coreutils/lib/group-member.c

/* group-member.c -- determine whether group id is in calling user's group list
   Copyright (C) 1994, 1997, 1998, 2003, 2005 Free Software Foundation, Inc.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2, or (at your option)
   any later version.

   This program 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 General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software Foundation,
   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */

#ifdef HAVE_CONFIG_H
# include <config.h>
#endif

#include "group-member.h"

#include <stdbool.h>
#include <stdio.h>
#include <sys/types.h>
#include <stdlib.h>

#include <unistd.h>

#include "xalloc.h"

struct group_info
  {
    int n_groups;
    GETGROUPS_T *group;
  };

#if HAVE_GETGROUPS

static void
free_group_info (struct group_info const *g)
{
  free (g->group);
}

static bool
get_group_info (struct group_info *gi)
{
  int n_groups;
  int n_group_slots = getgroups (0, NULL);
  GETGROUPS_T *group;

  if (n_group_slots < 0)
    return false;

  /* Avoid xnmalloc, as it goes awry when SIZE_MAX < n_group_slots.  */
  if (xalloc_oversized (n_group_slots, sizeof *group))
    xalloc_die ();
  group = xmalloc (n_group_slots * sizeof *group);
  n_groups = getgroups (n_group_slots, group);

  /* In case of error, the user loses. */
  if (n_groups < 0)
    {
      free (group);
      return false;
    }

  gi->n_groups = n_groups;
  gi->group = group;

  return true;
}

#endif /* not HAVE_GETGROUPS */

/* Return non-zero if GID is one that we have in our groups list.
   If there is no getgroups function, return non-zero if GID matches
   either of the current or effective group IDs.  */

int
group_member (gid_t gid)
{
#ifndef HAVE_GETGROUPS
  return ((gid == getgid ()) || (gid == getegid ()));
#else
  int i;
  int found;
  struct group_info gi;

  if (! get_group_info (&gi))
    return 0;

  /* Search through the list looking for GID. */
  found = 0;
  for (i = 0; i < gi.n_groups; i++)
    {
      if (gid == gi.group[i])
	{
	  found = 1;
	  break;
	}
    }

  free_group_info (&gi);

  return found;
#endif /* HAVE_GETGROUPS */
}

#ifdef TEST

char *program_name;

int
main (int argc, char **argv)
{
  int i;

  program_name = argv[0];

  for (i=1; i<argc; i++)
    {
      gid_t gid;

      gid = atoi (argv[i]);
      printf ("%d: %s\n", gid, group_member (gid) ? "yes" : "no");
    }
  exit (0);
}

#endif /* TEST */