lh | 9ed821d | 2023-04-07 01:36:19 -0700 | [diff] [blame^] | 1 | /* Handle locking of password file. |
| 2 | Copyright (C) 1996-2015 Free Software Foundation, Inc. |
| 3 | This file is part of the GNU C Library. |
| 4 | Contributed by Ulrich Drepper <drepper@cygnus.com>, 1996. |
| 5 | |
| 6 | The GNU C Library is free software; you can redistribute it and/or |
| 7 | modify it under the terms of the GNU Lesser General Public |
| 8 | License as published by the Free Software Foundation; either |
| 9 | version 2.1 of the License, or (at your option) any later version. |
| 10 | |
| 11 | The GNU C Library is distributed in the hope that it will be useful, |
| 12 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 13 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| 14 | Lesser General Public License for more details. |
| 15 | |
| 16 | You should have received a copy of the GNU Lesser General Public |
| 17 | License along with the GNU C Library; if not, see |
| 18 | <http://www.gnu.org/licenses/>. */ |
| 19 | |
| 20 | #include <fcntl.h> |
| 21 | #include <bits/libc-lock.h> |
| 22 | #include <shadow.h> |
| 23 | #include <signal.h> |
| 24 | #include <string.h> |
| 25 | #include <unistd.h> |
| 26 | #include <sys/file.h> |
| 27 | |
| 28 | #include <kernel-features.h> |
| 29 | |
| 30 | |
| 31 | /* Name of the lock file. */ |
| 32 | #define PWD_LOCKFILE "/etc/.pwd.lock" |
| 33 | |
| 34 | /* How long to wait for getting the lock before returning with an |
| 35 | error. */ |
| 36 | #define TIMEOUT 15 /* sec */ |
| 37 | |
| 38 | |
| 39 | /* File descriptor for lock file. */ |
| 40 | static int lock_fd = -1; |
| 41 | |
| 42 | /* Prevent problems in multithreaded program by using mutex. */ |
| 43 | __libc_lock_define_initialized (static, lock) |
| 44 | |
| 45 | |
| 46 | /* Prototypes for local functions. */ |
| 47 | static void noop_handler (int __sig); |
| 48 | |
| 49 | |
| 50 | /* We cannot simply return in error cases. We have to close the file |
| 51 | and perhaps restore the signal handler. */ |
| 52 | #define RETURN_CLOSE_FD(code) \ |
| 53 | do { \ |
| 54 | if ((code) < 0 && lock_fd >= 0) \ |
| 55 | { \ |
| 56 | __close (lock_fd); \ |
| 57 | lock_fd = -1; \ |
| 58 | } \ |
| 59 | __libc_lock_unlock (lock); \ |
| 60 | return (code); \ |
| 61 | } while (0) |
| 62 | |
| 63 | #define RETURN_RESTORE_HANDLER(code) \ |
| 64 | do { \ |
| 65 | /* Restore old action handler for alarm. We don't need to know \ |
| 66 | about the current one. */ \ |
| 67 | __sigaction (SIGALRM, &saved_act, NULL); \ |
| 68 | RETURN_CLOSE_FD (code); \ |
| 69 | } while (0) |
| 70 | |
| 71 | #define RETURN_CLEAR_ALARM(code) \ |
| 72 | do { \ |
| 73 | /* Clear alarm. */ \ |
| 74 | alarm (0); \ |
| 75 | /* Restore old set of handled signals. We don't need to know \ |
| 76 | about the current one.*/ \ |
| 77 | __sigprocmask (SIG_SETMASK, &saved_set, NULL); \ |
| 78 | RETURN_RESTORE_HANDLER (code); \ |
| 79 | } while (0) |
| 80 | |
| 81 | |
| 82 | int |
| 83 | __lckpwdf (void) |
| 84 | { |
| 85 | sigset_t saved_set; /* Saved set of caught signals. */ |
| 86 | struct sigaction saved_act; /* Saved signal action. */ |
| 87 | sigset_t new_set; /* New set of caught signals. */ |
| 88 | struct sigaction new_act; /* New signal action. */ |
| 89 | struct flock fl; /* Information struct for locking. */ |
| 90 | int result; |
| 91 | |
| 92 | if (lock_fd != -1) |
| 93 | /* Still locked by own process. */ |
| 94 | return -1; |
| 95 | |
| 96 | /* Prevent problems caused by multiple threads. */ |
