1 /* $OpenBSD: uidswap.c,v 1.37 2015/01/16 06:40:12 deraadt Exp $ */
2 /*
3 * Author: Tatu Ylonen <ylo@cs.hut.fi>
4 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5 * All rights reserved
6 * Code for uid-swapping.
7 *
8 * As far as I am concerned, the code I have written for this software
9 * can be used freely for any purpose. Any derived versions of this
10 * software must be clearly marked as such, and if the derived work is
11 * incompatible with the protocol description in the RFC file, it must be
12 * called by a name other than "ssh" or "Secure Shell".
13 */
14
15 #include "includes.h"
16
17 #include <errno.h>
18 #include <pwd.h>
19 #include <string.h>
20 #include <unistd.h>
21 #include <limits.h>
22 #include <stdarg.h>
23 #include <stdlib.h>
24
25 #include <grp.h>
26
27 #include "log.h"
28 #include "uidswap.h"
29 #include "xmalloc.h"
30
31 #ifdef ANDROID
32 #include <private/android_filesystem_config.h>
33 #include <sys/capability.h>
34 #include <sys/prctl.h>
35 #endif
36
37 /*
38 * Note: all these functions must work in all of the following cases:
39 * 1. euid=0, ruid=0
40 * 2. euid=0, ruid!=0
41 * 3. euid!=0, ruid!=0
42 * Additionally, they must work regardless of whether the system has
43 * POSIX saved uids or not.
44 */
45
46 #if defined(_POSIX_SAVED_IDS) && !defined(BROKEN_SAVED_UIDS)
47 /* Lets assume that posix saved ids also work with seteuid, even though that
48 is not part of the posix specification. */
49 #define SAVED_IDS_WORK_WITH_SETEUID
50 /* Saved effective uid. */
51 static uid_t saved_euid = 0;
52 static gid_t saved_egid = 0;
53 #endif
54
55 /* Saved effective uid. */
56 static int privileged = 0;
57 static int temporarily_use_uid_effective = 0;
58 static gid_t *saved_egroups = NULL, *user_groups = NULL;
59 static int saved_egroupslen = -1, user_groupslen = -1;
60
61 /*
62 * Temporarily changes to the given uid. If the effective user
63 * id is not root, this does nothing. This call cannot be nested.
64 */
65 void
temporarily_use_uid(struct passwd * pw)66 temporarily_use_uid(struct passwd *pw)
67 {
68 /* Save the current euid, and egroups. */
69 #ifdef SAVED_IDS_WORK_WITH_SETEUID
70 saved_euid = geteuid();
71 saved_egid = getegid();
72 debug("temporarily_use_uid: %u/%u (e=%u/%u)",
73 (u_int)pw->pw_uid, (u_int)pw->pw_gid,
74 (u_int)saved_euid, (u_int)saved_egid);
75 #ifndef HAVE_CYGWIN
76 if (saved_euid != 0) {
77 privileged = 0;
78 return;
79 }
80 #endif
81 #else
82 if (geteuid() != 0) {
83 privileged = 0;
84 return;
85 }
86 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
87
88 privileged = 1;
89 temporarily_use_uid_effective = 1;
90
91 saved_egroupslen = getgroups(0, NULL);
92 if (saved_egroupslen < 0)
93 fatal("getgroups: %.100s", strerror(errno));
94 if (saved_egroupslen > 0) {
95 saved_egroups = xrealloc(saved_egroups,
96 saved_egroupslen, sizeof(gid_t));
97 if (getgroups(saved_egroupslen, saved_egroups) < 0)
98 fatal("getgroups: %.100s", strerror(errno));
99 } else { /* saved_egroupslen == 0 */
100 free(saved_egroups);
101 }
102
103 /* set and save the user's groups */
104 if (user_groupslen == -1) {
105 if (initgroups(pw->pw_name, pw->pw_gid) < 0)
106 fatal("initgroups: %s: %.100s", pw->pw_name,
107 strerror(errno));
108
109 user_groupslen = getgroups(0, NULL);
