| 1 | /* group-member.c -- determine whether group id is in calling user's group list |
| 2 | |
| 3 | Copyright (C) 1994, 1997-1998, 2003, 2005-2006, 2009-2013 Free Software |
| 4 | Foundation, Inc. |
| 5 | |
| 6 | This program is free software: you can redistribute it and/or modify |
| 7 | it under the terms of the GNU General Public License as published by |
| 8 | the Free Software Foundation; either version 3 of the License, or |
| 9 | (at your option) any later version. |
| 10 | |
| 11 | This program is distributed in the hope that it will be useful, |
| 12 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 13 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 14 | GNU General Public License for more details. |
| 15 | |
| 16 | You should have received a copy of the GNU General Public License |
| 17 | along with this program. If not, see <http://www.gnu.org/licenses/>. */ |
| 18 | |
| 19 | #include <config.h> |
| 20 | |
| 21 | /* Specification. */ |
| 22 | #include <unistd.h> |
| 23 | |
| 24 | #include <stdio.h> |
| 25 | #include <sys/types.h> |
| 26 | #include <stdlib.h> |
| 27 | |
| 28 | #include "xalloc-oversized.h" |
| 29 | |
| 30 | /* Most processes have no more than this many groups, and for these |
| 31 | processes we can avoid using malloc. */ |
| 32 | enum { GROUPBUF_SIZE = 100 }; |
| 33 | |
| 34 | struct group_info |
| 35 | { |
| 36 | gid_t *group; |
| 37 | gid_t groupbuf[GROUPBUF_SIZE]; |
| 38 | }; |
| 39 | |
| 40 | static void |
| 41 | free_group_info (struct group_info const *g) |
| 42 | { |
| 43 | if (g->group != g->groupbuf) |
| 44 | free (g->group); |
| 45 | } |
| 46 | |
| 47 | static int |
| 48 | get_group_info (struct group_info *gi) |
| 49 | { |
| 50 | int n_groups = getgroups (GROUPBUF_SIZE, gi->groupbuf); |
| 51 | gi->group = gi->groupbuf; |
| 52 | |
| 53 | if (n_groups < 0) |
| 54 | { |
| 55 | int n_group_slots = getgroups (0, NULL); |
| 56 | if (0 <= n_group_slots |
| 57 | && ! xalloc_oversized (n_group_slots, sizeof *gi->group)) |
| 58 | { |
| 59 | gi->group = malloc (n_group_slots * sizeof *gi->group); |
| 60 | if (gi->group) |
| 61 | n_groups = getgroups (n_group_slots, gi->group); |
| 62 | } |
| 63 | } |
| 64 | |
| 65 | /* In case of error, the user loses. */ |
| 66 | return n_groups; |
| 67 | } |
| 68 | |
| 69 | /* Return non-zero if GID is one that we have in our groups list. |
| 70 | Note that the groups list is not guaranteed to contain the current |
| 71 | or effective group ID, so they should generally be checked |
| 72 | separately. */ |
| 73 | |
| 74 | int |
| 75 | group_member (gid_t gid) |
| 76 | { |
| 77 | int i; |
| 78 | int found; |
| 79 | struct group_info gi; |
| 80 | int n_groups = get_group_info (&gi); |
| 81 | |
| 82 | /* Search through the list looking for GID. */ |
| 83 | found = 0; |
| 84 | for (i = 0; i < n_groups; i++) |
| 85 | { |
| 86 | if (gid == gi.group[i]) |
| 87 | { |
| 88 | found = 1; |
| 89 | break; |
| 90 | } |
| 91 | } |
| 92 | |
| 93 | free_group_info (&gi); |
| 94 | |
| 95 | return found; |
| 96 | } |
| 97 | |
| 98 | #ifdef TEST |
| 99 | |
| 100 | char *program_name; |
| 101 | |
| 102 | int |
| 103 | main (int argc, char **argv) |
| 104 | { |
| 105 | int i; |
| 106 | |
| 107 | program_name = argv[0]; |
| 108 | |
| 109 | for (i = 1; i < argc; i++) |
| 110 | { |
| 111 | gid_t gid; |
| 112 | |
| 113 | gid = atoi (argv[i]); |
| 114 | printf ("%d: %s\n", gid, group_member (gid) ? "yes" : "no"); |
| 115 | } |
| 116 | exit (0); |
| 117 | } |
| 118 | |
| 119 | #endif /* TEST */ |