glibc/posix/group_member.c

/* `group_member' -- test if process is in a given group.
   Copyright (C) 1995-2017 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library 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
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <http://www.gnu.org/licenses/>.  */

#include <sys/types.h>
#include <unistd.h>
#include <stdlib.h>
#include <limits.h>

#ifndef NGROUPS_MAX
#define NGROUPS_MAX	16	/* First guess.  */
#endif

int
__group_member (gid_t gid)
{
  int n, size;
  gid_t *groups;

  size = NGROUPS_MAX;
  do
    {
      groups = __alloca (size * sizeof *groups);
      n = __getgroups (size, groups);
      size *= 2;
    }
  while (n == size / 2);

  while (n-- > 0)
    if (groups[n] == gid)
      return 1;

  return 0;
}
weak_alias (__group_member, group_member)