/*-
 * Copyright (c) 2017 Taylor R. Campbell
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/* No _POSIX_C_SOURCE -- setgroups is a non-POSIX extension.  */

#include "onion_setuidgid.h"

#ifdef __linux__
#include <grp.h>
#endif
#include <unistd.h>

/*
 * onion_setuidgid(uid, gid)
 *
 *	If not -1, set the process's uid, primary gid, and sole
 *	secondary gid, in the appropriate order, to drop privileges.
 */
int
onion_setuidgid(uid_t uid, gid_t gid)
{

	/*
	 * First set secondary groups and primary GID, while we are
	 * still UID-privileged.
	 */
	if (gid != (gid_t)-1) {
		if (setgroups(1, &gid) == -1)
			return -1;
		if (setgid(gid) == -1)
			return -1;
	}

	/* Then drop UID privileges.  */
	if (uid != (uid_t)-1) {
		if (setuid(uid) == -1)
			return -1;
	}

	/* Success!  */
	return 0;
}