skb_dst_drop(skb);
+ __skb_pull(skb, th->doff * 4);
+
+ TCP_ECN_accept_cwr(tp, skb);
+
+ tp->rx_opt.dsack = 0;
+
+ /* Queue data for delivery to the user.
+ * Packets in sequence go to the receive queue.
+ * Out of sequence packets to the out_of_order_queue.
+ */
+ if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
+ if (tcp_receive_window(tp) == 0)
+ goto out_of_window;
+
+ /* Ok. In sequence. In window. */
+ if (tp->ucopy.task == current &&
+ tp->copied_seq == tp->rcv_nxt && tp->ucopy.len &&
+ sock_owned_by_user(sk) && !tp->urg_data) {
+ int chunk = min_t(unsigned int, skb->len,
+ tp->ucopy.len);
+
+ __set_current_state(TASK_RUNNING);
+
+ local_bh_enable();
+ if (!skb_copy_datagram_iovec(skb, 0, tp->ucopy.iov, chunk)) {
+ tp->ucopy.len -= chunk;
+ tp->copied_seq += chunk;
+ eaten = (chunk == skb->len);
+ tcp_rcv_space_adjust(sk);
+ }
+ local_bh_disable();
+ }
+
+ if (eaten <= 0) {
+queue_and_out:
+ if (eaten < 0 &&
+ tcp_try_rmem_schedule(sk, skb->truesize))
+ {
+ TCP_SOCK_TRACK(sk, TCP_RECV_BUFF_FULL);
+ goto drop;
+ }
+
+ skb_set_owner_r(skb, sk);
+ __skb_queue_tail(&sk->sk_receive_queue, skb);
+ }
+ tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
+ if (skb->len)
+ tcp_event_data_recv(sk, skb);
+ if (th->fin)
+ tcp_fin(sk);
+
+ if (!skb_queue_empty(&tp->out_of_order_queue)) {
+
+ /*ÔÚ¿ìËÙÖØ´«Ê±£¬µ±Á¬ÐøÊÕµ½3¸öÒ»ÑùµÄACKʱ£¬ÖØ´«±¨ÎÄ£¬ËùÒÔ¿ÉÒÔÈÏΪÂÒÐò´ïµ½3¸ö£¬³öÏÖ¶ª°ü*/
+ if(tp->out_of_order_queue.qlen >= 3)
+ TCP_PKT_STATS_INC(TCP_RECV_DROPS);
+
+ tcp_ofo_queue(sk);
+
+ /* RFC2581. 4.2. SHOULD send immediate ACK, when
+ * gap in queue is filled.
+ */
+ if (skb_queue_empty(&tp->out_of_order_queue))
+ inet_csk(sk)->icsk_ack.pingpong = 0;
+ }
+
+ if (tp->rx_opt.num_sacks)
+ tcp_sack_remove(tp);
+
+ tcp_fast_path_check(sk);
+
+ if (eaten > 0)
+ __kfree_skb(skb);
+ else if (!sock_flag(sk, SOCK_DEAD))
+ sk->sk_data_ready(sk, 0);
+ return;
+ }
+
+ if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
+ /* A retransmit, 2nd most common case. Force an immediate ack. */
+ NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
+ tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
+
+ /*´Ëʱ½ÓÊն˻صĵÄACK°ü¶ªÊ§*/
+ TCP_PKT_STATS_INC(TCP_SEND_DROPS);
+
+out_of_window:
+ TCP_SOCK_TRACK(sk, TCP_RECV_WINDOW_FULL);
+ tcp_enter_quickack_mode(sk);
+ inet_csk_schedule_ack(sk);
+drop:
+ __kfree_skb(skb);
+ return;
+ }
+
+ /* Out of window. F.e. zero window probe. */
+ if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt + tcp_receive_window(tp)))
+ goto out_of_window;
+
+ tcp_enter_quickack_mode(sk);
+
+ if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
+ /* Partial packet, seq < rcv_next < end_seq */
+ SOCK_DEBUG(sk, "partial packet: rcv_next %X seq %X - %X\n",
+ tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
+ TCP_SKB_CB(skb)->end_seq);
+
+ tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);
+
+ /* If window is closed, drop tail of packet. But after
+ * remembering D-SACK for its head made in previous line.
+ */
+ if (!tcp_receive_window(tp))
+ goto out_of_window;
+ goto queue_and_out;
+ }
+
+ tcp_data_queue_ofo(sk, skb);
+}
+
+static struct sk_buff *tcp_collapse_one(struct sock *sk, struct sk_buff *skb,
+ struct sk_buff_head *list)
+{
+ struct sk_buff *next = NULL;
+
+ if (!skb_queue_is_last(list, skb))
+ next = skb_queue_next(list, skb);
+
+ __skb_unlink(skb, list);
+ __kfree_skb(skb);
+ NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRCVCOLLAPSED);
+
+ return next;
+}
+
+/* Collapse contiguous sequence of skbs head..tail with
+ * sequence numbers start..end.
+ *
+ * If tail is NULL, this means until the end of the list.
+ *
+ * Segments with FIN/SYN are not collapsed (only because this
+ * simplifies code)
+ */
+static void
+tcp_collapse(struct sock *sk, struct sk_buff_head *list,
+ struct sk_buff *head, struct sk_buff *tail,
+ u32 start, u32 end)
+{
+ struct sk_buff *skb, *n;
+ bool end_of_skbs;
+
+ /* First, check that queue is collapsible and find
+ * the point where collapsing can be useful. */
+ skb = head;
+restart:
+ end_of_skbs = true;
+ skb_queue_walk_from_safe(list, skb, n) {
+ if (skb == tail)
+ break;
+ /* No new bits? It is possible on ofo queue. */
+ if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
+ skb = tcp_collapse_one(sk, skb, list);
+ if (!skb)
+ break;
+ goto restart;
+ }
+
+ /* The first skb to collapse is:
+ * - not SYN/FIN and
+ * - bloated or contains data before "start" or
+ * overlaps to the next one.
