1 /* $OpenBSD: uidswap.c,v 1.39 2015/06/24 01:49:19 dtucker 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 #if !defined(GCE_PLATFORM_SDK_VERSION) || (GCE_PLATFORM_SDK_VERSION > 17)
34 #include <sys/capability.h>
35 #else
36 #include <linux/capability.h>
37 #endif
38 #include <sys/prctl.h>
39 #endif
40
41 /*
42 * Note: all these functions must work in all of the following cases:
43 * 1. euid=0, ruid=0
44 * 2. euid=0, ruid!=0
45 * 3. euid!=0, ruid!=0
46 * Additionally, they must work regardless of whether the system has
47 * POSIX saved uids or not.
48 */
49
50 #if defined(_POSIX_SAVED_IDS) && !defined(BROKEN_SAVED_UIDS)
51 /* Lets assume that posix saved ids also work with seteuid, even though that
52 is not part of the posix specification. */
53 #define SAVED_IDS_WORK_WITH_SETEUID
54 /* Saved effective uid. */
55 static uid_t saved_euid = 0;
56 static gid_t saved_egid = 0;
57 #endif
58
59 /* Saved effective uid. */
60 static int privileged = 0;
61 static int temporarily_use_uid_effective = 0;
62 static gid_t *saved_egroups = NULL, *user_groups = NULL;
63 static int saved_egroupslen = -1, user_groupslen = -1;
64
65 /*
66 * Temporarily changes to the given uid. If the effective user
67 * id is not root, this does nothing. This call cannot be nested.
68 */
69 void
temporarily_use_uid(struct passwd * pw)70 temporarily_use_uid(struct passwd *pw)
71 {
72 /* Save the current euid, and egroups. */
73 #ifdef SAVED_IDS_WORK_WITH_SETEUID
74 saved_euid = geteuid();
75 saved_egid = getegid();
76 debug("temporarily_use_uid: %u/%u (e=%u/%u)",
77 (u_int)pw->pw_uid, (u_int)pw->pw_gid,
78 (u_int)saved_euid, (u_int)saved_egid);
79 #ifndef HAVE_CYGWIN
80 if (saved_euid != 0) {
81 privileged = 0;
82 return;
83 }
84 #endif
85 #else
86 if (geteuid() != 0) {
87 privileged = 0;
88 return;
89 }
90 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
91
92 privileged = 1;
93 temporarily_use_uid_effective = 1;
94
95 saved_egroupslen = getgroups(0, NULL);
96 if (saved_egroupslen < 0)
97 fatal("getgroups: %.100s", strerror(errno));
98 if (saved_egroupslen > 0) {
99 saved_egroups = xreallocarray(saved_egroups,
100 saved_egroupslen, sizeof(gid_t));
101 if (getgroups(saved_egroupslen, saved_egroups) < 0)
102 fatal("getgroups: %.100s", strerror(errno));
103 } else { /* saved_egroupslen == 0 */
104 free(saved_egroups);
105 }
106
107 /* set and save the user's groups */
108 if (user_groupslen == -1) {
109 if (initgroups(pw->pw_name, pw->pw_gid) < 0)
110 fatal("initgroups: %s: %.100s", pw->pw_name,
111 strerror(errno));
112
113 user_groupslen = getgroups(0, NULL);
114 if (user_groupslen < 0)
115 fatal("getgroups: %.100s", strerror(errno));
116 if (user_groupslen > 0) {
117 user_groups = xreallocarray(user_groups,
118 user_groupslen, sizeof(gid_t));
119 if (getgroups(user_groupslen, user_groups) < 0)
120 fatal("getgroups: %.100s", strerror(errno));
121 } else { /* user_groupslen == 0 */
122 free(user_groups);
123 }
124 }
125 /* Set the effective uid to the given (unprivileged) uid. */
126 if (setgroups(user_groupslen, user_groups) < 0)
127 fatal("setgroups: %.100s", strerror(errno));
128 #ifndef SAVED_IDS_WORK_WITH_SETEUID
129 /* Propagate the privileged gid to all of our gids. */
130 if (setgid(getegid()) < 0)
131 debug("setgid %u: %.100s", (u_int) getegid(), strerror(errno));
132 /* Propagate the privileged uid to all of our uids. */
133 if (setuid(geteuid()) < 0)
134 debug("setuid %u: %.100s", (u_int) geteuid(), strerror(errno));
135 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
136 if (setegid(pw->pw_gid) < 0)
137 fatal("setegid %u: %.100s", (u_int)pw->pw_gid,
138 strerror(errno));
139 if (seteuid(pw->pw_uid) == -1)
140 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid,
141 strerror(errno));
142 }
143
144 void
permanently_drop_suid(uid_t uid)145 permanently_drop_suid(uid_t uid)
146 {
147 #ifndef NO_UID_RESTORATION_TEST
148 uid_t old_uid = getuid();
149 #endif
150
151 debug("permanently_drop_suid: %u", (u_int)uid);
152 if (setresuid(uid, uid, uid) < 0)
153 fatal("setresuid %u: %.100s", (u_int)uid, strerror(errno));
154
155 #ifndef NO_UID_RESTORATION_TEST
156 /*
157 * Try restoration of UID if changed (test clearing of saved uid).
158 *
159 * Note that we don't do this on Cygwin, or on Solaris-based platforms
160 * where fine-grained privileges are available (the user might be
161 * deliberately allowed the right to setuid back to root).