110 if (user_groupslen < 0)
111 fatal("getgroups: %.100s", strerror(errno));
112 if (user_groupslen > 0) {
113 user_groups = xrealloc(user_groups,
114 user_groupslen, sizeof(gid_t));
115 if (getgroups(user_groupslen, user_groups) < 0)
116 fatal("getgroups: %.100s", strerror(errno));
117 } else { /* user_groupslen == 0 */
118 free(user_groups);
119 }
120 }
121 /* Set the effective uid to the given (unprivileged) uid. */
122 if (setgroups(user_groupslen, user_groups) < 0)
123 fatal("setgroups: %.100s", strerror(errno));
124 #ifndef SAVED_IDS_WORK_WITH_SETEUID
125 /* Propagate the privileged gid to all of our gids. */
126 if (setgid(getegid()) < 0)
127 debug("setgid %u: %.100s", (u_int) getegid(), strerror(errno));
128 /* Propagate the privileged uid to all of our uids. */
129 if (setuid(geteuid()) < 0)
130 debug("setuid %u: %.100s", (u_int) geteuid(), strerror(errno));
131 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
132 if (setegid(pw->pw_gid) < 0)
133 fatal("setegid %u: %.100s", (u_int)pw->pw_gid,
134 strerror(errno));
135 if (seteuid(pw->pw_uid) == -1)
136 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid,
137 strerror(errno));
138 }
139
140 void
permanently_drop_suid(uid_t uid)141 permanently_drop_suid(uid_t uid)
142 {
143 #ifndef HAVE_CYGWIN
144 uid_t old_uid = getuid();
145 #endif
146
147 debug("permanently_drop_suid: %u", (u_int)uid);
148 if (setresuid(uid, uid, uid) < 0)
149 fatal("setresuid %u: %.100s", (u_int)uid, strerror(errno));
150
151 #ifndef HAVE_CYGWIN
152 /* Try restoration of UID if changed (test clearing of saved uid) */
153 if (old_uid != uid &&
154 (setuid(old_uid) != -1 || seteuid(old_uid) != -1))
155 fatal("%s: was able to restore old [e]uid", __func__);
156 #endif
157
158 /* Verify UID drop was successful */
159 if (getuid() != uid || geteuid() != uid) {
160 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)",
161 __func__, (u_int)getuid(), (u_int)geteuid(), (u_int)uid);
162 }
163 }
164
165 /*
166 * Restores to the original (privileged) uid.
167 */
168 void
restore_uid(void)169 restore_uid(void)
170 {
171 /* it's a no-op unless privileged */
172 if (!privileged) {
173 debug("restore_uid: (unprivileged)");
174 return;
175 }
176 if (!temporarily_use_uid_effective)
177 fatal("restore_uid: temporarily_use_uid not effective");
178
179 #ifdef SAVED_IDS_WORK_WITH_SETEUID
180 debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid);
181 /* Set the effective uid back to the saved privileged uid. */
182 if (seteuid(saved_euid) < 0)
183 fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno));
184 if (setegid(saved_egid) < 0)
185 fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno));
186 #else /* SAVED_IDS_WORK_WITH_SETEUID */
187 /*
188 * We are unable to restore the real uid to its unprivileged value.
189 * Propagate the real uid (usually more privileged) to effective uid
190 * as well.
191 */
192 setuid(getuid());
193 setgid(getgid());
194 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
195
196 if (setgroups(saved_egroupslen, saved_egroups) < 0)
197 fatal("setgroups: %.100s", strerror(errno));
198 temporarily_use_uid_effective = 0;
199 }
200
201 /*
202 * Permanently sets all uids to the given uid. This cannot be
203 * called while temporarily_use_uid is effective.