+ */
+ if (!tcp_hdr(skb)->syn && !tcp_hdr(skb)->fin &&
+ (tcp_win_from_space(skb->truesize) > skb->len ||
+ before(TCP_SKB_CB(skb)->seq, start))) {
+ end_of_skbs = false;
+ break;
+ }
+
+ if (!skb_queue_is_last(list, skb)) {
+ struct sk_buff *next = skb_queue_next(list, skb);
+ if (next != tail &&
+ TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(next)->seq) {
+ end_of_skbs = false;
+ break;
+ }
+ }
+
+ /* Decided to skip this, advance start seq. */
+ start = TCP_SKB_CB(skb)->end_seq;
+ }
+ if (end_of_skbs || tcp_hdr(skb)->syn || tcp_hdr(skb)->fin)
+ return;
+
+ while (before(start, end)) {
+ struct sk_buff *nskb;
+ unsigned int header = skb_headroom(skb);
+ int copy = SKB_MAX_ORDER(header, 0);
+
+ /* Too big header? This can happen with IPv6. */
+ if (copy < 0)
+ return;
+ if (end - start < copy)
+ copy = end - start;
+ nskb = alloc_skb(copy + header, GFP_ATOMIC);
+ if (!nskb)
+ return;
+
+ skb_set_mac_header(nskb, skb_mac_header(skb) - skb->head);
+ skb_set_network_header(nskb, (skb_network_header(skb) -
+ skb->head));
+ skb_set_transport_header(nskb, (skb_transport_header(skb) -
+ skb->head));
+ skb_reserve(nskb, header);
+ memcpy(nskb->head, skb->head, header);
+ memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
+ TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
+ __skb_queue_before(list, skb, nskb);
+ skb_set_owner_r(nskb, sk);
+
+ /* Copy data, releasing collapsed skbs. */
+ while (copy > 0) {
+ int offset = start - TCP_SKB_CB(skb)->seq;
+ int size = TCP_SKB_CB(skb)->end_seq - start;
+
+ BUG_ON(offset < 0);
+ if (size > 0) {
+ size = min(copy, size);
+ if (skb_copy_bits(skb, offset, skb_put(nskb, size), size))
+ BUG();
+ TCP_SKB_CB(nskb)->end_seq += size;
+ copy -= size;
+ start += size;
+ }
+ if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
+ skb = tcp_collapse_one(sk, skb, list);
+ if (!skb ||
+ skb == tail ||
+ tcp_hdr(skb)->syn ||
+ tcp_hdr(skb)->fin)
+ return;
+ }
+ }
+ }
+}
+
+/* Collapse ofo queue. Algorithm: select contiguous sequence of skbs
+ * and tcp_collapse() them until all the queue is collapsed.
+ */
+static void tcp_collapse_ofo_queue(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct sk_buff *skb = skb_peek(&tp->out_of_order_queue);
+ struct sk_buff *head;
+ u32 start, end;
+
+ if (skb == NULL)
+ return;
+
+ start = TCP_SKB_CB(skb)->seq;
+ end = TCP_SKB_CB(skb)->end_seq;
+ head = skb;
+
+ for (;;) {
+ struct sk_buff *next = NULL;
+
+ if (!skb_queue_is_last(&tp->out_of_order_queue, skb))
+ next = skb_queue_next(&tp->out_of_order_queue, skb);
+ skb = next;
+
+ /* Segment is terminated when we see gap or when
+ * we are at the end of all the queue. */
+ if (!skb ||
+ after(TCP_SKB_CB(skb)->seq, end) ||
+ before(TCP_SKB_CB(skb)->end_seq, start)) {
+ tcp_collapse(sk, &tp->out_of_order_queue,
+ head, skb, start, end);
+ head = skb;
+ if (!skb)
+ break;
+ /* Start new segment */
+ start = TCP_SKB_CB(skb)->seq;
+ end = TCP_SKB_CB(skb)->end_seq;
+ } else {
+ if (before(TCP_SKB_CB(skb)->seq, start))
+ start = TCP_SKB_CB(skb)->seq;
+ if (after(TCP_SKB_CB(skb)->end_seq, end))
+ end = TCP_SKB_CB(skb)->end_seq;
+ }
+ }
+}
+
+/*
+ * Purge the out-of-order queue.
+ * Return true if queue was pruned.
+ */
+static int tcp_prune_ofo_queue(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ int res = 0;
+
+ if (!skb_queue_empty(&tp->out_of_order_queue)) {
+ NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_OFOPRUNED);
+ __skb_queue_purge(&tp->out_of_order_queue);
+
+ /* Reset SACK state. A conforming SACK implementation will
+ * do the same at a timeout based retransmit. When a connection
+ * is in a sad state like this, we care only about integrity
+ * of the connection not performance.
+ */
+ if (tp->rx_opt.sack_ok)
+ tcp_sack_reset(&tp->rx_opt);
+ sk_mem_reclaim(sk);
+ res = 1;
+ }
+ return res;
+}
+
+/* Reduce allocated memory if we can, trying to get
+ * the socket within its memory limits again.
+ *
+ * Return less than zero if we should start dropping frames
+ * until the socket owning process reads some of the data
+ * to stabilize the situation.
+ */
+static int tcp_prune_queue(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ SOCK_DEBUG(sk, "prune_queue: c=%x\n", tp->copied_seq);
+
+ NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PRUNECALLED);
+
+ if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
+ tcp_clamp_window(sk);
+ else if (sk_under_memory_pressure(sk))
+ tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss);
+
+ tcp_collapse_ofo_queue(sk);
+ if (!skb_queue_empty(&sk->sk_receive_queue))
+ tcp_collapse(sk, &sk->sk_receive_queue,
+ skb_peek(&sk->sk_receive_queue),
+ NULL,
+ tp->copied_seq, tp->rcv_nxt);
+ sk_mem_reclaim(sk);
+
+ if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
+ return 0;
+
+ /* Collapsing did not help, destructive actions follow.
+ * This must not ever occur. */
+
+ tcp_prune_ofo_queue(sk);
+
+ if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
+ return 0;
+
+ /* If we are really being abused, tell the caller to silently
+ * drop receive data on the floor. It will get retransmitted
+ * and hopefully then we'll have sufficient space.
