1 /* $OpenBSD: uidswap.c,v 1.35 2006/08/03 03:34:42 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 <sys/param.h>
18 #include <errno.h>
19 #include <pwd.h>
20 #include <string.h>
21 #include <unistd.h>
22 #include <stdarg.h>
23
24 #include <grp.h>
25
26 #include "log.h"
27 #include "uidswap.h"
28 #include "xmalloc.h"
29
30 #ifdef ANDROID
31 #include <private/android_filesystem_config.h>
32 #include <linux/capability.h>
33 #include <linux/prctl.h>
34 #endif
35
36 /*
37 * Note: all these functions must work in all of the following cases:
38 * 1. euid=0, ruid=0
39 * 2. euid=0, ruid!=0
40 * 3. euid!=0, ruid!=0
41 * Additionally, they must work regardless of whether the system has
42 * POSIX saved uids or not.
43 */
44
45 #if defined(_POSIX_SAVED_IDS) && !defined(BROKEN_SAVED_UIDS)
46 /* Lets assume that posix saved ids also work with seteuid, even though that
47 is not part of the posix specification. */
48 #define SAVED_IDS_WORK_WITH_SETEUID
49 /* Saved effective uid. */
50 static uid_t saved_euid = 0;
51 static gid_t saved_egid = 0;
52 #endif
53
54 /* Saved effective uid. */
55 static int privileged = 0;
56 static int temporarily_use_uid_effective = 0;
57 static gid_t *saved_egroups = NULL, *user_groups = NULL;
58 static int saved_egroupslen = -1, user_groupslen = -1;
59
60 /*
61 * Temporarily changes to the given uid. If the effective user
62 * id is not root, this does nothing. This call cannot be nested.
63 */
64 void
temporarily_use_uid(struct passwd * pw)65 temporarily_use_uid(struct passwd *pw)
66 {
67 /* Save the current euid, and egroups. */
68 #ifdef SAVED_IDS_WORK_WITH_SETEUID
69 saved_euid = geteuid();
70 saved_egid = getegid();
71 debug("temporarily_use_uid: %u/%u (e=%u/%u)",
72 (u_int)pw->pw_uid, (u_int)pw->pw_gid,
73 (u_int)saved_euid, (u_int)saved_egid);
74 #ifndef HAVE_CYGWIN
75 if (saved_euid != 0) {
76 privileged = 0;
77 return;
78 }
79 #endif
80 #else
81 if (geteuid() != 0) {
82 privileged = 0;
83 return;
84 }
85 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
86
87 privileged = 1;
88 temporarily_use_uid_effective = 1;
89
90 saved_egroupslen = getgroups(0, NULL);
91 if (saved_egroupslen < 0)
92 fatal("getgroups: %.100s", strerror(errno));
93 if (saved_egroupslen > 0) {
94 saved_egroups = xrealloc(saved_egroups,
95 saved_egroupslen, sizeof(gid_t));
96 if (getgroups(saved_egroupslen, saved_egroups) < 0)
97 fatal("getgroups: %.100s", strerror(errno));
98 } else { /* saved_egroupslen == 0 */
99 if (saved_egroups != NULL)
100 xfree(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 if (user_groups)
119 xfree(user_groups);
120 }
121 }
122 /* Set the effective uid to the given (unprivileged) uid. */
123 if (setgroups(user_groupslen, user_groups) < 0)
124 fatal("setgroups: %.100s", strerror(errno));
125 #ifndef SAVED_IDS_WORK_WITH_SETEUID
126 /* Propagate the privileged gid to all of our gids. */
127 if (setgid(getegid()) < 0)
128 debug("setgid %u: %.100s", (u_int) getegid(), strerror(errno));
