1 /* mgetgroups.c -- return a list of the groups a user or current process is in
3 Copyright (C) 2007-2009 Free Software Foundation, Inc.
5 This program is free software: you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation, either version 3 of the License, or
8 (at your option) any later version.
10 This program 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
13 GNU General Public License for more details.
15 You should have received a copy of the GNU General Public License
16 along with this program. If not, see <http://www.gnu.org/licenses/>. */
18 /* Extracted from coreutils' src/id.c. */
22 #include "mgetgroups.h"
33 #include "getugroups.h"
37 realloc_groupbuf (gid_t *g, size_t num)
39 if (xalloc_oversized (num, sizeof *g))
45 return realloc (g, num * sizeof *g);
48 /* Like getugroups, but store the result in malloc'd storage.
49 Set *GROUPS to the malloc'd list of all group IDs of which USERNAME
50 is a member. If GID is not -1, store it first. GID should be the
51 group ID (pw_gid) obtained from getpwuid, in case USERNAME is not
52 listed in the groups database (e.g., /etc/groups). If USERNAME is
53 NULL, store the supplementary groups of the current process, and GID
54 should be -1 or the effective group ID (getegid). Upon failure,
55 don't modify *GROUPS, set errno, and return -1. Otherwise, return
56 the number of groups. */
59 mgetgroups (char const *username, gid_t gid, gid_t **groups)
66 /* We prefer to use getgrouplist if available, because it has better
67 performance characteristics.
69 In glibc 2.3.2, getgrouplist is buggy. If you pass a zero as the
70 length of the output buffer, getgrouplist will still write to the
71 buffer. Contrary to what some versions of the getgrouplist
72 manpage say, this doesn't happen with nonzero buffer sizes.
73 Therefore our usage here just avoids a zero sized buffer. */
76 enum { N_GROUPS_INIT = 10 };
77 max_n_groups = N_GROUPS_INIT;
79 g = realloc_groupbuf (NULL, max_n_groups);
86 int last_n_groups = max_n_groups;
88 /* getgrouplist updates max_n_groups to num required. */
89 ng = getgrouplist (username, gid, g, &max_n_groups);
91 /* Some systems (like Darwin) have a bug where they
92 never increase max_n_groups. */
93 if (ng < 0 && last_n_groups == max_n_groups)
96 if ((h = realloc_groupbuf (g, max_n_groups)) == NULL)
98 int saved_errno = errno;
108 /* On success some systems just return 0 from getgrouplist,
109 so return max_n_groups rather than ng. */
114 /* else no username, so fall through and use getgroups. */
117 max_n_groups = (username
118 ? getugroups (0, NULL, username, gid)
119 : getgroups (0, NULL) + (gid != (gid_t) -1));
121 /* If we failed to count groups with NULL for a buffer,
122 try again with a non-NULL one, just in case. */
123 if (max_n_groups < 0)
126 g = realloc_groupbuf (NULL, max_n_groups);
131 ? getugroups (max_n_groups, g, username, gid)
132 : getgroups (max_n_groups, g + (gid != (gid_t) -1)));
136 int saved_errno = errno;
142 if (!username && gid != (gid_t) -1)