+ */
+ NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_RCVPRUNED);
+
+ /* Massive buffer overcommit. */
+ tp->pred_flags = 0;
+ return -1;
+}
+
+/* RFC2861, slow part. Adjust cwnd, after it was not full during one rto.
+ * As additional protections, we do not touch cwnd in retransmission phases,
+ * and if application hit its sndbuf limit recently.
+ */
+void tcp_cwnd_application_limited(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
+ sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
+ /* Limited by application or receiver window. */
+ u32 init_win = tcp_init_cwnd(tp, __sk_dst_get(sk));
+ u32 win_used = max(tp->snd_cwnd_used, init_win);
+ if (win_used < tp->snd_cwnd) {
+ tp->snd_ssthresh = tcp_current_ssthresh(sk);
+ tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;
+ }
+ tp->snd_cwnd_used = 0;
+ }
+ tp->snd_cwnd_stamp = tcp_time_stamp;
+}
+
+static int tcp_should_expand_sndbuf(const struct sock *sk)
+{
+ const struct tcp_sock *tp = tcp_sk(sk);
+
+ /* If the user specified a specific send buffer setting, do
+ * not modify it.
+ */
+ if (sk->sk_userlocks & SOCK_SNDBUF_LOCK)
+ return 0;
+
+ /* If we are under global TCP memory pressure, do not expand. */
+ if (sk_under_memory_pressure(sk))
+ return 0;
+
+ /* If we are under soft global TCP memory pressure, do not expand. */
+ if (sk_memory_allocated(sk) >= sk_prot_mem_limits(sk, 0))
+ return 0;
+
+ /* If we filled the congestion window, do not expand. */
+ if (tp->packets_out >= tp->snd_cwnd)
+ return 0;
+
+ return 1;
+}
+
+/* When incoming ACK allowed to free some skb from write_queue,
+ * we remember this event in flag SOCK_QUEUE_SHRUNK and wake up socket
+ * on the exit from tcp input handler.
+ *
+ * PROBLEM: sndbuf expansion does not work well with largesend.
+ */
+static void tcp_new_space(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ if (tcp_should_expand_sndbuf(sk)) {
+ int sndmem = SKB_TRUESIZE(max_t(u32,
+ tp->rx_opt.mss_clamp,
+ tp->mss_cache) +
+ MAX_TCP_HEADER);
+ int demanded = max_t(unsigned int, tp->snd_cwnd,
+ tp->reordering + 1);
+ sndmem *= 2 * demanded;
+ if (sndmem > sk->sk_sndbuf)
+ sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]);
+ tp->snd_cwnd_stamp = tcp_time_stamp;
+ }
+
+ sk->sk_write_space(sk);
+}
+
+static void tcp_check_space(struct sock *sk)
+{
+ if (sock_flag(sk, SOCK_QUEUE_SHRUNK)) {
+ sock_reset_flag(sk, SOCK_QUEUE_SHRUNK);
+ if (sk->sk_socket &&
+ test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
+ tcp_new_space(sk);
+ }
+}
+
+static inline void tcp_data_snd_check(struct sock *sk)
+{
+ tcp_push_pending_frames(sk);
+ tcp_check_space(sk);
+}
+
+/*
+ * Check if sending an ack is needed.
+ */
+static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ /* More than one full frame received... */
+ if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss &&
+ /* ... and right edge of window advances far enough.
+ * (tcp_recvmsg() will send ACK otherwise). Or...
+ */
+ __tcp_select_window(sk) >= tp->rcv_wnd) ||
+ /* We ACK each frame or... */
+ tcp_in_quickack_mode(sk) ||
+ /* We have out of order data. */
+ (ofo_possible && skb_peek(&tp->out_of_order_queue))) {
+ /* Then ack it now */
+ tcp_send_ack(sk);
+ } else {
+ /* Else, send delayed ack. */
+ tcp_send_delayed_ack(sk);
+ }
+}
+
+static inline void tcp_ack_snd_check(struct sock *sk)
+{
+ if (!inet_csk_ack_scheduled(sk)) {
+ /* We sent a data segment already. */
+ return;
+ }
+ __tcp_ack_snd_check(sk, 1);
+}
+
+/*
+ * This routine is only called when we have urgent data
+ * signaled. Its the 'slow' part of tcp_urg. It could be
+ * moved inline now as tcp_urg is only called from one
+ * place. We handle URGent data wrong. We have to - as
+ * BSD still doesn't use the correction from RFC961.
+ * For 1003.1g we should support a new option TCP_STDURG to permit
+ * either form (or just set the sysctl tcp_stdurg).
+ */
+
+static void tcp_check_urg(struct sock *sk, const struct tcphdr *th)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ u32 ptr = ntohs(th->urg_ptr);
+
+ if (ptr && !sysctl_tcp_stdurg)
+ ptr--;
+ ptr += ntohl(th->seq);
+
+ /* Ignore urgent data that we've already seen and read. */
+ if (after(tp->copied_seq, ptr))
+ return;
+
+ /* Do not replay urg ptr.
+ *
+ * NOTE: interesting situation not covered by specs.
+ * Misbehaving sender may send urg ptr, pointing to segment,
+ * which we already have in ofo queue. We are not able to fetch
+ * such data and will stay in TCP_URG_NOTYET until will be eaten
+ * by recvmsg(). Seems, we are not obliged to handle such wicked
+ * situations. But it is worth to think about possibility of some
+ * DoSes using some hypothetical application level deadlock.
+ */
+ if (before(ptr, tp->rcv_nxt))
+ return;
+
+ /* Do we already have a newer (or duplicate) urgent pointer? */
+ if (tp->urg_data && !after(ptr, tp->urg_seq))
+ return;
+
+ /* Tell the world about our new urgent pointer. */
+ sk_send_sigurg(sk);
+
+ /* We may be adding urgent data when the last byte read was
+ * urgent. To do this requires some care. We cannot just ignore
+ * tp->copied_seq since we would read the last urgent byte again
+ * as data, nor can we alter copied_seq until this data arrives
+ * or we break the semantics of SIOCATMARK (and thus sockatmark())
+ *
+ * NOTE. Double Dutch. Rendering to plain English: author of comment
+ * above did something sort of send("A", MSG_OOB); send("B", MSG_OOB);
+ * and expect that both A and B disappear from stream. This is _wrong_.
