1 /*
2  * Copyright (c) 2004, 2005 Darren Tucker (dtucker at zip com au).
3  *
4  * Permission to use, copy, modify, and distribute this software for any
5  * purpose with or without fee is hereby granted, provided that the above
6  * copyright notice and this permission notice appear in all copies.
7  *
8  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
9  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
10  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
11  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
12  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
13  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
14  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
15  */
16 
17 #include <sys/types.h>
18 
19 #include <errno.h>
20 #include <unistd.h>
21 
22 int
23 setresuid(uid_t ruid, uid_t euid, uid_t suid)
24 {
25 	uid_t ouid;
26 	int ret = -1;
27 
28 	/* Allow only the tested configuration. */
29 
30 	if (ruid != euid || euid != suid) {
31 		errno = ENOSYS;
32 		return -1;
33 	}
34 	ouid = getuid();
35 
36 	if ((ret = setreuid(euid, euid)) == -1)
37 		return -1;
38 
39 	/*
40 	 * When real, effective and saved uids are the same and we have
41 	 * changed uids, sanity check that we cannot restore the old uid.
42 	 */
43 
44 	if (ruid == euid && euid == suid && ouid != ruid &&
45 	    setuid(ouid) != -1 && seteuid(ouid) != -1) {
46 		errno = EINVAL;
47 		return -1;
48 	}
49 
50 	/*
51 	 * Finally, check that the real and effective uids are what we
52 	 * expect.
53 	 */
54 	if (getuid() != ruid || geteuid() != euid) {
55 		errno = EACCES;
56 		return -1;
57 	}
58 
59 	return ret;
60 }