xref: /titanic_41/usr/src/cmd/ssh/libssh/common/uidswap.c (revision fe1c642d06e14b412cd83ae2179303186ab08972)
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  * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
15  * Use is subject to license terms.
16  */
17 
18 #include "includes.h"
19 RCSID("$OpenBSD: uidswap.c,v 1.23 2002/07/15 17:15:31 stevesk Exp $");
20 
21 #include <priv.h>
22 
23 #include "log.h"
24 #include "uidswap.h"
25 #include "buffer.h"
26 #include "servconf.h"
27 
28 /*
29  * Note: all these functions must work in all of the following cases:
30  *    1. euid=0, ruid=0
31  *    2. euid=0, ruid!=0
32  *    3. euid!=0, ruid!=0
33  * Additionally, they must work regardless of whether the system has
34  * POSIX saved uids or not.
35  */
36 
37 #if defined(_POSIX_SAVED_IDS) && !defined(BROKEN_SAVED_UIDS)
38 /* Lets assume that posix saved ids also work with seteuid, even though that
39    is not part of the posix specification. */
40 #define SAVED_IDS_WORK
41 /* Saved effective uid. */
42 static uid_t 	saved_euid = 0;
43 static gid_t	saved_egid = 0;
44 #endif
45 
46 /* Saved effective uid. */
47 static int	privileged = 0;
48 static int	temporarily_use_uid_effective = 0;
49 static int	ngroups_max = -1;
50 static gid_t	*saved_egroups, *user_groups;
51 static int	saved_egroupslen = -1, user_groupslen = -1;
52 
53 /*
54  * Temporarily changes to the given uid.  If the effective user
55  * id is not root, this does nothing.  This call cannot be nested.
56  */
57 void
58 temporarily_use_uid(struct passwd *pw)
59 {
60 	/* Save the current euid, and egroups. */
61 #ifdef SAVED_IDS_WORK
62 	saved_euid = geteuid();
63 	saved_egid = getegid();
64 	debug("temporarily_use_uid: %u/%u (e=%u/%u)",
65 	    (u_int)pw->pw_uid, (u_int)pw->pw_gid,
66 	    (u_int)saved_euid, (u_int)saved_egid);
67 	if (saved_euid != 0) {
68 		privileged = 0;
69 		return;
70 	}
71 #else
72 	if (geteuid() != 0) {
73 		privileged = 0;
74 		return;
75 	}
76 #endif /* SAVED_IDS_WORK */
77 
78 	privileged = 1;
79 	temporarily_use_uid_effective = 1;
80 
81 	if (ngroups_max < 0) {
82 		ngroups_max = sysconf(_SC_NGROUPS_MAX);
83 		saved_egroups = malloc(ngroups_max * sizeof (gid_t));
84 		user_groups = malloc(ngroups_max * sizeof (gid_t));
85 		if (saved_egroups == NULL || user_groups == NULL)
86 			fatal("malloc(gid array): %.100s", strerror(errno));
87 	}
88 
89 	saved_egroupslen = getgroups(ngroups_max, saved_egroups);
90 	if (saved_egroupslen < 0)
91 		fatal("getgroups: %.100s", strerror(errno));
92 
93 	/* set and save the user's groups */
94 	if (user_groupslen == -1) {
95 		if (initgroups(pw->pw_name, pw->pw_gid) < 0)
96 			fatal("initgroups: %s: %.100s", pw->pw_name,
97 			    strerror(errno));
98 		user_groupslen = getgroups(ngroups_max, user_groups);
99 		if (user_groupslen < 0)
100 			fatal("getgroups: %.100s", strerror(errno));
101 	}
102 	/* Set the effective uid to the given (unprivileged) uid. */
103 	if (setgroups(user_groupslen, user_groups) < 0)
104 		fatal("setgroups: %.100s", strerror(errno));
105 #ifdef SAVED_IDS_WORK
106 	/* Set saved gid and set real gid */
107 	if (setregid(pw->pw_gid, -1) == -1)
108 		debug("setregid(%u, -1): %.100s", (uint_t)pw->pw_gid, strerror(errno));
109 	/* Set saved uid and set real uid */
110 	if (setreuid(pw->pw_uid, -1) == -1)
111 		debug("setreuid(%u, -1): %.100s", (uint_t)pw->pw_uid, strerror(errno));
112 #else
113 	/* Propagate the privileged gid to all of our gids. */
114 	if (setgid(getegid()) < 0)
115 		debug("setgid %u: %.100s", (u_int) getegid(), strerror(errno));
116 	/* Propagate the privileged uid to all of our uids. */
117 	if (setuid(geteuid()) < 0)
118 		debug("setuid %u: %.100s", (u_int) geteuid(), strerror(errno));
119 #endif /* SAVED_IDS_WORK */
120 	/* Set effective gid */
121 	if (setegid(pw->pw_gid) == -1)
122 		fatal("setegid %u: %.100s", (u_int)pw->pw_uid,
123 		    strerror(errno));
124 	/* Set effective uid */
125 	if (seteuid(pw->pw_uid) == -1)
126 		fatal("seteuid %u: %.100s", (u_int)pw->pw_uid,
127 		    strerror(errno));
128 	/*
129 	 * If saved set ids work then
130 	 *
131 	 *	ruid == euid == pw->pw_uid
132 	 *	saved uid = previous euid
133 	 *	rgid == egid == pw->pw_gid
134 	 *	saved gid = previous egid
135 	 */
136 }
137 
138 /*
139  * Restores to the original (privileged) uid.
