1 bd8683d0 2022-12-02 op /*
 2 bd8683d0 2022-12-02 op  * Copyright (c) 2004, 2005 Darren Tucker (dtucker at zip com au).
 3 bd8683d0 2022-12-02 op  *
 4 bd8683d0 2022-12-02 op  * Permission to use, copy, modify, and distribute this software for any
 5 bd8683d0 2022-12-02 op  * purpose with or without fee is hereby granted, provided that the above
 6 bd8683d0 2022-12-02 op  * copyright notice and this permission notice appear in all copies.
 7 bd8683d0 2022-12-02 op  *
 8 bd8683d0 2022-12-02 op  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 9 bd8683d0 2022-12-02 op  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
10 bd8683d0 2022-12-02 op  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
11 bd8683d0 2022-12-02 op  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
12 bd8683d0 2022-12-02 op  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
13 bd8683d0 2022-12-02 op  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
14 bd8683d0 2022-12-02 op  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
15 bd8683d0 2022-12-02 op  */
16 bd8683d0 2022-12-02 op 
17 bd8683d0 2022-12-02 op #include <sys/types.h>
18 bd8683d0 2022-12-02 op 
19 bd8683d0 2022-12-02 op #include <errno.h>
20 bd8683d0 2022-12-02 op #include <unistd.h>
21 bd8683d0 2022-12-02 op 
22 bd8683d0 2022-12-02 op int
23 bd8683d0 2022-12-02 op setresuid(uid_t ruid, uid_t euid, uid_t suid)
24 bd8683d0 2022-12-02 op {
25 bd8683d0 2022-12-02 op 	uid_t ouid;
26 bd8683d0 2022-12-02 op 	int ret = -1;
27 bd8683d0 2022-12-02 op 
28 bd8683d0 2022-12-02 op 	/* Allow only the tested configuration. */
29 bd8683d0 2022-12-02 op 
30 bd8683d0 2022-12-02 op 	if (ruid != euid || euid != suid) {
31 bd8683d0 2022-12-02 op 		errno = ENOSYS;
32 bd8683d0 2022-12-02 op 		return -1;
33 bd8683d0 2022-12-02 op 	}
34 bd8683d0 2022-12-02 op 	ouid = getuid();
35 bd8683d0 2022-12-02 op 
36 bd8683d0 2022-12-02 op 	if ((ret = setreuid(euid, euid)) == -1)
37 bd8683d0 2022-12-02 op 		return -1;
38 bd8683d0 2022-12-02 op 
39 bd8683d0 2022-12-02 op 	/*
40 bd8683d0 2022-12-02 op 	 * When real, effective and saved uids are the same and we have
41 bd8683d0 2022-12-02 op 	 * changed uids, sanity check that we cannot restore the old uid.
42 bd8683d0 2022-12-02 op 	 */
43 bd8683d0 2022-12-02 op 
44 bd8683d0 2022-12-02 op 	if (ruid == euid && euid == suid && ouid != ruid &&
45 bd8683d0 2022-12-02 op 	    setuid(ouid) != -1 && seteuid(ouid) != -1) {
46 bd8683d0 2022-12-02 op 		errno = EINVAL;
47 bd8683d0 2022-12-02 op 		return -1;
48 bd8683d0 2022-12-02 op 	}
49 bd8683d0 2022-12-02 op 
50 bd8683d0 2022-12-02 op 	/*
51 bd8683d0 2022-12-02 op 	 * Finally, check that the real and effective uids are what we
52 bd8683d0 2022-12-02 op 	 * expect.
53 bd8683d0 2022-12-02 op 	 */
54 bd8683d0 2022-12-02 op 	if (getuid() != ruid || geteuid() != euid) {
55 bd8683d0 2022-12-02 op 		errno = EACCES;
56 bd8683d0 2022-12-02 op 		return -1;
57 bd8683d0 2022-12-02 op 	}
58 bd8683d0 2022-12-02 op 
59 bd8683d0 2022-12-02 op 	return ret;
60 bd8683d0 2022-12-02 op }