shadow/lckpwdf.c

   1 /* Handle locking of password file.
   2    Copyright (C) 1996,98,2000,02 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, write to the Free
  18    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19    02111-1307 USA.  */
  20
  21 #include <fcntl.h>
  22 #include <bits/libc-lock.h>
  23 #include <shadow.h>
  24 #include <signal.h>
  25 #include <string.h>
  26 #include <unistd.h>
  27 #include <sys/file.h>
  28
  29
  30 /* Name of the lock file.  */
  31 #define PWD_LOCKFILE "/etc/.pwd.lock"
  32
  33 /* How long to wait for getting the lock before returning with an
  34    error.  */
  35 #define TIMEOUT 15 /* sec */
  36
  37
  38 /* File descriptor for lock file.  */
  39 static int lock_fd = -1;
  40
  41 /* Prevent problems in multithreaded program by using mutex.  */
  42 __libc_lock_define_initialized (static, lock)
  43
  44
  45 /* Prototypes for local functions.  */
  46 static void noop_handler (int __sig);
  47
  48
  49 /* We cannot simply return in error cases.  We have to close the file
  50    and perhaps restore the signal handler.  */
  51 #define RETURN_CLOSE_FD(code)                                                 \
  52   do {                                                                        \
  53     if ((code) < 0 && lock_fd >= 0)                                           \
  54       {                                                                       \
  55         __close (lock_fd);                                                    \
  56         lock_fd = -1;                                                         \
  57       }                                                                       \
  58     __libc_lock_unlock (lock);                                                \
  59     return (code);                                                            \
  60   } while (0)
  61
  62 #define RETURN_RESTORE_HANDLER(code)                                          \
  63   do {                                                                        \
  64     /* Restore old action handler for alarm.  We don't need to know           \
  65        about the current one.  */                                             \
  66     __sigaction (SIGALRM, &saved_act, NULL);                                  \
  67     RETURN_CLOSE_FD (code);                                                   \
  68   } while (0)
  69
  70 #define RETURN_CLEAR_ALARM(code)                                              \
  71   do {                                                                        \
  72     /* Clear alarm.  */                                                       \
  73     alarm (0);                                                                \
  74     /* Restore old set of handled signals.  We don't need to know             \
  75        about the current one.*/                                               \
  76     __sigprocmask (SIG_SETMASK, &saved_set, NULL);                            \
  77     RETURN_RESTORE_HANDLER (code);                                            \
  78   } while (0)
  79
  80
  81 int
  82 __lckpwdf (void)
  83 {
  84   int flags;
  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   lock_fd = __open (PWD_LOCKFILE, O_WRONLY | O_CREAT, 0600);
 100   if (lock_fd == -1)
 101     /* Cannot create lock file.  */
 102     RETURN_CLOSE_FD (-1);
 103
 104   /* Make sure file gets correctly closed when process finished.  */
 105   flags = __fcntl (lock_fd, F_GETFD, 0);
 106   if (flags == -1)
 107     /* Cannot get file flags.  */
 108     RETURN_CLOSE_FD (-1);
 109   flags |= FD_CLOEXEC;          /* Close on exit.  */
 110   if (__fcntl (lock_fd, F_SETFD, flags) < 0)
 111     /* Cannot set new flags.  */
 112     RETURN_CLOSE_FD (-1);
 113
 114   /* Now we have to get exclusive write access.  Since multiple
 115      process could try this we won't stop when it first fails.
 116      Instead we set a timeout for the system call.  Once the timer
 117      expires it is likely that there are some problems which cannot be
 118      resolved by waiting.
 119
 120      It is important that we don't change the signal state.  We must
 121      restore the old signal behaviour.  */
 122   memset (&new_act, '\0', sizeof (struct sigaction));
 123   new_act.sa_handler = noop_handler;
 124   __sigfillset (&new_act.sa_mask);
 125   new_act.sa_flags = 0ul;
 126
 127   /* Install new action handler for alarm and save old.  */
 128   if (__sigaction (SIGALRM, &new_act, &saved_act) < 0)
 129     /* Cannot install signal handler.  */
 130     RETURN_CLOSE_FD (-1);
 131
 132   /* Now make sure the alarm signal is not blocked.  */
 133   __sigemptyset (&new_set);
 134   __sigaddset (&new_set, SIGALRM);
 135   if (__sigprocmask (SIG_UNBLOCK, &new_set, &saved_set) < 0)
 136     RETURN_RESTORE_HANDLER (-1);
 137
 138   /* Start timer.  If we cannot get the lock in the specified time we
 139      get a signal.  */
 140   alarm (TIMEOUT);
 141
 142   /* Try to get the lock.  */
 143   memset (&fl, '\0', sizeof (struct flock));
 144   fl.l_type = F_WRLCK;
 145   fl.l_whence = SEEK_SET;
 146   result = __fcntl (lock_fd, F_SETLKW, &fl);
 147
 148   RETURN_CLEAR_ALARM (result);
 149 }
 150 weak_alias (__lckpwdf, lckpwdf)
 151
 152
 153 int
 154 __ulckpwdf (void)
 155 {
 156   int result;
 157
 158   if (lock_fd == -1)
 159     /* There is no lock set.  */
 160     result = -1;
 161   else
 162     {
 163       /* Prevent problems caused by multiple threads.  */
 164       __libc_lock_lock (lock);
 165
 166       result = __close (lock_fd);
 167
 168       /* Mark descriptor as unused.  */
 169       lock_fd = -1;
 170
 171       /* Clear mutex.  */
 172       __libc_lock_unlock (lock);
 173     }
 174
 175   return result;
 176 }
 177 weak_alias (__ulckpwdf, ulckpwdf)
 178
 179
 180 static void
 181 noop_handler (int sig)
 182 {
 183   /* We simply return which makes the `fcntl' call return with an error.  */
 184 }