shadow/lckpwdf.c

   1 /* Handle locking of password file.
   2    Copyright (C) 1996,1998,2000,2002,2007,2009 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 #include <kernel-features.h>
  30
  31
  32 /* Name of the lock file.  */
  33 #define PWD_LOCKFILE "/etc/.pwd.lock"
  34
  35 /* How long to wait for getting the lock before returning with an
  36    error.  */
  37 #define TIMEOUT 15 /* sec */
  38
  39
  40 /* File descriptor for lock file.  */
  41 static int lock_fd = -1;
  42
  43 /* Prevent problems in multithreaded program by using mutex.  */
  44 __libc_lock_define_initialized (static, lock)
  45
  46
  47 /* Prototypes for local functions.  */
  48 static void noop_handler (int __sig);
  49
  50
  51 /* We cannot simply return in error cases.  We have to close the file
  52    and perhaps restore the signal handler.  */
  53 #define RETURN_CLOSE_FD(code)                                                 \
  54   do {                                                                        \
  55     if ((code) < 0 && lock_fd >= 0)                                           \
  56       {                                                                       \
  57         __close (lock_fd);                                                    \
  58         lock_fd = -1;                                                         \
  59       }                                                                       \
  60     __libc_lock_unlock (lock);                                                \
  61     return (code);                                                            \
  62   } while (0)
  63
  64 #define RETURN_RESTORE_HANDLER(code)                                          \
  65   do {                                                                        \
  66     /* Restore old action handler for alarm.  We don't need to know           \
  67        about the current one.  */                                             \
  68     __sigaction (SIGALRM, &saved_act, NULL);                                  \
  69     RETURN_CLOSE_FD (code);                                                   \
  70   } while (0)
  71
  72 #define RETURN_CLEAR_ALARM(code)                                              \
  73   do {                                                                        \
  74     /* Clear alarm.  */                                                       \
  75     alarm (0);                                                                \
  76     /* Restore old set of handled signals.  We don't need to know             \
  77        about the current one.*/                                               \
  78     __sigprocmask (SIG_SETMASK, &saved_set, NULL);                            \
  79     RETURN_RESTORE_HANDLER (code);                                            \
  80   } while (0)
  81
  82
  83 int
  84 __lckpwdf (void)
  85 {
  86   sigset_t saved_set;                   /* Saved set of caught signals.  */
  87   struct sigaction saved_act;           /* Saved signal action.  */
  88   sigset_t new_set;                     /* New set of caught signals.  */
  89   struct sigaction new_act;             /* New signal action.  */
  90   struct flock fl;                      /* Information struct for locking.  */
  91   int result;
  92
  93   if (lock_fd != -1)
  94     /* Still locked by own process.  */
  95     return -1;
  96
  97   /* Prevent problems caused by multiple threads.  */
  98   __libc_lock_lock (lock);
  99
 100   int oflags = O_WRONLY | O_CREAT;
 101 #ifdef O_CLOEXEC
 102   oflags |= O_CLOEXEC;
 103 #endif
 104   lock_fd = __open (PWD_LOCKFILE, oflags, 0600);
 105   if (lock_fd == -1)
 106     /* Cannot create lock file.  */
 107     RETURN_CLOSE_FD (-1);
 108
 109 #ifndef __ASSUME_O_CLOEXEC
 110 # ifdef O_CLOEXEC
 111   if (__have_o_cloexec <= 0)
 112 # endif
 113     {
 114       /* Make sure file gets correctly closed when process finished.  */
 115       int flags = __fcntl (lock_fd, F_GETFD, 0);
 116       if (flags == -1)
 117         /* Cannot get file flags.  */
 118         RETURN_CLOSE_FD (-1);
 119 # ifdef O_CLOEXEC
 120       if (__have_o_cloexec == 0)
 121         __have_o_cloexec = (flags & FD_CLOEXEC) == 0 ? -1 : 1;
 122       if (__have_o_cloexec < 0)
 123 # endif
 124         {
 125           flags |= FD_CLOEXEC;          /* Close on exit.  */
 126           if (__fcntl (lock_fd, F_SETFD, flags) < 0)
 127             /* Cannot set new flags.  */
 128             RETURN_CLOSE_FD (-1);
 129         }
 130     }
 131 #endif
 132
 133   /* Now we have to get exclusive write access.  Since multiple
 134      process could try this we won't stop when it first fails.
 135      Instead we set a timeout for the system call.  Once the timer
 136      expires it is likely that there are some problems which cannot be
 137      resolved by waiting.
 138
 139      It is important that we don't change the signal state.  We must
 140      restore the old signal behaviour.  */
 141   memset (&new_act, '\0', sizeof (struct sigaction));
 142   new_act.sa_handler = noop_handler;
 143   __sigfillset (&new_act.sa_mask);
 144   new_act.sa_flags = 0ul;
 145
 146   /* Install new action handler for alarm and save old.  */
 147   if (__sigaction (SIGALRM, &new_act, &saved_act) < 0)
 148     /* Cannot install signal handler.  */
 149     RETURN_CLOSE_FD (-1);
 150
 151   /* Now make sure the alarm signal is not blocked.  */
 152   __sigemptyset (&new_set);
 153   __sigaddset (&new_set, SIGALRM);
 154   if (__sigprocmask (SIG_UNBLOCK, &new_set, &saved_set) < 0)
 155     RETURN_RESTORE_HANDLER (-1);
 156
 157   /* Start timer.  If we cannot get the lock in the specified time we
 158      get a signal.  */
 159   alarm (TIMEOUT);
 160
 161   /* Try to get the lock.  */
 162   memset (&fl, '\0', sizeof (struct flock));
 163   fl.l_type = F_WRLCK;
 164   fl.l_whence = SEEK_SET;
 165   result = __fcntl (lock_fd, F_SETLKW, &fl);
 166
 167   RETURN_CLEAR_ALARM (result);
 168 }
 169 weak_alias (__lckpwdf, lckpwdf)
 170
 171
 172 int
 173 __ulckpwdf (void)
 174 {
 175   int result;
 176
 177   if (lock_fd == -1)
 178     /* There is no lock set.  */
 179     result = -1;
 180   else
 181     {
 182       /* Prevent problems caused by multiple threads.  */
 183       __libc_lock_lock (lock);
 184
 185       result = __close (lock_fd);
 186
 187       /* Mark descriptor as unused.  */
 188       lock_fd = -1;
 189
 190       /* Clear mutex.  */
 191       __libc_lock_unlock (lock);
 192     }
 193
 194   return result;
 195 }
 196 weak_alias (__ulckpwdf, ulckpwdf)
 197
 198
 199 static void
 200 noop_handler (int sig)
 201 {
 202   /* We simply return which makes the `fcntl' call return with an error.  */
 203 }