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
  35 char *xmalloc ();
  36 char *xrealloc ();
  37
  38 struct group_info
  39   {
  40     int n_groups;
  41     GETGROUPS_T *group;
  42   };
  43
  44 #if HAVE_GETGROUPS
  45
  46 static void
  47 free_group_info (struct group_info *g)
  48 {
  49   free (g->group);
  50   free (g);
  51 }
  52
  53 static struct group_info *
  54 get_group_info (void)
  55 {
  56   int n_groups;
  57   int n_group_slots;
  58   struct group_info *gi;
  59   GETGROUPS_T *group;
  60
  61   /* getgroups () returns the number of elements that it was able to
  62      place into the array.  We simply continue to call getgroups ()
  63      until the number of elements placed into the array is smaller than
  64      the physical size of the array. */
  65
  66   group = NULL;
  67   n_groups = 0;
  68   n_group_slots = 0;
  69   while (n_groups == n_group_slots)
  70     {
  71       n_group_slots += 64;
  72       group = (GETGROUPS_T *) xrealloc (group,
  73                                         n_group_slots * sizeof (GETGROUPS_T));
  74       n_groups = getgroups (n_group_slots, group);
  75     }
  76
  77   /* In case of error, the user loses. */
  78   if (n_groups < 0)
  79     {
  80       free (group);
  81       return NULL;
  82     }
  83
  84   gi = (struct group_info *) xmalloc (sizeof (*gi));
  85   gi->n_groups = n_groups;
  86   gi->group = group;
  87
  88   return gi;
  89 }
  90
  91 #endif /* not HAVE_GETGROUPS */
  92
  93 /* Return non-zero if GID is one that we have in our groups list.
  94    If there is no getgroups function, return non-zero if GID matches
  95    either of the current or effective group IDs.  */
  96
  97 int
  98 group_member (gid_t gid)
  99 {
 100 #ifndef HAVE_GETGROUPS
 101   return ((gid == getgid ()) || (gid == getegid ()));
 102 #else
 103   int i;
 104   int found;
 105   struct group_info *gi;
 106
 107   gi = get_group_info ();
 108   if (gi == NULL)
 109     return 0;
 110
 111   /* Search through the list looking for GID. */
 112   found = 0;
 113   for (i = 0; i < gi->n_groups; i++)
 114     {
 115       if (gid == gi->group[i])
 116         {
 117           found = 1;
 118           break;
 119         }
 120     }
 121
 122   free_group_info (gi);
 123
 124   return found;
 125 #endif /* HAVE_GETGROUPS */
 126 }
 127
 128 #ifdef TEST
 129
 130 char *program_name;
 131
 132 int
 133 main (int argc, char** argv)
 134 {
 135   int i;
 136
 137   program_name = argv[0];
 138
 139   for (i=1; i<argc; i++)
 140     {
 141       gid_t gid;
 142
 143       gid = atoi (argv[i]);
 144       printf ("%d: %s\n", gid, group_member (gid) ? "yes" : "no");
 145     }
 146   exit (0);
 147 }
 148
 149 #endif /* TEST */