+ * Though this happens in BSD with high probability, this is occasional.
+ * Any application relying on this is buggy. Note also, that fix "works"
+ * only in this artificial test. Insert some normal data between A and B and we will
+ * decline of BSD again. Verdict: it is better to remove to trap
+ * buggy users.
+ */
+ if (tp->urg_seq == tp->copied_seq && tp->urg_data &&
+ !sock_flag(sk, SOCK_URGINLINE) && tp->copied_seq != tp->rcv_nxt) {
+ struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
+ tp->copied_seq++;
+ if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) {
+ __skb_unlink(skb, &sk->sk_receive_queue);
+ __kfree_skb(skb);
+ }
+ }
+
+ tp->urg_data = TCP_URG_NOTYET;
+ tp->urg_seq = ptr;
+
+ /* Disable header prediction. */
+ tp->pred_flags = 0;
+}
+
+/* This is the 'fast' part of urgent handling. */
+static void tcp_urg(struct sock *sk, struct sk_buff *skb, const struct tcphdr *th)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ /* Check if we get a new urgent pointer - normally not. */
+ if (th->urg)
+ tcp_check_urg(sk, th);
+
+ /* Do we wait for any urgent data? - normally not... */
+ if (tp->urg_data == TCP_URG_NOTYET) {
+ u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) -
+ th->syn;
+
+ /* Is the urgent pointer pointing into this packet? */
+ if (ptr < skb->len) {
+ u8 tmp;
+ if (skb_copy_bits(skb, ptr, &tmp, 1))
+ BUG();
+ tp->urg_data = TCP_URG_VALID | tmp;
+ if (!sock_flag(sk, SOCK_DEAD))
+ sk->sk_data_ready(sk, 0);
+ }
+ }
+}
+
+static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ int chunk = skb->len - hlen;
+ int err;
+
+ local_bh_enable();
+ if (skb_csum_unnecessary(skb))
+ err = skb_copy_datagram_iovec(skb, hlen, tp->ucopy.iov, chunk);
+ else
+ err = skb_copy_and_csum_datagram_iovec(skb, hlen,
+ tp->ucopy.iov);
+
+ if (!err) {
+ tp->ucopy.len -= chunk;
+ tp->copied_seq += chunk;
+ tcp_rcv_space_adjust(sk);
+ }
+
+ local_bh_disable();
+ return err;
+}
+
+static __sum16 __tcp_checksum_complete_user(struct sock *sk,
+ struct sk_buff *skb)
+{
+ __sum16 result;
+
+ if (sock_owned_by_user(sk)) {
+ local_bh_enable();
+ result = __tcp_checksum_complete(skb);
+ local_bh_disable();
+ } else {
+ result = __tcp_checksum_complete(skb);
+ }
+ return result;
+}
+
+static inline int tcp_checksum_complete_user(struct sock *sk,
+ struct sk_buff *skb)
+{
+ return !skb_csum_unnecessary(skb) &&
+ __tcp_checksum_complete_user(sk, skb);
+}
+
+#ifdef CONFIG_NET_DMA
+static int tcp_dma_try_early_copy(struct sock *sk, struct sk_buff *skb,
+ int hlen)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ int chunk = skb->len - hlen;
+ int dma_cookie;
+ int copied_early = 0;
+
+ if (tp->ucopy.wakeup)
+ return 0;
+
+ if (!tp->ucopy.dma_chan && tp->ucopy.pinned_list)
+ tp->ucopy.dma_chan = net_dma_find_channel();
+
+ if (tp->ucopy.dma_chan && skb_csum_unnecessary(skb)) {
+
+ dma_cookie = dma_skb_copy_datagram_iovec(tp->ucopy.dma_chan,
+ skb, hlen,
+ tp->ucopy.iov, chunk,
+ tp->ucopy.pinned_list);
+
+ if (dma_cookie < 0)
+ goto out;
+
+ tp->ucopy.dma_cookie = dma_cookie;
+ copied_early = 1;
+
+ tp->ucopy.len -= chunk;
+ tp->copied_seq += chunk;
+ tcp_rcv_space_adjust(sk);
+
+ if ((tp->ucopy.len == 0) ||
+ (tcp_flag_word(tcp_hdr(skb)) & TCP_FLAG_PSH) ||
+ (atomic_read(&sk->sk_rmem_alloc) > (sk->sk_rcvbuf >> 1))) {
+ tp->ucopy.wakeup = 1;
+ sk->sk_data_ready(sk, 0);
+ }
+ } else if (chunk > 0) {
+ tp->ucopy.wakeup = 1;
+ sk->sk_data_ready(sk, 0);
+ }
+out:
+ return copied_early;
+}
+#endif /* CONFIG_NET_DMA */
+
+/* Does PAWS and seqno based validation of an incoming segment, flags will
+ * play significant role here.
+ */
+static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
+ const struct tcphdr *th, int syn_inerr)
+{
+ const u8 *hash_location;
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ /* RFC1323: H1. Apply PAWS check first. */
+ if (tcp_fast_parse_options(skb, th, tp, &hash_location) &&
+ tp->rx_opt.saw_tstamp &&
+ tcp_paws_discard(sk, skb)) {
+ if (!th->rst) {
+ NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
+ tcp_send_dupack(sk, skb);
+ goto discard;
+ }
+ /* Reset is accepted even if it did not pass PAWS. */
+ }
+
+ /* Step 1: check sequence number */
+ if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
+ /* RFC793, page 37: "In all states except SYN-SENT, all reset
+ * (RST) segments are validated by checking their SEQ-fields."
+ * And page 69: "If an incoming segment is not acceptable,
+ * an acknowledgment should be sent in reply (unless the RST
+ * bit is set, if so drop the segment and return)".