140  */
141 void
142 restore_uid(void)
143 {
144 	/* it's a no-op unless privileged */
145 	if (!privileged) {
146 		debug("restore_uid: (unprivileged)");
147 		return;
148 	}
149 	if (!temporarily_use_uid_effective)
150 		fatal("restore_uid: temporarily_use_uid not effective");
151 
152 #ifdef SAVED_IDS_WORK
153 	debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid);
154 	/* Set the effective uid back to the saved privileged uid. */
155 	if (seteuid(saved_euid) < 0)
156 		fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno));
157 	if (setuid(saved_euid) < 0)
158 		fatal("setuid %u: %.100s", (u_int)saved_euid, strerror(errno));
159 	if (setegid(saved_egid) < 0)
160 		fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno));
161 	if (setgid(saved_egid) < 0)
162 		fatal("setgid %u: %.100s", (u_int)saved_egid, strerror(errno));
163 #else /* SAVED_IDS_WORK */
164 	/*
165 	 * We are unable to restore the real uid to its unprivileged value.
166 	 * Propagate the real uid (usually more privileged) to effective uid
167 	 * as well.
168 	 */
169 	setuid(getuid());
170 	setgid(getgid());
171 #endif /* SAVED_IDS_WORK */
172 
173 	if (setgroups(saved_egroupslen, saved_egroups) < 0)
174 		fatal("setgroups: %.100s", strerror(errno));
175 	temporarily_use_uid_effective = 0;
176 }
177 
178 /*
179  * Permanently sets all uids to the given uid. This cannot be called while
180  * temporarily_use_uid is effective. Note that when the ChrootDirectory option
181  * is in use we keep a few privileges so that we can call chroot(2) later while
182  * already running under UIDs of a connecting user.
183  */
184 void
185 permanently_set_uid(struct passwd *pw, char *chroot_directory)
186 {
187 	priv_set_t *pset;
188 
189 	if (temporarily_use_uid_effective)
190 		fatal("%s: temporarily_use_uid effective", __func__);
191 
192 	debug("%s: %u/%u", __func__, (u_int)pw->pw_uid, (u_int)pw->pw_gid);
193 
194 	if (initgroups(pw->pw_name, pw->pw_gid) < 0)
195 		fatal("initgroups: %s: %.100s", pw->pw_name,
196 		    strerror(errno));
197 
198 	if (setgid(pw->pw_gid) < 0)
199 		fatal("setgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
200 
201 	/*
202 	 * If root is connecting we are done now. Note that we must have called
203 	 * setgid() in case that the SSH server was run under a group other than
204 	 * root.
205 	 */
206 	if (pw->pw_uid == 0)
207 		return;
208 
209 	/*
210 	 * This means we will keep all privileges after the UID change.
211 	 */
212 	if (setpflags(PRIV_AWARE, 1) != 0)
213 		fatal("setpflags: %s", strerror(errno));
214 
215 	/* Now we are running under UID of the user. */
216 	if (setuid(pw->pw_uid) < 0)
217 		fatal("setuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
218 
219 	/*
220 	 * We will run with the privileges from the Inheritable set as
221 	 * we would have after exec(2) if we had stayed in NPA mode
222 	 * before setuid(2) call (see privileges(5), user_attr(4), and
223 	 * pam_unix_cred(5)). We want to run with P = E = I, with I as
224 	 * set by pam_unix_cred(5). We also add PRIV_PROC_CHROOT,
225 	 * obviously, and then PRIV_PROC_FORK and PRIV_PROC_EXEC, since
226 	 * those two might have been removed from the I set. Note that
227 	 * we are expected to finish the login process without them in
228 	 * the I set, the important thing is that those not be passed on
229 	 * to a shell or a subsystem later if they were not set in
230 	 * pam_unix_cred(5).
231 	 */
232 	if ((pset = priv_allocset()) == NULL)
233 		fatal("priv_allocset: %s", strerror(errno));
234 	if (getppriv(PRIV_INHERITABLE, pset) != 0)
235 		fatal("getppriv: %s", strerror(errno));
236 
237 	/* We do not need PRIV_PROC_CHROOT unless chroot()ing. */
238 	if (chroot_requested(chroot_directory) &&
239 	    priv_addset(pset, PRIV_PROC_CHROOT) == -1) {
240 		fatal("%s: priv_addset failed", __func__);
241 	}
242 
243 	if (priv_addset(pset, PRIV_PROC_FORK) == -1 ||
244 	    priv_addset(pset, PRIV_PROC_EXEC) == -1) {
245 		fatal("%s: priv_addset failed", __func__);
246 	}
247 
248 	/* Set only P; this will also set E. */
249 	if (setppriv(PRIV_SET, PRIV_PERMITTED, pset) == -1)
250 		fatal("setppriv: %s", strerror(errno));
251 
252 	/* We don't need the PA flag anymore. */
253 	if (setpflags(PRIV_AWARE, 0) == -1)
254 		fatal("setpflags: %s", strerror(errno));
255 
256 	priv_freeset(pset);
257 }
258