162 */
163 if (old_uid != uid &&
164 (setuid(old_uid) != -1 || seteuid(old_uid) != -1))
165 fatal("%s: was able to restore old [e]uid", __func__);
166 #endif
167
168 /* Verify UID drop was successful */
169 if (getuid() != uid || geteuid() != uid) {
170 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)",
171 __func__, (u_int)getuid(), (u_int)geteuid(), (u_int)uid);
172 }
173 }
174
175 /*
176 * Restores to the original (privileged) uid.
177 */
178 void
restore_uid(void)179 restore_uid(void)
180 {
181 /* it's a no-op unless privileged */
182 if (!privileged) {
183 debug("restore_uid: (unprivileged)");
184 return;
185 }
186 if (!temporarily_use_uid_effective)
187 fatal("restore_uid: temporarily_use_uid not effective");
188
189 #ifdef SAVED_IDS_WORK_WITH_SETEUID
190 debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid);
191 /* Set the effective uid back to the saved privileged uid. */
192 if (seteuid(saved_euid) < 0)
193 fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno));
194 if (setegid(saved_egid) < 0)
195 fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno));
196 #else /* SAVED_IDS_WORK_WITH_SETEUID */
197 /*
198 * We are unable to restore the real uid to its unprivileged value.
199 * Propagate the real uid (usually more privileged) to effective uid
200 * as well.
201 */
202 setuid(getuid());
203 setgid(getgid());
204 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
205
206 if (setgroups(saved_egroupslen, saved_egroups) < 0)
207 fatal("setgroups: %.100s", strerror(errno));
208 temporarily_use_uid_effective = 0;
209 }
210
211 /*
212 * Permanently sets all uids to the given uid. This cannot be
213 * called while temporarily_use_uid is effective.
214 */
215 void
permanently_set_uid(struct passwd * pw)216 permanently_set_uid(struct passwd *pw)
217 {
218 #ifndef NO_UID_RESTORATION_TEST
219 uid_t old_uid = getuid();
220 gid_t old_gid = getgid();
221 #endif
222 #if defined(ANDROID)
223 struct __user_cap_header_struct header;
224 struct __user_cap_data_struct cap;
225 #endif
226
227 if (pw == NULL)
228 fatal("permanently_set_uid: no user given");
229 if (temporarily_use_uid_effective)
230 fatal("permanently_set_uid: temporarily_use_uid effective");
231 debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid,
232 (u_int)pw->pw_gid);
233
234 #if defined(ANDROID)
235 if (pw->pw_uid == AID_SHELL) {
236 prctl(PR_SET_KEEPCAPS, 1, 0, 0, 0);
237
238 /* add extra groups needed for shell user:
239 * - AID_LOG to read system logs (adb logcat)
240 * - AID_INPUT to diagnose input issues (getevent)
241 * - AID_INET to diagnose network issues (netcfg, ping)
242 * - AID_GRAPHICS to access the frame buffer
243 * - AID_NET_BT and AID_NET_BT_ADMIN to diagnose bluetooth (hcidump)
244 * - AID_SDCARD_RW to allow writing to the SD card
245 * - AID_MOUNT to allow unmounting the SD card before rebooting
246 * - AID_NET_BW_STATS to read out qtaguid statistics. */
247 gid_t groups[] = {AID_LOG, AID_INPUT, AID_INET,
248 AID_GRAPHICS, AID_NET_BT, AID_NET_BT_ADMIN,
249 AID_SDCARD_RW, AID_MOUNT, AID_NET_BW_STATS};
250 setgroups(sizeof(groups)/sizeof(groups[0]), groups);
251 }
252 #endif
253
254 if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) < 0)
255 fatal("setresgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
256
257 #ifdef __APPLE__
258 /*
259 * OS X requires initgroups after setgid to opt back into
260 * memberd support for >16 supplemental groups.
261 */
262 if (initgroups(pw->pw_name, pw->pw_gid) < 0)
263 fatal("initgroups %.100s %u: %.100s",
264 pw->pw_name, (u_int)pw->pw_gid, strerror(errno));
265 #endif
266
267 if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) < 0)
268 fatal("setresuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
269
270 #ifndef NO_UID_RESTORATION_TEST
271 /* Try restoration of GID if changed (test clearing of saved gid) */
272 if (old_gid != pw->pw_gid && pw->pw_uid != 0 &&
273 (setgid(old_gid) != -1 || setegid(old_gid) != -1))
274 fatal("%s: was able to restore old [e]gid", __func__);
275 #endif
276
277 /* Verify GID drop was successful */
278 if (getgid() != pw->pw_gid || getegid() != pw->pw_gid) {
279 fatal("%s: egid incorrect gid:%u egid:%u (should be %u)",
280 __func__, (u_int)getgid(), (u_int)getegid(),
281 (u_int)pw->pw_gid);
282 }
283
284 #ifndef NO_UID_RESTORATION_TEST
285 /* Try restoration of UID if changed (test clearing of saved uid) */
286 if (old_uid != pw->pw_uid &&
287 (setuid(old_uid) != -1 || seteuid(old_uid) != -1))
288 fatal("%s: was able to restore old [e]uid", __func__);
289 #endif
290
291 /* Verify UID drop was successful */
292 if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid) {
293 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)",
294 __func__, (u_int)getuid(), (u_int)geteuid(),
295 (u_int)pw->pw_uid);
296 }
297
298 #ifdef ANDROID
299 if (pw->pw_uid == AID_SHELL) {
300 /* set CAP_SYS_BOOT capability, so "adb reboot" will succeed */
301 header.version = _LINUX_CAPABILITY_VERSION;
302 header.pid = 0;
303 cap.effective = cap.permitted = (1 << CAP_SYS_BOOT);
304 cap.inheritable = 0;
305 capset(&header, &cap);
306 }
307 #endif
308
309 }
310