+ */
+ if (!th->rst) {
+ if (th->syn)
+ goto syn_challenge;
+ tcp_send_dupack(sk, skb);
+ }
+ goto discard;
+ }
+
+ /* Step 2: check RST bit */
+ if (th->rst) {
+ /* RFC 5961 3.2 :
+ * If sequence number exactly matches RCV.NXT, then
+ * RESET the connection
+ * else
+ * Send a challenge ACK
+ */
+ if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt)
+ tcp_reset(sk);
+ else
+ tcp_send_challenge_ack(sk);
+ goto discard;
+ }
+
+ /* step 3: check security and precedence [ignored] */
+
+ /* step 4: Check for a SYN
+ * RFC 5691 4.2 : Send a challenge ack
+ */
+ if (th->syn) {
+syn_challenge:
+ if (syn_inerr)
+ TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
+ NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNCHALLENGE);
+ tcp_send_challenge_ack(sk);
+ goto discard;
+ }
+
+ return true;
+
+discard:
+ __kfree_skb(skb);
+ return false;
+}
+
+/*
+ * TCP receive function for the ESTABLISHED state.
+ *
+ * It is split into a fast path and a slow path. The fast path is
+ * disabled when:
+ * - A zero window was announced from us - zero window probing
+ * is only handled properly in the slow path.
+ * - Out of order segments arrived.
+ * - Urgent data is expected.
+ * - There is no buffer space left
+ * - Unexpected TCP flags/window values/header lengths are received
+ * (detected by checking the TCP header against pred_flags)
+ * - Data is sent in both directions. Fast path only supports pure senders
+ * or pure receivers (this means either the sequence number or the ack
+ * value must stay constant)
+ * - Unexpected TCP option.
+ *
+ * When these conditions are not satisfied it drops into a standard
+ * receive procedure patterned after RFC793 to handle all cases.
+ * The first three cases are guaranteed by proper pred_flags setting,
+ * the rest is checked inline. Fast processing is turned on in
+ * tcp_data_queue when everything is OK.
+ */
+int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
+ const struct tcphdr *th, unsigned int len)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ /*
+ * Header prediction.
+ * The code loosely follows the one in the famous
+ * "30 instruction TCP receive" Van Jacobson mail.
+ *
+ * Van's trick is to deposit buffers into socket queue
+ * on a device interrupt, to call tcp_recv function
+ * on the receive process context and checksum and copy
+ * the buffer to user space. smart...
+ *
+ * Our current scheme is not silly either but we take the
+ * extra cost of the net_bh soft interrupt processing...
+ * We do checksum and copy also but from device to kernel.
+ */
+
+ tp->rx_opt.saw_tstamp = 0;
+
+ /* pred_flags is 0xS?10 << 16 + snd_wnd
+ * if header_prediction is to be made
+ * 'S' will always be tp->tcp_header_len >> 2
+ * '?' will be 0 for the fast path, otherwise pred_flags is 0 to
+ * turn it off (when there are holes in the receive
+ * space for instance)
+ * PSH flag is ignored.
+ */
+
+ if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags &&
+ TCP_SKB_CB(skb)->seq == tp->rcv_nxt &&
+ !after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) {
+ int tcp_header_len = tp->tcp_header_len;
+
+ /* Timestamp header prediction: tcp_header_len
+ * is automatically equal to th->doff*4 due to pred_flags
+ * match.
+ */
+
+ /* Check timestamp */
+ if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) {
+ /* No? Slow path! */
+ if (!tcp_parse_aligned_timestamp(tp, th))
+ goto slow_path;
+
+ /* If PAWS failed, check it more carefully in slow path */
+ if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0)
+ goto slow_path;
+
+ /* DO NOT update ts_recent here, if checksum fails
+ * and timestamp was corrupted part, it will result
+ * in a hung connection since we will drop all
+ * future packets due to the PAWS test.
+ */
+ }
+
+ if (len <= tcp_header_len) {
+ /* Bulk data transfer: sender */
+ if (len == tcp_header_len) {
+ /* Predicted packet is in window by definition.
+ * seq == rcv_nxt and rcv_wup <= rcv_nxt.
+ * Hence, check seq<=rcv_wup reduces to:
+ */
+ if (tcp_header_len ==
+ (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
+ tp->rcv_nxt == tp->rcv_wup)
+ tcp_store_ts_recent(tp);
+
+ /* We know that such packets are checksummed
+ * on entry.
+ */
+ tcp_ack(sk, skb, 0);
+ __kfree_skb(skb);
+ tcp_data_snd_check(sk);
+ return 0;
+ } else { /* Header too small */
+ TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
+ goto discard;
+ }
+ } else {
+ int eaten = 0;
+ int copied_early = 0;
+
+ if (tp->copied_seq == tp->rcv_nxt &&
+ len - tcp_header_len <= tp->ucopy.len) {
+#ifdef CONFIG_NET_DMA
+ if (tp->ucopy.task == current &&
+ sock_owned_by_user(sk) &&
+ tcp_dma_try_early_copy(sk, skb, tcp_header_len)) {
+ copied_early = 1;
+ eaten = 1;
+ }
+#endif
+ if (tp->ucopy.task == current &&
+ sock_owned_by_user(sk) && !copied_early) {
+ __set_current_state(TASK_RUNNING);
+
+ if (!tcp_copy_to_iovec(sk, skb, tcp_header_len))
+ eaten = 1;
+ }
+ if (eaten) {
+ /* Predicted packet is in window by definition.
+ * seq == rcv_nxt and rcv_wup <= rcv_nxt.
+ * Hence, check seq<=rcv_wup reduces to:
+ */
+ if (tcp_header_len ==
+ (sizeof(struct tcphdr) +
+ TCPOLEN_TSTAMP_ALIGNED) &&
+ tp->rcv_nxt == tp->rcv_wup)
+ tcp_store_ts_recent(tp);
+
+ tcp_rcv_rtt_measure_ts(sk, skb);
+
+ __skb_pull(skb, tcp_header_len);
+ tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
+ NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPHITSTOUSER);
+ }
+ if (copied_early)
+ tcp_cleanup_rbuf(sk, skb->len);
+ }
+ if (!eaten) {
+ if (tcp_checksum_complete_user(sk, skb))
+ goto csum_error;
+
+ if ((int)skb->truesize > sk->sk_forward_alloc)
+ goto step5;
+
+ /* Predicted packet is in window by definition.