| 97 | __libc_lock_lock (lock); |
| 98 | |
| 99 | int oflags = O_WRONLY | O_CREAT; |
| 100 | #ifdef O_CLOEXEC |
| 101 | oflags |= O_CLOEXEC; |
| 102 | #endif |
| 103 | lock_fd = __open (PWD_LOCKFILE, oflags, 0600); |
| 104 | if (lock_fd == -1) |
| 105 | /* Cannot create lock file. */ |
| 106 | RETURN_CLOSE_FD (-1); |
| 107 | |
| 108 | #ifndef __ASSUME_O_CLOEXEC |
| 109 | # ifdef O_CLOEXEC |
| 110 | if (__have_o_cloexec <= 0) |
| 111 | # endif |
| 112 | { |
| 113 | /* Make sure file gets correctly closed when process finished. */ |
| 114 | int flags = __fcntl (lock_fd, F_GETFD, 0); |
| 115 | if (flags == -1) |
| 116 | /* Cannot get file flags. */ |
| 117 | RETURN_CLOSE_FD (-1); |
| 118 | # ifdef O_CLOEXEC |
| 119 | if (__have_o_cloexec == 0) |
| 120 | __have_o_cloexec = (flags & FD_CLOEXEC) == 0 ? -1 : 1; |
| 121 | if (__have_o_cloexec < 0) |
| 122 | # endif |
| 123 | { |
| 124 | flags |= FD_CLOEXEC; /* Close on exit. */ |
| 125 | if (__fcntl (lock_fd, F_SETFD, flags) < 0) |
| 126 | /* Cannot set new flags. */ |
| 127 | RETURN_CLOSE_FD (-1); |
| 128 | } |
| 129 | } |
| 130 | #endif |
| 131 | |
| 132 | /* Now we have to get exclusive write access. Since multiple |
| 133 | process could try this we won't stop when it first fails. |
| 134 | Instead we set a timeout for the system call. Once the timer |
| 135 | expires it is likely that there are some problems which cannot be |
| 136 | resolved by waiting. |
| 137 | |
| 138 | It is important that we don't change the signal state. We must |
| 139 | restore the old signal behaviour. */ |
| 140 | memset (&new_act, '\0', sizeof (struct sigaction)); |
| 141 | new_act.sa_handler = noop_handler; |
| 142 | __sigfillset (&new_act.sa_mask); |
| 143 | new_act.sa_flags = 0ul; |
| 144 | |
| 145 | /* Install new action handler for alarm and save old. */ |
| 146 | if (__sigaction (SIGALRM, &new_act, &saved_act) < 0) |
| 147 | /* Cannot install signal handler. */ |
| 148 | RETURN_CLOSE_FD (-1); |
| 149 | |
| 150 | /* Now make sure the alarm signal is not blocked. */ |
| 151 | __sigemptyset (&new_set); |
| 152 | __sigaddset (&new_set, SIGALRM); |
| 153 | if (__sigprocmask (SIG_UNBLOCK, &new_set, &saved_set) < 0) |
| 154 | RETURN_RESTORE_HANDLER (-1); |
| 155 | |
| 156 | /* Start timer. If we cannot get the lock in the specified time we |
| 157 | get a signal. */ |
| 158 | alarm (TIMEOUT); |
| 159 | |
| 160 | /* Try to get the lock. */ |
| 161 | memset (&fl, '\0', sizeof (struct flock)); |
| 162 | fl.l_type = F_WRLCK; |
| 163 | fl.l_whence = SEEK_SET; |
| 164 | result = __fcntl (lock_fd, F_SETLKW, &fl); |
| 165 | |
| 166 | RETURN_CLEAR_ALARM (result); |
| 167 | } |
| 168 | weak_alias (__lckpwdf, lckpwdf) |
| 169 | |
| 170 | |
| 171 | int |
| 172 | __ulckpwdf (void) |
| 173 | { |
| 174 | int result; |
| 175 | |
| 176 | if (lock_fd == -1) |
| 177 | /* There is no lock set. */ |
| 178 | result = -1; |
| 179 | else |
| 180 | { |
| 181 | /* Prevent problems caused by multiple threads. */ |
| 182 | __libc_lock_lock (lock); |
| 183 | |
| 184 | result = __close (lock_fd); |
| 185 | |
| 186 | /* Mark descriptor as unused. */ |
| 187 | lock_fd = -1; |
| 188 | |
| 189 | /* Clear mutex. */ |
| 190 | __libc_lock_unlock (lock); |
| 191 | } |
| 192 | |
| 193 | return result; |
| 194 | } |
| 195 | weak_alias (__ulckpwdf, ulckpwdf) |
| 196 | |
| 197 | |
| 198 | static void |
| 199 | noop_handler (int sig) |
| 200 | { |
| 201 | /* We simply return which makes the `fcntl' call return with an error. */ |
| 202 | } |