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#define _GNU_SOURCE
#include <grp.h>
#include <limits.h>
#include <stdlib.h>
int initgroups(const char *user, gid_t gid)
{
gid_t buf[32], *groups = buf;
int count = sizeof buf / sizeof *buf, prev_count = count;
while (getgrouplist(user, gid, groups, &count) < 0) {
if (groups != buf) free(groups);
/* Return if failure isn't buffer size */
if (count <= prev_count)
return -1;
/* Always increase by at least 50% to limit to
* logarithmically many retries on TOCTOU races. */
if (count < prev_count + (prev_count>>1))
count = prev_count + (prev_count>>1);
groups = calloc(count, sizeof *groups);
if (!groups) return -1;
prev_count = count;
}
int ret = setgroups(count, groups);
if (groups != buf) free(groups);
return ret;
}
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