+ * seq == rcv_nxt and rcv_wup <= rcv_nxt.
+ * Hence, check seq<=rcv_wup reduces to:
+ */
+ if (tcp_header_len ==
+ (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
+ tp->rcv_nxt == tp->rcv_wup)
+ tcp_store_ts_recent(tp);
+
+ tcp_rcv_rtt_measure_ts(sk, skb);
+
+ NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPHITS);
+
+ /* Bulk data transfer: receiver */
+ __skb_pull(skb, tcp_header_len);
+ __skb_queue_tail(&sk->sk_receive_queue, skb);
+ skb_set_owner_r(skb, sk);
+ tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
+ }
+
+ tcp_event_data_recv(sk, skb);
+
+ if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) {
+ /* Well, only one small jumplet in fast path... */
+ tcp_ack(sk, skb, FLAG_DATA);
+ tcp_data_snd_check(sk);
+ if (!inet_csk_ack_scheduled(sk))
+ goto no_ack;
+ }
+
+ if (!copied_early || tp->rcv_nxt != tp->rcv_wup)
+ __tcp_ack_snd_check(sk, 0);
+no_ack:
+#ifdef CONFIG_NET_DMA
+ if (copied_early)
+ __skb_queue_tail(&sk->sk_async_wait_queue, skb);
+ else
+#endif
+ if (eaten)
+ __kfree_skb(skb);
+ else
+ sk->sk_data_ready(sk, 0);
+ return 0;
+ }
+ }
+
+slow_path:
+ if (len < (th->doff << 2) || tcp_checksum_complete_user(sk, skb))
+ goto csum_error;
+
+ /*
+ * Standard slow path.
+ */
+
+ if (!tcp_validate_incoming(sk, skb, th, 1))
+ return 0;
+
+step5:
+ if (th->ack &&
+ tcp_ack(sk, skb, FLAG_SLOWPATH | FLAG_UPDATE_TS_RECENT) < 0)
+ goto discard;
+
+ tcp_rcv_rtt_measure_ts(sk, skb);
+
+ /* Process urgent data. */
+ tcp_urg(sk, skb, th);
+
+ /* step 7: process the segment text */
+ tcp_data_queue(sk, skb);
+
+ tcp_data_snd_check(sk);
+ tcp_ack_snd_check(sk);
+ return 0;
+
+csum_error:
+ TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
+
+discard:
+ __kfree_skb(skb);
+ return 0;
+}
+EXPORT_SYMBOL(tcp_rcv_established);
+
+static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
+ const struct tcphdr *th, unsigned int len)
+{
+ const u8 *hash_location;
+ struct inet_connection_sock *icsk = inet_csk(sk);
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct tcp_cookie_values *cvp = tp->cookie_values;
+ int saved_clamp = tp->rx_opt.mss_clamp;
+
+ tcp_parse_options(skb, &tp->rx_opt, &hash_location, 0);
+
+ if (th->ack) {
+ /* rfc793:
+ * "If the state is SYN-SENT then
+ * first check the ACK bit
+ * If the ACK bit is set
+ * If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send
+ * a reset (unless the RST bit is set, if so drop
+ * the segment and return)"
+ *
+ * We do not send data with SYN, so that RFC-correct
+ * test reduces to:
+ */
+ if (TCP_SKB_CB(skb)->ack_seq != tp->snd_nxt)
+ goto reset_and_undo;
+
+ if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
+ !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp,
+ tcp_time_stamp)) {
+ NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PAWSACTIVEREJECTED);
+ goto reset_and_undo;
+ }
+
+ /* Now ACK is acceptable.
+ *
+ * "If the RST bit is set
+ * If the ACK was acceptable then signal the user "error:
+ * connection reset", drop the segment, enter CLOSED state,
+ * delete TCB, and return."
+ */
+
+ if (th->rst) {
+ tcp_reset(sk);
+ goto discard;
+ }
+
+ /* rfc793:
+ * "fifth, if neither of the SYN or RST bits is set then
+ * drop the segment and return."
+ *
+ * See note below!
+ * --ANK(990513)
+ */
+ if (!th->syn)
+ goto discard_and_undo;
+
+ /* rfc793:
+ * "If the SYN bit is on ...
+ * are acceptable then ...
+ * (our SYN has been ACKed), change the connection
+ * state to ESTABLISHED..."
+ */
+
+ TCP_ECN_rcv_synack(tp, th);
+
+ tp->snd_wl1 = TCP_SKB_CB(skb)->seq;
+ tcp_ack(sk, skb, FLAG_SLOWPATH);
+
+ /* Ok.. it's good. Set up sequence numbers and
+ * move to established.
+ */
+ tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
+ tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
+
+ /* RFC1323: The window in SYN & SYN/ACK segments is
+ * never scaled.
+ */
+ tp->snd_wnd = ntohs(th->window);
+ tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
+
+ if (!tp->rx_opt.wscale_ok) {
+ tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0;
+ tp->window_clamp = min(tp->window_clamp, 65535U);
+ }
+
+ if (tp->rx_opt.saw_tstamp) {
+ tp->rx_opt.tstamp_ok = 1;
+ tp->tcp_header_len =
+ sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
+ tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
+ tcp_store_ts_recent(tp);
+ } else {
+ tp->tcp_header_len = sizeof(struct tcphdr);
+ }
+
+ if (tcp_is_sack(tp) && sysctl_tcp_fack)
+ tcp_enable_fack(tp);
+
+ tcp_mtup_init(sk);
+ tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
+ tcp_initialize_rcv_mss(sk);
+
+ /* Remember, tcp_poll() does not lock socket!
