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9108f8d9 1/* $OpenBSD: uidswap.c,v 1.35 2006/08/03 03:34:42 deraadt Exp $ */
3c0ef626 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"
9108f8d9 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>
3c0ef626 25
26#include "log.h"
27#include "uidswap.h"
cdd66111 28#include "xmalloc.h"
3c0ef626 29
30/*
31 * Note: all these functions must work in all of the following cases:
32 * 1. euid=0, ruid=0
33 * 2. euid=0, ruid!=0
34 * 3. euid!=0, ruid!=0
35 * Additionally, they must work regardless of whether the system has
36 * POSIX saved uids or not.
37 */
38
39#if defined(_POSIX_SAVED_IDS) && !defined(BROKEN_SAVED_UIDS)
40/* Lets assume that posix saved ids also work with seteuid, even though that
41 is not part of the posix specification. */
42#define SAVED_IDS_WORK_WITH_SETEUID
43/* Saved effective uid. */
44static uid_t saved_euid = 0;
45static gid_t saved_egid = 0;
46#endif
47
48/* Saved effective uid. */
49static int privileged = 0;
50static int temporarily_use_uid_effective = 0;
cdd66111 51static gid_t *saved_egroups = NULL, *user_groups = NULL;
3c0ef626 52static int saved_egroupslen = -1, user_groupslen = -1;
53
54/*
55 * Temporarily changes to the given uid. If the effective user
56 * id is not root, this does nothing. This call cannot be nested.
57 */
58void
59temporarily_use_uid(struct passwd *pw)
60{
61 /* Save the current euid, and egroups. */
62#ifdef SAVED_IDS_WORK_WITH_SETEUID
63 saved_euid = geteuid();
64 saved_egid = getegid();
41b2f314 65 debug("temporarily_use_uid: %u/%u (e=%u/%u)",
66 (u_int)pw->pw_uid, (u_int)pw->pw_gid,
67 (u_int)saved_euid, (u_int)saved_egid);
996d5e62 68#ifndef HAVE_CYGWIN
3c0ef626 69 if (saved_euid != 0) {
70 privileged = 0;
71 return;
72 }
996d5e62 73#endif
3c0ef626 74#else
75 if (geteuid() != 0) {
76 privileged = 0;
77 return;
78 }
79#endif /* SAVED_IDS_WORK_WITH_SETEUID */
80
81 privileged = 1;
82 temporarily_use_uid_effective = 1;
cdd66111 83
84 saved_egroupslen = getgroups(0, NULL);
3c0ef626 85 if (saved_egroupslen < 0)
86 fatal("getgroups: %.100s", strerror(errno));
cdd66111 87 if (saved_egroupslen > 0) {
88 saved_egroups = xrealloc(saved_egroups,
9108f8d9 89 saved_egroupslen, sizeof(gid_t));
cdd66111 90 if (getgroups(saved_egroupslen, saved_egroups) < 0)
91 fatal("getgroups: %.100s", strerror(errno));
92 } else { /* saved_egroupslen == 0 */
93 if (saved_egroups != NULL)
94 xfree(saved_egroups);
95 }
3c0ef626 96
97 /* set and save the user's groups */
98 if (user_groupslen == -1) {
99 if (initgroups(pw->pw_name, pw->pw_gid) < 0)
100 fatal("initgroups: %s: %.100s", pw->pw_name,
101 strerror(errno));
cdd66111 102
103 user_groupslen = getgroups(0, NULL);
3c0ef626 104 if (user_groupslen < 0)
105 fatal("getgroups: %.100s", strerror(errno));
cdd66111 106 if (user_groupslen > 0) {
107 user_groups = xrealloc(user_groups,
9108f8d9 108 user_groupslen, sizeof(gid_t));
cdd66111 109 if (getgroups(user_groupslen, user_groups) < 0)
110 fatal("getgroups: %.100s", strerror(errno));
111 } else { /* user_groupslen == 0 */
112 if (user_groups)
113 xfree(user_groups);
114 }
3c0ef626 115 }
3c0ef626 116 /* Set the effective uid to the given (unprivileged) uid. */
117 if (setgroups(user_groupslen, user_groups) < 0)
118 fatal("setgroups: %.100s", strerror(errno));
