about summary refs log tree commit diff
path: root/login/pututline_r.c
blob: 07322e57404dadd0ed0b55b52884db1524b52c23 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
/* Copyright (C) 1996 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Ulrich Drepper <drepper@cygnus.com>, 1996.

The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Library General Public License as
published by the Free Software Foundation; either version 2 of the
License, or (at your option) any later version.

The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
Library General Public License for more details.

You should have received a copy of the GNU Library General Public
License along with the GNU C Library; see the file COPYING.LIB.  If
not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.  */

#include <alloca.h>
#include <errno.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <utmp.h>
#include <sys/file.h>


/* XXX An alternative solution would be to call a SUID root program
   which write the new value.  */

int
pututline_r (const struct utmp *utmp_ptr, struct utmp_data *utmp_data)
{
  struct stat st;
  int result = 0;

#if _HAVE_UT_TYPE - 0
  /* Test whether ID has any of the legal types because we have to
     prevent illegal entries.  */
  if (id->ut_type != RUN_LVL && id->ut_type != BOOT_TIME
      && id->ut_type != OLD_TIME && id->ut_type != NEW_TIME
      && id->ut_type != INIT_PROCESS && id->ut_type != LOGIN_PROCESS
      && id->ut_type != USER_PROCESS && id->ut_type != DEAD_PROCESS)
    /* No, using '<' and '>' for the test is not possible.  */
    {
      errno = EINVAL;
      return -1;
    }
#endif

  /* Open utmp file if not already done.  */
  if (utmp_data->ut_fd == -1)
    {
      setutent_r (utmp_data);
      if (utmp_data->ut_fd == -1)
	return -1;
    }

#if _HAVE_UT_TYPE - 0
  /* Seek position to write.  */
  if (utmp_data->ubuf.ut_type != utmp_ptr->ut_type)
    {
      /* We must not overwrite the data in UTMP_DATA.  */
      struct utmp_data *data_tmp = alloca (sizeof (utmp_data));
      struct utmp *dummy;
      off_t new_pos;

      *data_tmp = *utmp_data;
      utmp_data = data_tmp;

      if (getutid_r (utmp_ptr, &dummy, utmp_data) < 0)
	{
	  if (errno != ESRCH)
	    /* Some error occured.  If no entry was found, the position
	       pointer now is at the end of the file.  */
	    return -1;

	  /* Set position pointer to position after adding of the record.  */
	  utmp_data->loc_utmp += sizeof (struct utmp);
    }
#endif

  /* Find out how large the file is.  */
  if (fstat (utmp_data->ut_fd, &st) < 0)
    return -1;

  /* Position file correctly.  */
  if (utmp_data->loc_utmp <= st.st_size
      && lseek (utmp_data->ut_fd, utmp_data->loc_utmp - sizeof (struct utmp),
		SEEK_SET) < 0)
    return -1;

  /* Try to lock the file.  */
  if (flock (utmp_data->ut_fd, LOCK_EX | LOCK_NB) < 0 && errno != ENOSYS)
    {
      /* Oh, oh.  The file is already locked.  Wait a bit and try again.  */
      sleep (1);

      /* This time we ignore the error.  */
      (void) flock (utmp_data->ut_fd, LOCK_EX | LOCK_NB);
    }

  /* Write the new data.  */
  if (write (utmp_data->ut_fd, utmp_ptr, sizeof (struct utmp))
      != sizeof (struct utmp))
    {
      /* If we appended a new record this is only partially written.
	 Remove it.  */
      if (utmp_data->loc_utmp > st.st_size)
	{
	  (void) ftruncate (utmp_data->ut_fd, st.st_size);
	  utmp_data->loc_utmp = st.st_size;
	}

      result = -1;
    }

  /* And unlock the file.  */
  (void) flock (utmp_data->ut_fd, LOCK_UN);

  return result;
}