lib/group-member.c

   1 /* group-member.c -- determine whether group id is in calling user's group list
   2    Copyright (C) 1994 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
  16    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.  */
  17
  18 #ifdef 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 #ifdef 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 #ifdef HAVE_GETGROUPS
  45
  46 static void
  47 free_group_info (g)
  48      struct group_info *g;
  49 {
  50   free (g->group);
  51   free (g);
  52 }
  53
  54 static struct group_info *
  55 get_group_info ()
  56 {
  57   int n_groups;
  58   int n_group_slots;
  59   struct group_info *gi;
  60   GETGROUPS_T *group;
  61
  62   /* getgroups () returns the number of elements that it was able to
  63      place into the array.  We simply continue to call getgroups ()
  64      until the number of elements placed into the array is smaller than
  65      the physical size of the array. */
  66
  67   group = NULL;
  68   n_groups = 0;
  69   n_group_slots = 0;
  70   while (n_groups == n_group_slots)
  71     {
  72       n_group_slots += 64;
  73       group = (GETGROUPS_T *) xrealloc (group,
  74                                         n_group_slots * sizeof (GETGROUPS_T));
  75       n_groups = getgroups (n_group_slots, group);
  76     }
  77
  78   /* In case of error, the user loses. */
  79   if (n_groups < 0)
  80     {
  81       free (group);
  82       return NULL;
  83     }
  84
  85   gi = (struct group_info *) xmalloc (sizeof (*gi));
  86   gi->n_groups = n_groups;
  87   gi->group = group;
  88
  89   return gi;
  90 }
  91
  92 #endif /* not HAVE_GETGROUPS */
  93
  94 /* Return non-zero if GID is one that we have in our groups list.
  95    If there is no getgroups function, return non-zero if GID matches
  96    either of the current or effective group IDs.  */
  97
  98 int
  99 group_member (gid)
 100      gid_t gid;
 101 {
 102 #ifndef HAVE_GETGROUPS
 103   return ((gid == getgid ()) || (gid == getegid ()));
 104 #else
 105   int i;
 106   int found;
 107   struct group_info *gi;
 108
 109   gi = get_group_info ();
 110   if (gi == NULL)
 111     return 0;
 112
 113   /* Search through the list looking for GID. */
 114   found = 0;
 115   for (i = 0; i < gi->n_groups; i++)
 116     {
 117       if (gid == gi->group[i])
 118         {
 119           found = 1;
 120           break;
 121         }
 122     }
 123
 124   free_group_info (gi);
 125
 126   return found;
 127 #endif /* HAVE_GETGROUPS */
 128 }
 129
 130 #ifdef TEST
 131
 132 char *program_name;
 133
 134 int
 135 main (int argc, char** argv)
 136 {
 137   int i;
 138
 139   program_name = argv[0];
 140
 141   for (i=1; i<argc; i++)
 142     {
 143       gid_t gid;
 144
 145       gid = atoi (argv[i]);
 146       printf ("%d: %s\n", gid, group_member (gid) ? "yes" : "no");
 147     }
 148   exit (0);
 149 }
 150
 151 #endif /* TEST */