summaryrefslogtreecommitdiff
path: root/login/pututline_r.c
blob: 382716ce804f2bf985d73ff2b9abff36142d569e (plain)
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
124
125
126
127
128
129
130
131
132
133
134
/* 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>
#include <sys/stat.h>


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

int
pututline_r (const struct utmp *id, 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->loc_utmp >= sizeof (struct utmp)
      && utmp_data->ubuf.ut_type != id->ut_type)
    {
      /* We must not overwrite the data in UTMP_DATA.  */
      struct utmp_data *data_tmp = alloca (sizeof (*data_tmp));
      struct utmp *dummy;

      *data_tmp = *utmp_data;
      utmp_data = data_tmp;

      if (getutid_r (id, &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

  /* 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);
    }

  /* Find out how large the file is.  */
  result = fstat (utmp_data->ut_fd, &st);

  if (result == 0)
    /* Position file correctly.  */
    if (utmp_data->loc_utmp < sizeof (struct utmp))
      /* Not located at any valid entry.  Add at the end.  */
      {
	result = lseek (utmp_data->ut_fd, 0L, SEEK_END);
	if (result == 0)
	  /* Where we'll be if the write succeeds.  */
	  utmp_data->loc_utmp = st.st_size + sizeof (struct utmp);
      }
    else if (utmp_data->loc_utmp <= st.st_size)
      result =
	lseek (utmp_data->ut_fd, utmp_data->loc_utmp - sizeof (struct utmp),
	       SEEK_SET);

  if (result == 0)
    /* Write the new data.  */
    if (write (utmp_data->ut_fd, id, 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;
}