lib/group-member.c

   1 /* group-member.c -- determine whether group id is in calling user's group list
   2    Copyright (C) 1994, 1997, 1998 Free Software Foundation, Inc.
   3
   4    This program is free software; you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation; either version 2, or (at your option)
   7    any later version.
   8
   9    This program is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program; if not, write to the Free Software Foundation,
  16    Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
  17
  18 #if HAVE_CONFIG_H
  19 # include <config.h>
  20 #endif
  21
  22 #include <stdio.h>
  23 #include <sys/types.h>
  24
  25 #ifdef STDC_HEADERS
  26 # include <stdlib.h>
  27 #endif
  28
  29 #if HAVE_UNISTD_H
  30 # include <unistd.h>
  31 #endif
  32
  33 #include "group-member.h"
  34 #include "xalloc.h"
  35
  36 struct group_info
  37   {
  38     int n_groups;
  39     GETGROUPS_T *group;
  40   };
  41
  42 #if HAVE_GETGROUPS
  43
  44 static void
  45 free_group_info (struct group_info *g)
  46 {
  47   free (g->group);
  48   free (g);
  49 }
  50
  51 static struct group_info *
  52 get_group_info (void)
  53 {
  54   int n_groups;
  55   int n_group_slots;
  56   struct group_info *gi;
  57   GETGROUPS_T *group;
  58
  59   /* getgroups () returns the number of elements that it was able to
  60      place into the array.  We simply continue to call getgroups ()
  61      until the number of elements placed into the array is smaller than
  62      the physical size of the array. */
  63
  64   group = NULL;
  65   n_groups = 0;
  66   n_group_slots = 0;
  67   while (n_groups == n_group_slots)
  68     {
  69       n_group_slots += 64;
  70       group = (GETGROUPS_T *) xrealloc (group,
  71                                         n_group_slots * sizeof (GETGROUPS_T));
  72       n_groups = getgroups (n_group_slots, group);
  73     }
  74
  75   /* In case of error, the user loses. */
  76   if (n_groups < 0)
  77     {
  78       free (group);
  79       return NULL;
  80     }
  81
  82   gi = (struct group_info *) xmalloc (sizeof (*gi));
  83   gi->n_groups = n_groups;
  84   gi->group = group;
  85
  86   return gi;
  87 }
  88
  89 #endif /* not HAVE_GETGROUPS */
  90
  91 /* Return non-zero if GID is one that we have in our groups list.
  92    If there is no getgroups function, return non-zero if GID matches
  93    either of the current or effective group IDs.  */
  94
  95 int
  96 group_member (gid_t gid)
  97 {
  98 #ifndef HAVE_GETGROUPS
  99   return ((gid == getgid ()) || (gid == getegid ()));
 100 #else
 101   int i;
 102   int found;
 103   struct group_info *gi;
 104
 105   gi = get_group_info ();
 106   if (gi == NULL)
 107     return 0;
 108
 109   /* Search through the list looking for GID. */
 110   found = 0;
 111   for (i = 0; i < gi->n_groups; i++)
 112     {
 113       if (gid == gi->group[i])
 114         {
 115           found = 1;
 116           break;
 117         }
 118     }
 119
 120   free_group_info (gi);
 121
 122   return found;
 123 #endif /* HAVE_GETGROUPS */
 124 }
 125
 126 #ifdef TEST
 127
 128 char *program_name;
 129
 130 int
 131 main (int argc, char** argv)
 132 {
 133   int i;
 134
 135   program_name = argv[0];
 136
 137   for (i=1; i<argc; i++)
 138     {
 139       gid_t gid;
 140
 141       gid = atoi (argv[i]);
 142       printf ("%d: %s\n", gid, group_member (gid) ? "yes" : "no");
 143     }
 144   exit (0);
 145 }
 146
 147 #endif /* TEST */