1 /*
2 * Utility routines.
3 *
4 * Copyright (C) 2017 Denys Vlasenko
5 *
6 * Licensed under GPLv2, see file LICENSE in this source tree.
7 */
8
9 //kbuild:lib-y += bb_getgroups.o
10
11 #include "libbb.h"
12
bb_getgroups(int * ngroups,gid_t * group_array)13 gid_t* FAST_FUNC bb_getgroups(int *ngroups, gid_t *group_array)
14 {
15 int n = ngroups ? *ngroups : 0;
16
17 /* getgroups may be a bit expensive, try to use it only once */
18 if (n < 32)
19 n = 32;
20
21 for (;;) {
22 // FIXME: ash tries so hard to not die on OOM (when we are called from test),
23 // and we spoil it with just one xrealloc here
24 group_array = xrealloc(group_array, (n+1) * sizeof(group_array[0]));
25 n = getgroups(n, group_array);
26 /*
27 * If buffer is too small, kernel does not return new_n > n.
28 * It returns -1 and EINVAL:
29 */
30 if (n >= 0) {
31 /* Terminator for bb_getgroups(NULL, NULL) usage */
32 group_array[n] = (gid_t) -1;
33 break;
34 }
35 if (errno == EINVAL) { /* too small? */
36 /* This is the way to ask kernel how big the array is */
37 n = getgroups(0, group_array);
38 continue;
39 }
40 /* Some other error (should never happen on Linux) */
41 bb_simple_perror_msg_and_die("getgroups");
42 }
43
44 if (ngroups)
45 *ngroups = n;
46 return group_array;
47 }
48