/* group-member.c -- determine whether group id is in calling user's group list

   Copyright (C) 1994, 1997-1998, 2003, 2005-2006, 2009-2016 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 3 of the License, 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, see <http://www.gnu.org/licenses/>.  */

#include <config.h>

/* Specification.  */

#include <unistd.h>

#include <stdio.h>

#include <sys/types.h>

#include <stdlib.h>

#include "xalloc-oversized.h"

/* Most processes have no more than this many groups, and for these

   processes we can avoid using malloc.  */

enum { GROUPBUF_SIZE = 100 };

struct group_info

  {

    gid_t *group;

    gid_t groupbuf[GROUPBUF_SIZE];

  };

static void

free_group_info (struct group_info const *g)

{

  if (g->group != g->groupbuf)

    free (g->group);

}

static int

get_group_info (struct group_info *gi)

{

  int n_groups = getgroups (GROUPBUF_SIZE, gi->groupbuf);

  gi->group = gi->groupbuf;

  if (n_groups < 0)

    {

      int n_group_slots = getgroups (0, NULL);

      if (0 <= n_group_slots

          && ! xalloc_oversized (n_group_slots, sizeof *gi->group))

        {

          gi->group = malloc (n_group_slots * sizeof *gi->group);

          if (gi->group)

            n_groups = getgroups (n_group_slots, gi->group);

        }

    }

  /* In case of error, the user loses.  */

  return n_groups;

}

/* Return non-zero if GID is one that we have in our groups list.

   Note that the groups list is not guaranteed to contain the current

   or effective group ID, so they should generally be checked

   separately.  */

int

group_member (gid_t gid)

{

  int i;

  int found;

  struct group_info gi;

  int n_groups = get_group_info (&gi);

  /* Search through the list looking for GID. */

  found = 0;

  for (i = 0; i < n_groups; i++)

    {

      if (gid == gi.group[i])

        {

          found = 1;

          break;

        }

    }

  free_group_info (&gi);

  return found;

}

#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 */