login/pututline_r.c

   1 /* Copyright (C) 1996 Free Software Foundation, Inc.
   2 This file is part of the GNU C Library.
   3 Contributed by Ulrich Drepper <drepper@cygnus.com>, 1996.
   4
   5 The GNU C Library is free software; you can redistribute it and/or
   6 modify it under the terms of the GNU Library General Public License as
   7 published by the Free Software Foundation; either version 2 of the
   8 License, or (at your option) any later version.
   9
  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 Library General Public License for more details.
  14
  15 You should have received a copy of the GNU Library General Public
  16 License along with the GNU C Library; see the file COPYING.LIB.  If
  17 not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  18 Boston, MA 02111-1307, USA.  */
  19
  20 #include <alloca.h>
  21 #include <errno.h>
  22 #include <stdlib.h>
  23 #include <string.h>
  24 #include <unistd.h>
  25 #include <utmp.h>
  26 #include <sys/file.h>
  27 #include <sys/stat.h>
  28
  29
  30 /* XXX An alternative solution would be to call a SUID root program
  31    which write the new value.  */
  32
  33 int
  34 __pututline_r (const struct utmp *id, struct utmp_data *utmp_data)
  35 {
  36   struct stat st;
  37   int result = 0;
  38
  39 #if _HAVE_UT_TYPE - 0
  40   /* Test whether ID has any of the legal types because we have to
  41      prevent illegal entries.  */
  42   if (id->ut_type != RUN_LVL && id->ut_type != BOOT_TIME
  43       && id->ut_type != OLD_TIME && id->ut_type != NEW_TIME
  44       && id->ut_type != INIT_PROCESS && id->ut_type != LOGIN_PROCESS
  45       && id->ut_type != USER_PROCESS && id->ut_type != DEAD_PROCESS)
  46     /* No, using '<' and '>' for the test is not possible.  */
  47     {
  48       errno = EINVAL;
  49       return -1;
  50     }
  51 #endif
  52
  53   /* Open utmp file if not already done.  */
  54   if (utmp_data->ut_fd == -1)
  55     {
  56       setutent_r (utmp_data);
  57       if (utmp_data->ut_fd == -1)
  58         return -1;
  59     }
  60
  61 #if _HAVE_UT_ID - 0
  62   /* Check whether we need to reposition.  Repositioning is necessary
  63      either if the data in UTMP_DATA is not valid or if the ids don't
  64      match: */
  65   if (id->ut_id[0]
  66       && (utmp_data->loc_utmp < (off_t) sizeof (struct utmp)
  67           || strncmp(utmp_data->ubuf.ut_id, id->ut_id, sizeof (id->ut_id)) != 0))
  68     {
  69       /* We must not overwrite the data in UTMP_DATA since ID may be
  70          aliasing it.  */
  71       struct utmp_data *data_tmp = alloca (sizeof (*data_tmp));
  72       struct utmp *dummy;
  73
  74       *data_tmp = *utmp_data;
  75       utmp_data = data_tmp;
  76
  77       if (getutid_r (id, &dummy, utmp_data) < 0)
  78         {
  79           if (errno != ESRCH)
  80             /* Some error occured.  If no entry was found, the position
  81                pointer now is at the end of the file.  */
  82             return -1;
  83
  84           /* Set position pointer to position behind the record.  */
  85           utmp_data->loc_utmp += sizeof (struct utmp);
  86         }
  87     }
  88 #endif
  89
  90   /* Try to lock the file.  */
  91   if (flock (utmp_data->ut_fd, LOCK_EX | LOCK_NB) < 0 && errno != ENOSYS)
  92     {
  93       /* Oh, oh.  The file is already locked.  Wait a bit and try again.  */
  94       sleep (1);
  95
  96       /* This time we ignore the error.  */
  97       (void) flock (utmp_data->ut_fd, LOCK_EX | LOCK_NB);
  98     }
  99
 100   /* Find out how large the file is.  */
 101   result = fstat (utmp_data->ut_fd, &st);
 102
 103   if (result >= 0)
 104     /* Position file correctly.  */
 105     if (utmp_data->loc_utmp < (off_t) sizeof (struct utmp))
 106       /* Not located at any valid entry.  Add at the end.  */
 107       {
 108         result = lseek (utmp_data->ut_fd, 0L, SEEK_END);
 109         if (result >= 0)
 110           /* Where we'll be if the write succeeds.  */
 111           utmp_data->loc_utmp = st.st_size + sizeof (struct utmp);
 112       }
 113     else if (utmp_data->loc_utmp <= st.st_size)
 114       result =
 115         lseek (utmp_data->ut_fd, utmp_data->loc_utmp - sizeof (struct utmp),
 116                SEEK_SET);
 117
 118   if (result >= 0)
 119     /* Write the new data.  */
 120     if (write (utmp_data->ut_fd, id, sizeof (struct utmp))
 121         != sizeof (struct utmp))
 122       {
 123         /* If we appended a new record this is only partially written.
 124            Remove it.  */
 125         if (utmp_data->loc_utmp > st.st_size)
 126           {
 127             (void) ftruncate (utmp_data->ut_fd, st.st_size);
 128             utmp_data->loc_utmp = st.st_size;
 129           }
 130
 131         result = -1;
 132       }
 133
 134   /* And unlock the file.  */
 135   (void) flock (utmp_data->ut_fd, LOCK_UN);
 136
 137   return result;
 138 }
 139 weak_alias (__pututline_r, pututline_r)