posix/group_member.c

   1 /* `group_member' -- test if process is in a given group.
   2    Copyright (C) 1995-2023 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <sys/types.h>
  20 #include <unistd.h>
  21 #include <stdlib.h>
  22 #include <limits.h>
  23
  24 #ifndef NGROUPS_MAX
  25 #define NGROUPS_MAX     16      /* First guess.  */
  26 #endif
  27
  28 int
  29 __group_member (gid_t gid)
  30 {
  31   int n, size;
  32   gid_t *groups;
  33
  34   size = NGROUPS_MAX;
  35   do
  36     {
  37       groups = __alloca (size * sizeof *groups);
  38       n = __getgroups (size, groups);
  39       size *= 2;
  40     }
  41   while (n == size / 2);
  42
  43   while (n-- > 0)
  44     if (groups[n] == gid)
  45       return 1;
  46
  47   return 0;
  48 }
  49 weak_alias (__group_member, group_member)