+ * Change state from SYN-SENT only after copied_seq
+ * is initialized. */
+ tp->copied_seq = tp->rcv_nxt;
+
+ if (cvp != NULL &&
+ cvp->cookie_pair_size > 0 &&
+ tp->rx_opt.cookie_plus > 0) {
+ int cookie_size = tp->rx_opt.cookie_plus
+ - TCPOLEN_COOKIE_BASE;
+ int cookie_pair_size = cookie_size
+ + cvp->cookie_desired;
+
+ /* A cookie extension option was sent and returned.
+ * Note that each incoming SYNACK replaces the
+ * Responder cookie. The initial exchange is most
+ * fragile, as protection against spoofing relies
+ * entirely upon the sequence and timestamp (above).
+ * This replacement strategy allows the correct pair to
+ * pass through, while any others will be filtered via
+ * Responder verification later.
+ */
+ if (sizeof(cvp->cookie_pair) >= cookie_pair_size) {
+ memcpy(&cvp->cookie_pair[cvp->cookie_desired],
+ hash_location, cookie_size);
+ cvp->cookie_pair_size = cookie_pair_size;
+ }
+ }
+
+ smp_mb();
+ tcp_set_state(sk, TCP_ESTABLISHED);
+
+ security_inet_conn_established(sk, skb);
+
+ /* Make sure socket is routed, for correct metrics. */
+ icsk->icsk_af_ops->rebuild_header(sk);
+
+ tcp_init_metrics(sk);
+
+ tcp_init_congestion_control(sk);
+
+ /* Prevent spurious tcp_cwnd_restart() on first data
+ * packet.
+ */
+ tp->lsndtime = tcp_time_stamp;
+
+ tcp_init_buffer_space(sk);
+
+ if (sock_flag(sk, SOCK_KEEPOPEN))
+ inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp));
+
+ if (!tp->rx_opt.snd_wscale)
+ __tcp_fast_path_on(tp, tp->snd_wnd);
+ else
+ tp->pred_flags = 0;
+
+ if (!sock_flag(sk, SOCK_DEAD)) {
+ sk->sk_state_change(sk);
+ sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
+ }
+
+ if (sk->sk_write_pending ||
+ icsk->icsk_accept_queue.rskq_defer_accept ||
+ icsk->icsk_ack.pingpong) {
+ /* Save one ACK. Data will be ready after
+ * several ticks, if write_pending is set.
+ *
+ * It may be deleted, but with this feature tcpdumps
+ * look so _wonderfully_ clever, that I was not able
+ * to stand against the temptation 8) --ANK
+ */
+ inet_csk_schedule_ack(sk);
+ icsk->icsk_ack.lrcvtime = tcp_time_stamp;
+ icsk->icsk_ack.ato = TCP_ATO_MIN;
+ tcp_incr_quickack(sk);
+ tcp_enter_quickack_mode(sk);
+ inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
+ TCP_DELACK_MAX, TCP_RTO_MAX);
+
+discard:
+ __kfree_skb(skb);
+ return 0;
+ } else {
+ tcp_send_ack(sk);
+ }
+ return -1;
+ }
+
+ /* No ACK in the segment */
+
+ if (th->rst) {
+ /* rfc793:
+ * "If the RST bit is set
+ *
+ * Otherwise (no ACK) drop the segment and return."
+ */
+
+ goto discard_and_undo;
+ }
+
+ /* PAWS check. */
+ if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp &&
+ tcp_paws_reject(&tp->rx_opt, 0))
+ goto discard_and_undo;
+
+ if (th->syn) {
+ /* We see SYN without ACK. It is attempt of
+ * simultaneous connect with crossed SYNs.
+ * Particularly, it can be connect to self.
+ */
+ tcp_set_state(sk, TCP_SYN_RECV);
+
+ if (tp->rx_opt.saw_tstamp) {
+ tp->rx_opt.tstamp_ok = 1;
+ tcp_store_ts_recent(tp);
+ tp->tcp_header_len =
+ sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
+ } else {
+ tp->tcp_header_len = sizeof(struct tcphdr);
+ }
+
+ tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
+ tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
+
+ /* RFC1323: The window in SYN & SYN/ACK segments is
+ * never scaled.
+ */
+ tp->snd_wnd = ntohs(th->window);
+ tp->snd_wl1 = TCP_SKB_CB(skb)->seq;
+ tp->max_window = tp->snd_wnd;
+
+ TCP_ECN_rcv_syn(tp, th);
+
+ tcp_mtup_init(sk);
+ tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
+ tcp_initialize_rcv_mss(sk);
+
+ tcp_send_synack(sk);
+#if 0
+ /* Note, we could accept data and URG from this segment.
+ * There are no obstacles to make this.
+ *
+ * However, if we ignore data in ACKless segments sometimes,
+ * we have no reasons to accept it sometimes.
+ * Also, seems the code doing it in step6 of tcp_rcv_state_process
+ * is not flawless. So, discard packet for sanity.
+ * Uncomment this return to process the data.
+ */
+ return -1;
+#else
+ goto discard;
+#endif
+ }
+ /* "fifth, if neither of the SYN or RST bits is set then
+ * drop the segment and return."
+ */
+
+discard_and_undo:
+ tcp_clear_options(&tp->rx_opt);
+ tp->rx_opt.mss_clamp = saved_clamp;
+ goto discard;
+
+reset_and_undo:
+ tcp_clear_options(&tp->rx_opt);
+ tp->rx_opt.mss_clamp = saved_clamp;
+ return 1;
+}
+
+/*
+ * This function implements the receiving procedure of RFC 793 for
+ * all states except ESTABLISHED and TIME_WAIT.
+ * It's called from both tcp_v4_rcv and tcp_v6_rcv and should be
+ * address independent.
+ */
+
+int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
+ const struct tcphdr *th, unsigned int len)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct inet_connection_sock *icsk = inet_csk(sk);
+ int queued = 0;
+
+ tp->rx_opt.saw_tstamp = 0;
+
+ switch (sk->sk_state) {
+ case TCP_CLOSE:
+ goto discard;
+
+ case TCP_LISTEN:
+ if (th->ack)
+ return 1;
+
+ if (th->rst)
+ goto discard;
+
+ if (th->syn) {
+ if (th->fin)
+ goto discard;
+ if (icsk->icsk_af_ops->conn_request(sk, skb) < 0)
+ return 1;
+
+ /* Now we have several options: In theory there is
+ * nothing else in the frame. KA9Q has an option to
+ * send data with the syn, BSD accepts data with the
+ * syn up to the [to be] advertised window and
+ * Solaris 2.1 gives you a protocol error. For now
+ * we just ignore it, that fits the spec precisely
+ * and avoids incompatibilities. It would be nice in
+ * future to drop through and process the data.
