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 "../config.h"
18 
19 #include <sys/types.h>
20 
21 #include <errno.h>
22 #include <unistd.h>
23 
24 int
25 setresuid(uid_t ruid, uid_t euid, uid_t suid)
26 {
27 	uid_t ouid;
28 	int ret = -1;
29 
30 	/* Allow only the tested configuration. */
31 
32 	if (ruid != euid || euid != suid) {
33 		errno = ENOSYS;
34 		return -1;
35 	}
36 	ouid = getuid();
37 
38 	if ((ret = setreuid(euid, euid)) == -1)
39 		return -1;
40 
41 	/*
42 	 * When real, effective and saved uids are the same and we have
43 	 * changed uids, sanity check that we cannot restore the old uid.
44 	 */
45 
46 	if (ruid == euid && euid == suid && ouid != ruid &&
47 	    setuid(ouid) != -1 && seteuid(ouid) != -1) {
48 		errno = EINVAL;
49 		return -1;
50 	}
51 
52 	/*
53 	 * Finally, check that the real and effective uids are what we
54 	 * expect.
55 	 */
56 	if (getuid() != ruid || geteuid() != euid) {
57 		errno = EACCES;
58 		return -1;
59 	}
60 
61 	return ret;
62 }