3c0ef626 119#ifndef SAVED_IDS_WORK_WITH_SETEUID
120 /* Propagate the privileged gid to all of our gids. */
121 if (setgid(getegid()) < 0)
122 debug("setgid %u: %.100s", (u_int) getegid(), strerror(errno));
123 /* Propagate the privileged uid to all of our uids. */
124 if (setuid(geteuid()) < 0)
125 debug("setuid %u: %.100s", (u_int) geteuid(), strerror(errno));
126#endif /* SAVED_IDS_WORK_WITH_SETEUID */
127 if (setegid(pw->pw_gid) < 0)
f5799ae1 128 fatal("setegid %u: %.100s", (u_int)pw->pw_gid,
3c0ef626 129 strerror(errno));
130 if (seteuid(pw->pw_uid) == -1)
f5799ae1 131 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid,
3c0ef626 132 strerror(errno));
133}
134
9108f8d9 135void
136permanently_drop_suid(uid_t uid)
137{
138 uid_t old_uid = getuid();
139
140 debug("permanently_drop_suid: %u", (u_int)uid);
141#if defined(HAVE_SETRESUID) && !defined(BROKEN_SETRESUID)
142 if (setresuid(uid, uid, uid) < 0)
143 fatal("setresuid %u: %.100s", (u_int)uid, strerror(errno));
144#elif defined(HAVE_SETREUID) && !defined(BROKEN_SETREUID)
145 if (setreuid(uid, uid) < 0)
146 fatal("setreuid %u: %.100s", (u_int)uid, strerror(errno));
147#else
148# ifndef SETEUID_BREAKS_SETUID
149 if (seteuid(uid) < 0)
150 fatal("seteuid %u: %.100s", (u_int)uid, strerror(errno));
151# endif
152 if (setuid(uid) < 0)
153 fatal("setuid %u: %.100s", (u_int)uid, strerror(errno));
154#endif
155
156#ifndef HAVE_CYGWIN
157 /* Try restoration of UID if changed (test clearing of saved uid) */
158 if (old_uid != uid &&
159 (setuid(old_uid) != -1 || seteuid(old_uid) != -1))
160 fatal("%s: was able to restore old [e]uid", __func__);
161#endif
162
163 /* Verify UID drop was successful */
164 if (getuid() != uid || geteuid() != uid) {
165 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)",
166 __func__, (u_int)getuid(), (u_int)geteuid(), (u_int)uid);
167 }
168}
169
3c0ef626 170/*
171 * Restores to the original (privileged) uid.
172 */
173void
174restore_uid(void)
175{
3c0ef626 176 /* it's a no-op unless privileged */
41b2f314 177 if (!privileged) {
178 debug("restore_uid: (unprivileged)");
3c0ef626 179 return;
41b2f314 180 }
3c0ef626 181 if (!temporarily_use_uid_effective)
182 fatal("restore_uid: temporarily_use_uid not effective");
183
184#ifdef SAVED_IDS_WORK_WITH_SETEUID
41b2f314 185 debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid);
3c0ef626 186 /* Set the effective uid back to the saved privileged uid. */
187 if (seteuid(saved_euid) < 0)
f5799ae1 188 fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno));
3c0ef626 189 if (setegid(saved_egid) < 0)
f5799ae1 190 fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno));
3c0ef626 191#else /* SAVED_IDS_WORK_WITH_SETEUID */
192 /*
193 * We are unable to restore the real uid to its unprivileged value.
194 * Propagate the real uid (usually more privileged) to effective uid
195 * as well.
196 */
197 setuid(getuid());
198 setgid(getgid());
199#endif /* SAVED_IDS_WORK_WITH_SETEUID */
200
3c0ef626 201 if (setgroups(saved_egroupslen, saved_egroups) < 0)
202 fatal("setgroups: %.100s", strerror(errno));
3c0ef626 203 temporarily_use_uid_effective = 0;
204}
205
206/*
207 * Permanently sets all uids to the given uid. This cannot be
208 * called while temporarily_use_uid is effective.