+ *
+ * Now that TTCP is starting to be used we ought to
+ * queue this data.
+ * But, this leaves one open to an easy denial of
+ * service attack, and SYN cookies can't defend
+ * against this problem. So, we drop the data
+ * in the interest of security over speed unless
+ * it's still in use.
+ */
+ kfree_skb(skb);
+ return 0;
+ }
+ goto discard;
+
+ case TCP_SYN_SENT:
+ queued = tcp_rcv_synsent_state_process(sk, skb, th, len);
+ if (queued >= 0)
+ return queued;
+
+ /* Do step6 onward by hand. */
+ tcp_urg(sk, skb, th);
+ __kfree_skb(skb);
+ tcp_data_snd_check(sk);
+ return 0;
+ }
+
+ if (!tcp_validate_incoming(sk, skb, th, 0))
+ return 0;
+
+ /* step 5: check the ACK field */
+ if (th->ack) {
+ int acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH |
+ FLAG_UPDATE_TS_RECENT) > 0;
+
+ switch (sk->sk_state) {
+ case TCP_SYN_RECV:
+ if (acceptable) {
+ tp->copied_seq = tp->rcv_nxt;
+ smp_mb();
+ tcp_set_state(sk, TCP_ESTABLISHED);
+ sk->sk_state_change(sk);
+
+ /* Note, that this wakeup is only for marginal
+ * crossed SYN case. Passively open sockets
+ * are not waked up, because sk->sk_sleep ==
+ * NULL and sk->sk_socket == NULL.
+ */
+ if (sk->sk_socket)
+ sk_wake_async(sk,
+ SOCK_WAKE_IO, POLL_OUT);
+
+ tp->snd_una = TCP_SKB_CB(skb)->ack_seq;
+ tp->snd_wnd = ntohs(th->window) <<
+ tp->rx_opt.snd_wscale;
+ tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
+
+ if (tp->rx_opt.tstamp_ok)
+ tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
+
+ /* Make sure socket is routed, for
+ * correct metrics.
+ */
+ icsk->icsk_af_ops->rebuild_header(sk);
+
+ tcp_init_metrics(sk);
+
+ tcp_init_congestion_control(sk);
+
+ /* Prevent spurious tcp_cwnd_restart() on
+ * first data packet.
+ */
+ tp->lsndtime = tcp_time_stamp;
+
+ tcp_mtup_init(sk);
+ tcp_initialize_rcv_mss(sk);
+ tcp_init_buffer_space(sk);
+ tcp_fast_path_on(tp);
+ } else {
+ return 1;
+ }
+ break;
+
+ case TCP_FIN_WAIT1:
+ if (tp->snd_una == tp->write_seq) {
+ tcp_set_state(sk, TCP_FIN_WAIT2);
+ sk->sk_shutdown |= SEND_SHUTDOWN;
+ dst_confirm(__sk_dst_get(sk));
+
+ if (!sock_flag(sk, SOCK_DEAD))
+ /* Wake up lingering close() */
+ sk->sk_state_change(sk);
+ else {
+ int tmo;
+
+ if (tp->linger2 < 0 ||
+ (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
+ after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt))) {
+ tcp_done(sk);
+ NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
+ return 1;
+ }
+
+ tmo = tcp_fin_time(sk);
+ if (tmo > TCP_TIMEWAIT_LEN) {
+ inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN);
+ } else if (th->fin || sock_owned_by_user(sk)) {
+ /* Bad case. We could lose such FIN otherwise.
+ * It is not a big problem, but it looks confusing
+ * and not so rare event. We still can lose it now,
+ * if it spins in bh_lock_sock(), but it is really
+ * marginal case.
+ */
+ inet_csk_reset_keepalive_timer(sk, tmo);
+ } else {
+ tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
+ goto discard;
+ }
+ }
+ }
+ break;
+
+ case TCP_CLOSING:
+ if (tp->snd_una == tp->write_seq) {
+ tcp_time_wait(sk, TCP_TIME_WAIT, 0);
+ goto discard;
+ }
+ break;
+
+ case TCP_LAST_ACK:
+ if (tp->snd_una == tp->write_seq) {
+ tcp_update_metrics(sk);
+ tcp_done(sk);
+ goto discard;
+ }
+ break;
+ }
+ } else
+ goto discard;
+
+ /* step 6: check the URG bit */
+ tcp_urg(sk, skb, th);
+
+ /* step 7: process the segment text */
+ switch (sk->sk_state) {
+ case TCP_CLOSE_WAIT:
+ case TCP_CLOSING:
+ case TCP_LAST_ACK:
+ if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
+ break;
+ case TCP_FIN_WAIT1:
+ case TCP_FIN_WAIT2:
+ /* RFC 793 says to queue data in these states,
+ * RFC 1122 says we MUST send a reset.
+ * BSD 4.4 also does reset.
+ */
+ if (sk->sk_shutdown & RCV_SHUTDOWN) {
+ if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
+ after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
+ NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
+ tcp_reset(sk);
+ return 1;
+ }
+ }
+ /* Fall through */
+ case TCP_ESTABLISHED:
+ tcp_data_queue(sk, skb);
+ queued = 1;
+ break;
+ }
+
+ /* tcp_data could move socket to TIME-WAIT */
+ if (sk->sk_state != TCP_CLOSE) {
+ tcp_data_snd_check(sk);
+ tcp_ack_snd_check(sk);
+ }
+
+ if (!queued) {
+discard:
+ __kfree_skb(skb);
+ }
+ return 0;
+}
+EXPORT_SYMBOL(tcp_rcv_state_process);