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)