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Diffstat (limited to '')
-rw-r--r-- | lib/group-member.c | 114 |
1 files changed, 114 insertions, 0 deletions
diff --git a/lib/group-member.c b/lib/group-member.c new file mode 100644 index 0000000..96a09f9 --- /dev/null +++ b/lib/group-member.c @@ -0,0 +1,114 @@ +/* group-member.c -- determine whether group id is in calling user's group list + + Copyright (C) 1994, 1997-1998, 2003, 2005-2006, 2009-2023 Free Software + Foundation, Inc. + + This file is free software: you can redistribute it and/or modify + it under the terms of the GNU Lesser General Public License as + published by the Free Software Foundation; either version 2.1 of the + License, or (at your option) any later version. + + This file is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public License + along with this program. If not, see <https://www.gnu.org/licenses/>. */ + +#include <config.h> + +/* Specification. */ +#include <unistd.h> + +#include <stdckdint.h> +#include <stdio.h> +#include <sys/types.h> +#include <stdlib.h> + +/* Most processes have no more than this many groups, and for these + processes we can avoid using malloc. */ +enum { GROUPBUF_SIZE = 100 }; + +struct group_info + { + gid_t *group; + gid_t groupbuf[GROUPBUF_SIZE]; + }; + +static void +free_group_info (struct group_info const *g) +{ + if (g->group != g->groupbuf) + free (g->group); +} + +static int +get_group_info (struct group_info *gi) +{ + int n_groups = getgroups (GROUPBUF_SIZE, gi->groupbuf); + gi->group = gi->groupbuf; + + if (n_groups < 0) + { + int n_group_slots = getgroups (0, NULL); + size_t nbytes; + if (! ckd_mul (&nbytes, n_group_slots, sizeof *gi->group)) + { + gi->group = malloc (nbytes); + if (gi->group) + n_groups = getgroups (n_group_slots, gi->group); + } + } + + /* In case of error, the user loses. */ + return n_groups; +} + +/* Return non-zero if GID is one that we have in our groups list. + Note that the groups list is not guaranteed to contain the current + or effective group ID, so they should generally be checked + separately. */ + +int +group_member (gid_t gid) +{ + int i; + int found; + struct group_info gi; + int n_groups = get_group_info (&gi); + + /* Search through the list looking for GID. */ + found = 0; + for (i = 0; i < n_groups; i++) + { + if (gid == gi.group[i]) + { + found = 1; + break; + } + } + + free_group_info (&gi); + + return found; +} + +#ifdef TEST + +int +main (int argc, char **argv) +{ + int i; + + for (i = 1; i < argc; i++) + { + gid_t gid; + + gid = atoi (argv[i]); + printf ("%d: %s\n", gid, group_member (gid) ? "yes" : "no"); + } + exit (0); +} + +#endif /* TEST */ |