209 */
210void
211permanently_set_uid(struct passwd *pw)
212{
0fff78ff 213 uid_t old_uid = getuid();
214 gid_t old_gid = getgid();
215
9108f8d9 216 if (pw == NULL)
217 fatal("permanently_set_uid: no user given");
3c0ef626 218 if (temporarily_use_uid_effective)
f5799ae1 219 fatal("permanently_set_uid: temporarily_use_uid effective");
41b2f314 220 debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid,
221 (u_int)pw->pw_gid);
0fff78ff 222
cdd66111 223#if defined(HAVE_SETRESGID) && !defined(BROKEN_SETRESGID)
0fff78ff 224 if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) < 0)
225 fatal("setresgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
226#elif defined(HAVE_SETREGID) && !defined(BROKEN_SETREGID)
227 if (setregid(pw->pw_gid, pw->pw_gid) < 0)
228 fatal("setregid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
229#else
230 if (setegid(pw->pw_gid) < 0)
231 fatal("setegid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
3c0ef626 232 if (setgid(pw->pw_gid) < 0)
f5799ae1 233 fatal("setgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
0fff78ff 234#endif
235
91d9cdd3 236#ifdef __APPLE__
237 /*
238 * OS X requires initgroups after setgid to opt back into
239 * memberd support for >16 supplemental groups.
240 */
241 if (initgroups(pw->pw_name, pw->pw_gid) < 0)
242 fatal("initgroups %.100s %u: %.100s",
243 pw->pw_name, (u_int)pw->pw_gid, strerror(errno));
244#endif
245
cdd66111 246#if defined(HAVE_SETRESUID) && !defined(BROKEN_SETRESUID)
0fff78ff 247 if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) < 0)
248 fatal("setresuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
249#elif defined(HAVE_SETREUID) && !defined(BROKEN_SETREUID)
250 if (setreuid(pw->pw_uid, pw->pw_uid) < 0)
251 fatal("setreuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
252#else
253# ifndef SETEUID_BREAKS_SETUID
254 if (seteuid(pw->pw_uid) < 0)
255 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
256# endif
3c0ef626 257 if (setuid(pw->pw_uid) < 0)
f5799ae1 258 fatal("setuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
0fff78ff 259#endif
260
996d5e62 261#ifndef HAVE_CYGWIN
0fff78ff 262 /* Try restoration of GID if changed (test clearing of saved gid) */
996d5e62 263 if (old_gid != pw->pw_gid && pw->pw_uid != 0 &&
0fff78ff 264 (setgid(old_gid) != -1 || setegid(old_gid) != -1))
265 fatal("%s: was able to restore old [e]gid", __func__);
996d5e62 266#endif
0fff78ff 267
268 /* Verify GID drop was successful */
269 if (getgid() != pw->pw_gid || getegid() != pw->pw_gid) {
cdd66111 270 fatal("%s: egid incorrect gid:%u egid:%u (should be %u)",
271 __func__, (u_int)getgid(), (u_int)getegid(),
0fff78ff 272 (u_int)pw->pw_gid);
273 }
274
acc3d05e 275#ifndef HAVE_CYGWIN
0fff78ff 276 /* Try restoration of UID if changed (test clearing of saved uid) */
cdd66111 277 if (old_uid != pw->pw_uid &&
0fff78ff 278 (setuid(old_uid) != -1 || seteuid(old_uid) != -1))
279 fatal("%s: was able to restore old [e]uid", __func__);
acc3d05e 280#endif
0fff78ff 281
282 /* Verify UID drop was successful */
283 if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid) {
cdd66111 284 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)",
285 __func__, (u_int)getuid(), (u_int)geteuid(),
0fff78ff 286 (u_int)pw->pw_uid);
287 }
3c0ef626 288}
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