uidswap.c revision 106121 
1/*
2 * Author: Tatu Ylonen <ylo@cs.hut.fi>
3 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
4 *                    All rights reserved
5 * Code for uid-swapping.
6 *
7 * As far as I am concerned, the code I have written for this software
8 * can be used freely for any purpose.  Any derived versions of this
9 * software must be clearly marked as such, and if the derived work is
10 * incompatible with the protocol description in the RFC file, it must be
11 * called by a name other than "ssh" or "Secure Shell".
12 */
13
14#include "includes.h"
15RCSID("$OpenBSD: uidswap.c,v 1.23 2002/07/15 17:15:31 stevesk Exp $");
16
17#include "log.h"
18#include "uidswap.h"
19
20/*
21 * Note: all these functions must work in all of the following cases:
22 *    1. euid=0, ruid=0
23 *    2. euid=0, ruid!=0
24 *    3. euid!=0, ruid!=0
25 * Additionally, they must work regardless of whether the system has
26 * POSIX saved uids or not.
27 */
28
29#if defined(_POSIX_SAVED_IDS) && !defined(BROKEN_SAVED_UIDS)
30/* Lets assume that posix saved ids also work with seteuid, even though that
31   is not part of the posix specification. */
32#define SAVED_IDS_WORK_WITH_SETEUID
33/* Saved effective uid. */
34static uid_t 	saved_euid = 0;
35static gid_t	saved_egid = 0;
36#endif
37
38/* Saved effective uid. */
39static int	privileged = 0;
40static int	temporarily_use_uid_effective = 0;
41static gid_t	saved_egroups[NGROUPS_MAX], user_groups[NGROUPS_MAX];
42static int	saved_egroupslen = -1, user_groupslen = -1;
43
44/*
45 * Temporarily changes to the given uid.  If the effective user
46 * id is not root, this does nothing.  This call cannot be nested.
47 */
48void
49temporarily_use_uid(struct passwd *pw)
50{
51	/* Save the current euid, and egroups. */
52#ifdef SAVED_IDS_WORK_WITH_SETEUID
53	saved_euid = geteuid();
54	saved_egid = getegid();
55	debug("temporarily_use_uid: %u/%u (e=%u/%u)",
56	    (u_int)pw->pw_uid, (u_int)pw->pw_gid,
57	    (u_int)saved_euid, (u_int)saved_egid);
58	if (saved_euid != 0) {
59		privileged = 0;
60		return;
61	}
62#else
63	if (geteuid() != 0) {
64		privileged = 0;
65		return;
66	}
67#endif /* SAVED_IDS_WORK_WITH_SETEUID */
68
69	privileged = 1;
70	temporarily_use_uid_effective = 1;
71	saved_egroupslen = getgroups(NGROUPS_MAX, saved_egroups);
72	if (saved_egroupslen < 0)
73		fatal("getgroups: %.100s", strerror(errno));
74
75	/* set and save the user's groups */
76	if (user_groupslen == -1) {
77		if (initgroups(pw->pw_name, pw->pw_gid) < 0)
78			fatal("initgroups: %s: %.100s", pw->pw_name,
79			    strerror(errno));
80		user_groupslen = getgroups(NGROUPS_MAX, user_groups);
81		if (user_groupslen < 0)
82			fatal("getgroups: %.100s", strerror(errno));
83	}
84	/* Set the effective uid to the given (unprivileged) uid. */
85	if (setgroups(user_groupslen, user_groups) < 0)
86		fatal("setgroups: %.100s", strerror(errno));
87#ifndef SAVED_IDS_WORK_WITH_SETEUID
88	/* Propagate the privileged gid to all of our gids. */
89	if (setgid(getegid()) < 0)
90		debug("setgid %u: %.100s", (u_int) getegid(), strerror(errno));
91	/* Propagate the privileged uid to all of our uids. */
92	if (setuid(geteuid()) < 0)
93		debug("setuid %u: %.100s", (u_int) geteuid(), strerror(errno));
94#endif /* SAVED_IDS_WORK_WITH_SETEUID */
95	if (setegid(pw->pw_gid) < 0)
96		fatal("setegid %u: %.100s", (u_int)pw->pw_gid,
97		    strerror(errno));
98	if (seteuid(pw->pw_uid) == -1)
99		fatal("seteuid %u: %.100s", (u_int)pw->pw_uid,
100		    strerror(errno));
101}
102
103/*
104 * Restores to the original (privileged) uid.
105 */
106void
107restore_uid(void)
108{
109	/* it's a no-op unless privileged */
110	if (!privileged) {
111		debug("restore_uid: (unprivileged)");
112		return;
113	}
114	if (!temporarily_use_uid_effective)
115		fatal("restore_uid: temporarily_use_uid not effective");
116
117#ifdef SAVED_IDS_WORK_WITH_SETEUID
118	debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid);
119	/* Set the effective uid back to the saved privileged uid. */
120	if (seteuid(saved_euid) < 0)
121		fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno));
122	if (setegid(saved_egid) < 0)
123		fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno));
124#else /* SAVED_IDS_WORK_WITH_SETEUID */
125	/*
126	 * We are unable to restore the real uid to its unprivileged value.
127	 * Propagate the real uid (usually more privileged) to effective uid
128	 * as well.
129	 */
130	setuid(getuid());
131	setgid(getgid());
132#endif /* SAVED_IDS_WORK_WITH_SETEUID */
133
134	if (setgroups(saved_egroupslen, saved_egroups) < 0)
135		fatal("setgroups: %.100s", strerror(errno));
136	temporarily_use_uid_effective = 0;
137}
138
139/*
140 * Permanently sets all uids to the given uid.  This cannot be
141 * called while temporarily_use_uid is effective.
142 */
143void
144permanently_set_uid(struct passwd *pw)
145{
146	if (temporarily_use_uid_effective)
147		fatal("permanently_set_uid: temporarily_use_uid effective");
148	debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid,
149	    (u_int)pw->pw_gid);
150	if (setgid(pw->pw_gid) < 0)
151		fatal("setgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
152	if (setuid(pw->pw_uid) < 0)
153		fatal("setuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
154}
155