129 /* Propagate the privileged uid to all of our uids. */
130 if (setuid(geteuid()) < 0)
131 debug("setuid %u: %.100s", (u_int) geteuid(), strerror(errno));
132 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
133 if (setegid(pw->pw_gid) < 0)
134 fatal("setegid %u: %.100s", (u_int)pw->pw_gid,
135 strerror(errno));
136 if (seteuid(pw->pw_uid) == -1)
137 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid,
138 strerror(errno));
139 }
140
141 void
permanently_drop_suid(uid_t uid)142 permanently_drop_suid(uid_t uid)
143 {
144 uid_t old_uid = getuid();
145
146 debug("permanently_drop_suid: %u", (u_int)uid);
147 #if defined(HAVE_SETRESUID) && !defined(BROKEN_SETRESUID)
148 if (setresuid(uid, uid, uid) < 0)
149 fatal("setresuid %u: %.100s", (u_int)uid, strerror(errno));
150 #elif defined(HAVE_SETREUID) && !defined(BROKEN_SETREUID)
151 if (setreuid(uid, uid) < 0)
152 fatal("setreuid %u: %.100s", (u_int)uid, strerror(errno));
153 #else
154 # ifndef SETEUID_BREAKS_SETUID
155 if (seteuid(uid) < 0)
156 fatal("seteuid %u: %.100s", (u_int)uid, strerror(errno));
157 # endif
158 if (setuid(uid) < 0)
159 fatal("setuid %u: %.100s", (u_int)uid, strerror(errno));
160 #endif
161
162 #ifndef HAVE_CYGWIN
163 /* Try restoration of UID if changed (test clearing of saved uid) */
164 if (old_uid != uid &&
165 (setuid(old_uid) != -1 || seteuid(old_uid) != -1))
166 fatal("%s: was able to restore old [e]uid", __func__);
167 #endif
168
169 /* Verify UID drop was successful */
170 if (getuid() != uid || geteuid() != uid) {
171 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)",
172 __func__, (u_int)getuid(), (u_int)geteuid(), (u_int)uid);
173 }
174 }
175
176 /*
177 * Restores to the original (privileged) uid.
178 */
179 void
restore_uid(void)180 restore_uid(void)
181 {
182 /* it's a no-op unless privileged */
183 if (!privileged) {
184 debug("restore_uid: (unprivileged)");
185 return;
186 }
187 if (!temporarily_use_uid_effective)
188 fatal("restore_uid: temporarily_use_uid not effective");
189
190 #ifdef SAVED_IDS_WORK_WITH_SETEUID
191 debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid);
192 /* Set the effective uid back to the saved privileged uid. */
193 if (seteuid(saved_euid) < 0)
194 fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno));
195 if (setegid(saved_egid) < 0)
196 fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno));
197 #else /* SAVED_IDS_WORK_WITH_SETEUID */
198 /*
199 * We are unable to restore the real uid to its unprivileged value.
200 * Propagate the real uid (usually more privileged) to effective uid
201 * as well.
202 */
203 setuid(getuid());
204 setgid(getgid());
205 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
206
207 if (setgroups(saved_egroupslen, saved_egroups) < 0)
208 fatal("setgroups: %.100s", strerror(errno));
209 temporarily_use_uid_effective = 0;
210 }
211
212 /*
213 * Permanently sets all uids to the given uid. This cannot be
214 * called while temporarily_use_uid is effective.
