lckpwdf.c 5.1 KB

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  1. /* vi: set sw=4 ts=4: */
  2. /* Handle locking of password file.
  3. Copyright (C) 1996,98,2000,02 Free Software Foundation, Inc.
  4. This file is part of the GNU C Library.
  5. Contributed by Ulrich Drepper <drepper@cygnus.com>, 1996.
  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. The GNU C Library is distributed in the hope that it will be useful,
  11. but WITHOUT ANY WARRANTY; without even the implied warranty of
  12. MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  13. Lesser General Public License for more details.
  14. You should have received a copy of the GNU Lesser General Public
  15. License along with the GNU C Library; if not, write to the Free
  16. Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  17. 02111-1307 USA. */
  18. #include <features.h>
  19. #include <fcntl.h>
  20. #include <signal.h>
  21. #include <string.h>
  22. #include <unistd.h>
  23. #include <sys/file.h>
  24. #include <paths.h>
  25. #include <shadow.h>
  26. /* Experimentally off - libc_hidden_proto(memset) */
  27. libc_hidden_proto(open)
  28. libc_hidden_proto(fcntl)
  29. libc_hidden_proto(close)
  30. libc_hidden_proto(sigfillset)
  31. libc_hidden_proto(sigaction)
  32. libc_hidden_proto(sigprocmask)
  33. libc_hidden_proto(sigaddset)
  34. libc_hidden_proto(sigemptyset)
  35. libc_hidden_proto(alarm)
  36. /* How long to wait for getting the lock before returning with an
  37. error. */
  38. #define TIMEOUT 15 /* sec */
  39. /* File descriptor for lock file. */
  40. static int lock_fd = -1;
  41. /* Prevent problems in multithreaded program by using mutex. */
  42. #include <bits/uClibc_mutex.h>
  43. __UCLIBC_MUTEX_STATIC(mylock, PTHREAD_MUTEX_INITIALIZER);
  44. /* Prototypes for local functions. */
  45. static void noop_handler (int __sig);
  46. int
  47. lckpwdf (void)
  48. {
  49. int flags;
  50. sigset_t saved_set; /* Saved set of caught signals. */
  51. struct sigaction saved_act; /* Saved signal action. */
  52. sigset_t new_set; /* New set of caught signals. */
  53. struct sigaction new_act; /* New signal action. */
  54. struct flock fl; /* Information struct for locking. */
  55. int result;
  56. int rv = -1;
  57. if (lock_fd != -1)
  58. /* Still locked by own process. */
  59. return -1;
  60. /* Prevent problems caused by multiple threads. */
  61. __UCLIBC_MUTEX_LOCK(mylock);
  62. lock_fd = open (_PATH_PASSWD, O_WRONLY);
  63. if (lock_fd == -1) {
  64. /* Cannot create lock file. */
  65. goto DONE;
  66. }
  67. /* Make sure file gets correctly closed when process finished. */
  68. flags = fcntl (lock_fd, F_GETFD, 0);
  69. if (flags == -1) {
  70. /* Cannot get file flags. */
  71. close(lock_fd);
  72. lock_fd = -1;
  73. goto DONE;
  74. }
  75. flags |= FD_CLOEXEC; /* Close on exit. */
  76. if (fcntl (lock_fd, F_SETFD, flags) < 0) {
  77. /* Cannot set new flags. */
  78. close(lock_fd);
  79. lock_fd = -1;
  80. goto DONE;
  81. }
  82. /* Now we have to get exclusive write access. Since multiple
  83. process could try this we won't stop when it first fails.
  84. Instead we set a timeout for the system call. Once the timer
  85. expires it is likely that there are some problems which cannot be
  86. resolved by waiting.
  87. It is important that we don't change the signal state. We must
  88. restore the old signal behaviour. */
  89. memset (&new_act, '\0', sizeof (struct sigaction));
  90. new_act.sa_handler = noop_handler;
  91. sigfillset (&new_act.sa_mask);
  92. new_act.sa_flags = 0ul;
  93. /* Install new action handler for alarm and save old. */
  94. if (sigaction (SIGALRM, &new_act, &saved_act) < 0) {
  95. /* Cannot install signal handler. */
  96. close(lock_fd);
  97. lock_fd = -1;
  98. goto DONE;
  99. }
  100. /* Now make sure the alarm signal is not blocked. */
  101. sigemptyset (&new_set);
  102. sigaddset (&new_set, SIGALRM);
  103. if (sigprocmask (SIG_UNBLOCK, &new_set, &saved_set) < 0) {
  104. sigaction (SIGALRM, &saved_act, NULL);
  105. close(lock_fd);
  106. lock_fd = -1;
  107. goto DONE;
  108. }
  109. /* Start timer. If we cannot get the lock in the specified time we
  110. get a signal. */
  111. alarm (TIMEOUT);
  112. /* Try to get the lock. */
  113. memset (&fl, '\0', sizeof (struct flock));
  114. fl.l_type = F_WRLCK;
  115. fl.l_whence = SEEK_SET;
  116. result = fcntl (lock_fd, F_SETLKW, &fl);
  117. /* Clear alarm. */
  118. alarm (0);
  119. /* Restore old set of handled signals. We don't need to know
  120. about the current one.*/
  121. sigprocmask (SIG_SETMASK, &saved_set, NULL);
  122. /* Restore old action handler for alarm. We don't need to know
  123. about the current one. */
  124. sigaction (SIGALRM, &saved_act, NULL);
  125. if (result < 0) {
  126. close(lock_fd);
  127. lock_fd = -1;
  128. goto DONE;
  129. }
  130. rv = 0;
  131. DONE:
  132. __UCLIBC_MUTEX_UNLOCK(mylock);
  133. return 0;
  134. }
  135. int
  136. ulckpwdf (void)
  137. {
  138. int result;
  139. if (lock_fd == -1)
  140. /* There is no lock set. */
  141. result = -1;
  142. else
  143. {
  144. /* Prevent problems caused by multiple threads. */
  145. __UCLIBC_MUTEX_LOCK(mylock);
  146. result = close (lock_fd);
  147. /* Mark descriptor as unused. */
  148. lock_fd = -1;
  149. /* Clear mutex. */
  150. __UCLIBC_MUTEX_UNLOCK(mylock);
  151. }
  152. return result;
  153. }
  154. static void
  155. noop_handler (int sig)
  156. {
  157. /* We simply return which makes the `fcntl' call return with an error. */
  158. }