116 lines
2.6 KiB
C
116 lines
2.6 KiB
C
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/* group-member.c -- determine whether group id is in calling user's group list
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Copyright (C) 1994, 1997-1998, 2003, 2005-2006, 2009-2020 Free Software
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Foundation, Inc.
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <https://www.gnu.org/licenses/>. */
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#include <config.h>
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/* Specification. */
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#include <unistd.h>
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#include <stdio.h>
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#include <sys/types.h>
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#include <stdlib.h>
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#include "xalloc-oversized.h"
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/* Most processes have no more than this many groups, and for these
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processes we can avoid using malloc. */
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enum { GROUPBUF_SIZE = 100 };
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struct group_info
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{
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gid_t *group;
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gid_t groupbuf[GROUPBUF_SIZE];
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};
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static void
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free_group_info (struct group_info const *g)
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{
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if (g->group != g->groupbuf)
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free (g->group);
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}
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static int
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get_group_info (struct group_info *gi)
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{
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int n_groups = getgroups (GROUPBUF_SIZE, gi->groupbuf);
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gi->group = gi->groupbuf;
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if (n_groups < 0)
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{
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int n_group_slots = getgroups (0, NULL);
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if (0 <= n_group_slots
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&& ! xalloc_oversized (n_group_slots, sizeof *gi->group))
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{
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gi->group = malloc (n_group_slots * sizeof *gi->group);
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if (gi->group)
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n_groups = getgroups (n_group_slots, gi->group);
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}
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}
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/* In case of error, the user loses. */
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return n_groups;
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}
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/* Return non-zero if GID is one that we have in our groups list.
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Note that the groups list is not guaranteed to contain the current
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or effective group ID, so they should generally be checked
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separately. */
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int
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group_member (gid_t gid)
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{
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int i;
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int found;
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struct group_info gi;
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int n_groups = get_group_info (&gi);
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/* Search through the list looking for GID. */
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found = 0;
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for (i = 0; i < n_groups; i++)
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{
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if (gid == gi.group[i])
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{
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found = 1;
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break;
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}
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}
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free_group_info (&gi);
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return found;
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}
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#ifdef TEST
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int
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main (int argc, char **argv)
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{
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int i;
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for (i = 1; i < argc; i++)
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{
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gid_t gid;
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gid = atoi (argv[i]);
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printf ("%d: %s\n", gid, group_member (gid) ? "yes" : "no");
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}
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exit (0);
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}
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#endif /* TEST */
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