215 */
216 void
permanently_set_uid(struct passwd * pw)217 permanently_set_uid(struct passwd *pw)
218 {
219 uid_t old_uid = getuid();
220 gid_t old_gid = getgid();
221 #ifdef ANDROID
222 struct __user_cap_header_struct header;
223 struct __user_cap_data_struct cap;
224 #endif
225
226 if (pw == NULL)
227 fatal("permanently_set_uid: no user given");
228 if (temporarily_use_uid_effective)
229 fatal("permanently_set_uid: temporarily_use_uid effective");
230 debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid,
231 (u_int)pw->pw_gid);
232
233 #ifdef ANDROID
234 if (pw->pw_uid == AID_SHELL) {
235 prctl(PR_SET_KEEPCAPS, 1, 0, 0, 0);
236
237 /* add extra groups needed for shell user:
238 ** AID_LOG to read system logs (adb logcat)
239 ** AID_INPUT to diagnose input issues (getevent)
240 ** AID_INET to diagnose network issues (netcfg, ping)
241 ** AID_GRAPHICS to access the frame buffer
242 ** AID_NET_BT and AID_NET_BT_ADMIN to diagnose bluetooth (hcidump)
243 ** AID_SDCARD_RW to allow writing to the SD card
244 ** AID_MOUNT to allow unmounting the SD card before rebooting
245 ** AID_NET_BW_STATS to read out qtaguid statistics
246 */
247 gid_t groups[] = { AID_LOG, AID_INPUT, AID_INET, AID_GRAPHICS,
248 AID_NET_BT, AID_NET_BT_ADMIN, AID_SDCARD_RW,
249 AID_MOUNT, AID_NET_BW_STATS };
250 setgroups(sizeof(groups)/sizeof(groups[0]), groups);
251 }
252 #endif
253
254 #if defined(HAVE_SETRESGID) && !defined(BROKEN_SETRESGID)
255 if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) < 0)
256 fatal("setresgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
257 #elif defined(HAVE_SETREGID) && !defined(BROKEN_SETREGID)
258 if (setregid(pw->pw_gid, pw->pw_gid) < 0)
259 fatal("setregid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
260 #else
261 if (setegid(pw->pw_gid) < 0)
262 fatal("setegid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
263 if (setgid(pw->pw_gid) < 0)
264 fatal("setgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
265 #endif
266
267 #ifdef __APPLE__
268 /*
269 * OS X requires initgroups after setgid to opt back into
270 * memberd support for >16 supplemental groups.
271 */
272 if (initgroups(pw->pw_name, pw->pw_gid) < 0)
273 fatal("initgroups %.100s %u: %.100s",
274 pw->pw_name, (u_int)pw->pw_gid, strerror(errno));
275 #endif
276
277 #if defined(HAVE_SETRESUID) && !defined(BROKEN_SETRESUID)
278 if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) < 0)
279 fatal("setresuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
280 #elif defined(HAVE_SETREUID) && !defined(BROKEN_SETREUID)
281 if (setreuid(pw->pw_uid, pw->pw_uid) < 0)
282 fatal("setreuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
283 #else
284 # ifndef SETEUID_BREAKS_SETUID
285 if (seteuid(pw->pw_uid) < 0)
286 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
287 # endif
288 if (setuid(pw->pw_uid) < 0)
289 fatal("setuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
290 #endif
291
292 #ifndef HAVE_CYGWIN
293 /* Try restoration of GID if changed (test clearing of saved gid) */
294 if (old_gid != pw->pw_gid && pw->pw_uid != 0 &&
295 (setgid(old_gid) != -1 || setegid(old_gid) != -1))
296 fatal("%s: was able to restore old [e]gid", __func__);
297 #endif
298
299 /* Verify GID drop was successful */
300 if (getgid() != pw->pw_gid || getegid() != pw->pw_gid) {
301 fatal("%s: egid incorrect gid:%u egid:%u (should be %u)",
302 __func__, (u_int)getgid(), (u_int)getegid(),
303 (u_int)pw->pw_gid);
304 }
305
306 #ifndef HAVE_CYGWIN
307 /* Try restoration of UID if changed (test clearing of saved uid) */
308 if (old_uid != pw->pw_uid &&
309 (setuid(old_uid) != -1 || seteuid(old_uid) != -1))
310 fatal("%s: was able to restore old [e]uid", __func__);
311 #endif
312
313 /* Verify UID drop was successful */
314 if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid) {
315 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)",
316 __func__, (u_int)getuid(), (u_int)geteuid(),
317 (u_int)pw->pw_uid);
318 }
319
320 #ifdef ANDROID
321 if (pw->pw_uid == AID_SHELL) {
322 /* set CAP_SYS_BOOT capability, so "adb reboot" will succeed */
323 header.version = _LINUX_CAPABILITY_VERSION;
324 header.pid = 0;
325 cap.effective = cap.permitted = (1 << CAP_SYS_BOOT);
326 cap.inheritable = 0;
327 capset(&header, &cap);
328 }
329 #endif
330
331 }
332