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 }