1/* group-member.c -- determine whether group id is in calling user's group list
2
3   Copyright (C) 1994, 1997-1998, 2003, 2005-2006, 2009-2010 Free Software
4   Foundation, Inc.
5
6   This program is free software: you can redistribute it and/or modify
7   it under the terms of the GNU General Public License as published by
8   the Free Software Foundation; either version 3 of the License, or
9   (at your option) any later version.
10
11   This program 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
14   GNU General Public License for more details.
15
16   You should have received a copy of the GNU General Public License
17   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
18
19#include <config.h>
20
21#include "group-member.h"
22
23#include <stdbool.h>
24#include <stdio.h>
25#include <sys/types.h>
26#include <stdlib.h>
27
28#include <unistd.h>
29
30#include "xalloc.h"
31
32struct group_info
33  {
34    int n_groups;
35    gid_t *group;
36  };
37
38static void
39free_group_info (struct group_info const *g)
40{
41  free (g->group);
42}
43
44static bool
45get_group_info (struct group_info *gi)
46{
47  int n_groups;
48  int n_group_slots = getgroups (0, NULL);
49  gid_t *group;
50
51  if (n_group_slots < 0)
52    return false;
53
54  /* Avoid xnmalloc, as it goes awry when SIZE_MAX < n_group_slots.  */
55  if (xalloc_oversized (n_group_slots, sizeof *group))
56    xalloc_die ();
57  group = xmalloc (n_group_slots * sizeof *group);
58  n_groups = getgroups (n_group_slots, group);
59
60  /* In case of error, the user loses. */
61  if (n_groups < 0)
62    {
63      free (group);
64      return false;
65    }
66
67  gi->n_groups = n_groups;
68  gi->group = group;
69
70  return true;
71}
72
73/* Return non-zero if GID is one that we have in our groups list.
74   Note that the groups list is not guaranteed to contain the current
75   or effective group ID, so they should generally be checked
76   separately.  */
77
78int
79group_member (gid_t gid)
80{
81  int i;
82  int found;
83  struct group_info gi;
84
85  if (! get_group_info (&gi))
86    return 0;
87
88  /* Search through the list looking for GID. */
89  found = 0;
90  for (i = 0; i < gi.n_groups; i++)
91    {
92      if (gid == gi.group[i])
93        {
94          found = 1;
95          break;
96        }
97    }
98
99  free_group_info (&gi);
100
101  return found;
102}
103
104#ifdef TEST
105
106char *program_name;
107
108int
109main (int argc, char **argv)
110{
111  int i;
112
113  program_name = argv[0];
114
115  for (i = 1; i < argc; i++)
116    {
117      gid_t gid;
118
119      gid = atoi (argv[i]);
120      printf ("%d: %s\n", gid, group_member (gid) ? "yes" : "no");
121    }
122  exit (0);
123}
124
125#endif /* TEST */
126