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. */
51static uid_t 	saved_euid = 0;
52static gid_t	saved_egid = 0;
53#endif
54
55/* Saved effective uid. */
56static int	privileged = 0;
57static int	temporarily_use_uid_effective = 0;
58static gid_t	*saved_egroups = NULL, *user_groups = NULL;
59static 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 */
65void
66temporarily_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
140void
141permanently_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 */
168void
169restore_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 */
205void
206permanently_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