204 */
205 void
permanently_set_uid(struct passwd * pw)206 permanently_set_uid(struct passwd *pw)
207 {
208 #ifndef HAVE_CYGWIN
209 uid_t old_uid = getuid();
210 gid_t old_gid = getgid();
211 #endif
212 #if defined(ANDROID)
213 struct __user_cap_header_struct header;
214 struct __user_cap_data_struct cap;
215 #endif
216
217 if (pw == NULL)
218 fatal("permanently_set_uid: no user given");
219 if (temporarily_use_uid_effective)
220 fatal("permanently_set_uid: temporarily_use_uid effective");
221 debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid,
222 (u_int)pw->pw_gid);
223
224 #if defined(ANDROID)
225 if (pw->pw_uid == AID_SHELL) {
226 prctl(PR_SET_KEEPCAPS, 1, 0, 0, 0);
227
228 /* add extra groups needed for shell user:
229 * - AID_LOG to read system logs (adb logcat)
230 * - AID_INPUT to diagnose input issues (getevent)
231 * - AID_INET to diagnose network issues (netcfg, ping)
232 * - AID_GRAPHICS to access the frame buffer
233 * - AID_NET_BT and AID_NET_BT_ADMIN to diagnose bluetooth (hcidump)
234 * - AID_SDCARD_RW to allow writing to the SD card
235 * - AID_MOUNT to allow unmounting the SD card before rebooting
236 * - AID_NET_BW_STATS to read out qtaguid statistics. */
237 gid_t groups[] = {AID_LOG, AID_INPUT, AID_INET,
238 AID_GRAPHICS, AID_NET_BT, AID_NET_BT_ADMIN,
239 AID_SDCARD_RW, AID_MOUNT, AID_NET_BW_STATS};
240 setgroups(sizeof(groups)/sizeof(groups[0]), groups);
241 }
242 #endif
243
244 if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) < 0)
245 fatal("setresgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
246
247 #ifdef __APPLE__
248 /*
249 * OS X requires initgroups after setgid to opt back into
250 * memberd support for >16 supplemental groups.
251 */
252 if (initgroups(pw->pw_name, pw->pw_gid) < 0)
253 fatal("initgroups %.100s %u: %.100s",
254 pw->pw_name, (u_int)pw->pw_gid, strerror(errno));
255 #endif
256
257 if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) < 0)
258 fatal("setresuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
259
260 #ifndef HAVE_CYGWIN
261 /* Try restoration of GID if changed (test clearing of saved gid) */
262 if (old_gid != pw->pw_gid && pw->pw_uid != 0 &&
263 (setgid(old_gid) != -1 || setegid(old_gid) != -1))
264 fatal("%s: was able to restore old [e]gid", __func__);
265 #endif
266
267 /* Verify GID drop was successful */
268 if (getgid() != pw->pw_gid || getegid() != pw->pw_gid) {
269 fatal("%s: egid incorrect gid:%u egid:%u (should be %u)",
270 __func__, (u_int)getgid(), (u_int)getegid(),
271 (u_int)pw->pw_gid);
272 }
273
274 #ifndef HAVE_CYGWIN
275 /* Try restoration of UID if changed (test clearing of saved uid) */
276 if (old_uid != pw->pw_uid &&
277 (setuid(old_uid) != -1 || seteuid(old_uid) != -1))
278 fatal("%s: was able to restore old [e]uid", __func__);
279 #endif
280
281 /* Verify UID drop was successful */
282 if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid) {
283 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)",
284 __func__, (u_int)getuid(), (u_int)geteuid(),
285 (u_int)pw->pw_uid);
286 }
287
288 #ifdef ANDROID
289 if (pw->pw_uid == AID_SHELL) {
290 /* set CAP_SYS_BOOT capability, so "adb reboot" will succeed */
291 header.version = _LINUX_CAPABILITY_VERSION;
292 header.pid = 0;
293 cap.effective = cap.permitted = (1 << CAP_SYS_BOOT);
294 cap.inheritable = 0;
295 capset(&header, &cap);
296 }
297 #endif
298
299 }
300