shadow/lckpwdf.c

   1 /* Handle locking of password file.
   2    Copyright (C) 1996 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 Library General Public License as
   8    published by the Free Software Foundation; either version 2 of the
   9    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    Library General Public License for more details.
  15
  16    You should have received a copy of the GNU Library General Public
  17    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  18    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  19    Boston, MA 02111-1307, USA.  */
  20
  21 #include <fcntl.h>
  22 #include <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 __P ((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 ()
  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   int result;
  90
  91   if (lock_fd != -1)
  92     /* Still locked by own process.  */
  93     return -1;
  94
  95   /* Prevent problems caused by multiple threads.  */
  96   __libc_lock_lock (lock);
  97
  98   lock_fd = open (PWD_LOCKFILE, O_WRONLY | O_CREAT, 0600);
  99   if (lock_fd == -1)
 100     /* Cannot create lock file.  */
 101     RETURN_CLOSE_FD (-1);
 102
 103   /* Make sure file gets correctly closed when process finished.  */
 104   flags = fcntl (lock_fd, F_GETFD, 0);
 105   if (flags == -1)
 106     /* Cannot get file flags.  */
 107     RETURN_CLOSE_FD (-1);
 108   flags |= FD_CLOEXEC;          /* Close on exit.  */
 109   if (fcntl (lock_fd, F_SETFD, flags) < 0)
 110     /* Cannot set new flags.  */
 111     RETURN_CLOSE_FD (-1);
 112
 113   /* Now we have to get exclusive write access.  Since multiple
 114      process could try this we won't stop when it first fails.
 115      Instead we set a timeout for the system call.  Once the timer
 116      expires it is likely that there are some problems which cannot be
 117      resolved by waiting.
 118
 119      It is important that we don't change the signal state.  We must
 120      restore the old signal behaviour.  */
 121   memset (&new_act, '\0', sizeof (struct sigaction));
 122   new_act.sa_handler = noop_handler;
 123   sigfillset (&new_act.sa_mask);
 124   new_act.sa_flags = 0ul;
 125
 126   /* Install new action handler for alarm and save old.  */
 127   if (sigaction (SIGALRM, &new_act, &saved_act) < 0)
 128     /* Cannot install signal handler.  */
 129     RETURN_CLOSE_FD (-1);
 130
 131   /* Now make sure the alarm signal is not blocked.  */
 132   sigemptyset (&new_set);
 133   sigaddset (&new_set, SIGALRM);
 134   if (sigprocmask (SIG_UNBLOCK, &new_set, &saved_set) < 0)
 135     RETURN_RESTORE_HANDLER (-1);
 136
 137   /* Start timer.  If we cannot get the lock in the specified time we
 138      get a signal.  */
 139   alarm (TIMEOUT);
 140
 141   /* Try to get the lock.  */
 142   result = flock (lock_fd, LOCK_EX);
 143
 144   RETURN_CLEAR_ALARM (result);
 145 }
 146 weak_alias (__lckpwdf, lckpwdf)
 147
 148
 149 int
 150 __ulckpwdf ()
 151 {
 152   int result;
 153
 154   if (lock_fd == -1)
 155     /* There is no lock set.  */
 156     result = -1;
 157   else
 158     {
 159       /* Prevent problems caused by multiple threads.  */
 160       __libc_lock_lock (lock);
 161
 162       result = close (lock_fd);
 163
 164       /* Mark descriptor as unused.  */
 165       lock_fd = -1;
 166
 167       /* Clear mutex.  */
 168       __libc_lock_unlock (lock);
 169     }
 170
 171   return result;
 172 }
 173 weak_alias (__ulckpwdf, ulckpwdf)
 174
 175
 176 static void
 177 noop_handler (sig)
 178      int sig;
 179 {
 180   /* We simply return which makes the `flock' call return with an error.  */
 181 }