1 af3a75b4 2022-12-02 op /*
 2 af3a75b4 2022-12-02 op  * Copyright (c) 2004, 2005 Darren Tucker (dtucker at zip com au).
 3 af3a75b4 2022-12-02 op  *
 4 af3a75b4 2022-12-02 op  * Permission to use, copy, modify, and distribute this software for any
 5 af3a75b4 2022-12-02 op  * purpose with or without fee is hereby granted, provided that the above
 6 af3a75b4 2022-12-02 op  * copyright notice and this permission notice appear in all copies.
 7 af3a75b4 2022-12-02 op  *
 8 af3a75b4 2022-12-02 op  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 9 af3a75b4 2022-12-02 op  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
10 af3a75b4 2022-12-02 op  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
11 af3a75b4 2022-12-02 op  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
12 af3a75b4 2022-12-02 op  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
13 af3a75b4 2022-12-02 op  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
14 af3a75b4 2022-12-02 op  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
15 af3a75b4 2022-12-02 op  */
16 af3a75b4 2022-12-02 op 
17 af3a75b4 2022-12-02 op #include <sys/types.h>
18 af3a75b4 2022-12-02 op 
19 af3a75b4 2022-12-02 op #include <errno.h>
20 af3a75b4 2022-12-02 op #include <unistd.h>
21 af3a75b4 2022-12-02 op 
22 af3a75b4 2022-12-02 op int
23 af3a75b4 2022-12-02 op setresuid(uid_t ruid, uid_t euid, uid_t suid)
24 af3a75b4 2022-12-02 op {
25 af3a75b4 2022-12-02 op 	uid_t ouid;
26 af3a75b4 2022-12-02 op 	int ret = -1;
27 af3a75b4 2022-12-02 op 
28 af3a75b4 2022-12-02 op 	/* Allow only the tested configuration. */
29 af3a75b4 2022-12-02 op 
30 af3a75b4 2022-12-02 op 	if (ruid != euid || euid != suid) {
31 af3a75b4 2022-12-02 op 		errno = ENOSYS;
32 af3a75b4 2022-12-02 op 		return -1;
33 af3a75b4 2022-12-02 op 	}
34 af3a75b4 2022-12-02 op 	ouid = getuid();
35 af3a75b4 2022-12-02 op 
36 af3a75b4 2022-12-02 op 	if ((ret = setreuid(euid, euid)) == -1)
37 af3a75b4 2022-12-02 op 		return -1;
38 af3a75b4 2022-12-02 op 
39 af3a75b4 2022-12-02 op 	/*
40 af3a75b4 2022-12-02 op 	 * When real, effective and saved uids are the same and we have
41 af3a75b4 2022-12-02 op 	 * changed uids, sanity check that we cannot restore the old uid.
42 af3a75b4 2022-12-02 op 	 */
43 af3a75b4 2022-12-02 op 
44 af3a75b4 2022-12-02 op 	if (ruid == euid && euid == suid && ouid != ruid &&
45 af3a75b4 2022-12-02 op 	    setuid(ouid) != -1 && seteuid(ouid) != -1) {
46 af3a75b4 2022-12-02 op 		errno = EINVAL;
47 af3a75b4 2022-12-02 op 		return -1;
48 af3a75b4 2022-12-02 op 	}
49 af3a75b4 2022-12-02 op 
50 af3a75b4 2022-12-02 op 	/*
51 af3a75b4 2022-12-02 op 	 * Finally, check that the real and effective uids are what we
52 af3a75b4 2022-12-02 op 	 * expect.
53 af3a75b4 2022-12-02 op 	 */
54 af3a75b4 2022-12-02 op 	if (getuid() != ruid || geteuid() != euid) {
55 af3a75b4 2022-12-02 op 		errno = EACCES;
56 af3a75b4 2022-12-02 op 		return -1;
57 af3a75b4 2022-12-02 op 	}
58 af3a75b4 2022-12-02 op 
59 af3a75b4 2022-12-02 op 	return ret;
60 af3a75b4 2022-12-02 op }