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dtucker@openbsd.org882f8bf2015-06-24 01:49:19 +00001/* $OpenBSD: uidswap.c,v 1.39 2015/06/24 01:49:19 dtucker Exp $ */
Damien Millerd4a8b7e1999-10-27 13:42:43 +10002/*
Damien Miller95def091999-11-25 00:26:21 +11003 * Author: Tatu Ylonen <ylo@cs.hut.fi>
4 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5 * All rights reserved
Damien Miller95def091999-11-25 00:26:21 +11006 * Code for uid-swapping.
Damien Millere4340be2000-09-16 13:29:08 +11007 *
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".
Damien Miller95def091999-11-25 00:26:21 +110013 */
Damien Millerd4a8b7e1999-10-27 13:42:43 +100014
15#include "includes.h"
Damien Millerd4a8b7e1999-10-27 13:42:43 +100016
Darren Tucker39972492006-07-12 22:22:46 +100017#include <errno.h>
Damien Miller9f2abc42006-07-10 20:53:08 +100018#include <pwd.h>
Damien Millere3476ed2006-07-24 14:13:33 +100019#include <string.h>
Damien Millere6b3b612006-07-24 14:01:23 +100020#include <unistd.h>
deraadt@openbsd.org2ae4f332015-01-16 06:40:12 +000021#include <limits.h>
Damien Millerd7834352006-08-05 12:39:39 +100022#include <stdarg.h>
Damien Miller0600c702013-11-21 13:55:43 +110023#include <stdlib.h>
Damien Miller9f2abc42006-07-10 20:53:08 +100024
Damien Miller427a1d52006-07-10 20:20:33 +100025#include <grp.h>
26
Ben Lindstrom226cfa02001-01-22 05:34:40 +000027#include "log.h"
Damien Millerd4a8b7e1999-10-27 13:42:43 +100028#include "uidswap.h"
Damien Millera811d9a2004-02-24 13:05:11 +110029#include "xmalloc.h"
Damien Millerd4a8b7e1999-10-27 13:42:43 +100030
Damien Miller95def091999-11-25 00:26:21 +110031/*
32 * Note: all these functions must work in all of the following cases:
33 * 1. euid=0, ruid=0
34 * 2. euid=0, ruid!=0
35 * 3. euid!=0, ruid!=0
36 * Additionally, they must work regardless of whether the system has
37 * POSIX saved uids or not.
38 */
Damien Millerd4a8b7e1999-10-27 13:42:43 +100039
Ben Lindstrom4468b262001-04-26 23:03:37 +000040#if defined(_POSIX_SAVED_IDS) && !defined(BROKEN_SAVED_UIDS)
Damien Millerd4a8b7e1999-10-27 13:42:43 +100041/* Lets assume that posix saved ids also work with seteuid, even though that
42 is not part of the posix specification. */
Ben Lindstrom4468b262001-04-26 23:03:37 +000043#define SAVED_IDS_WORK_WITH_SETEUID
44/* Saved effective uid. */
45static uid_t saved_euid = 0;
46static gid_t saved_egid = 0;
47#endif
Ben Lindstrom768f9752001-04-25 06:27:11 +000048
Damien Millerd4a8b7e1999-10-27 13:42:43 +100049/* Saved effective uid. */
Ben Lindstrom3fcf1a22001-04-08 18:26:59 +000050static int privileged = 0;
51static int temporarily_use_uid_effective = 0;
Damien Millera811d9a2004-02-24 13:05:11 +110052static gid_t *saved_egroups = NULL, *user_groups = NULL;
Ben Lindstrom3fcf1a22001-04-08 18:26:59 +000053static int saved_egroupslen = -1, user_groupslen = -1;
Ben Lindstrom768f9752001-04-25 06:27:11 +000054
Damien Miller95def091999-11-25 00:26:21 +110055/*
56 * Temporarily changes to the given uid. If the effective user
57 * id is not root, this does nothing. This call cannot be nested.
58 */
Damien Miller4af51302000-04-16 11:18:38 +100059void
Ben Lindstrom3fcf1a22001-04-08 18:26:59 +000060temporarily_use_uid(struct passwd *pw)
Damien Millerd4a8b7e1999-10-27 13:42:43 +100061{
Ben Lindstrom768f9752001-04-25 06:27:11 +000062 /* Save the current euid, and egroups. */
Ben Lindstrom4468b262001-04-26 23:03:37 +000063#ifdef SAVED_IDS_WORK_WITH_SETEUID
Ben Lindstrom768f9752001-04-25 06:27:11 +000064 saved_euid = geteuid();
Ben Lindstrom4468b262001-04-26 23:03:37 +000065 saved_egid = getegid();
Ben Lindstrom1fa330c2002-07-23 21:29:49 +000066 debug("temporarily_use_uid: %u/%u (e=%u/%u)",
67 (u_int)pw->pw_uid, (u_int)pw->pw_gid,
68 (u_int)saved_euid, (u_int)saved_egid);
Darren Tucker2ea9b182005-02-22 17:57:13 +110069#ifndef HAVE_CYGWIN
Ben Lindstrom768f9752001-04-25 06:27:11 +000070 if (saved_euid != 0) {
71 privileged = 0;
72 return;
73 }
Darren Tucker2ea9b182005-02-22 17:57:13 +110074#endif
Ben Lindstrom4468b262001-04-26 23:03:37 +000075#else
76 if (geteuid() != 0) {
77 privileged = 0;
78 return;
79 }
80#endif /* SAVED_IDS_WORK_WITH_SETEUID */
81
Ben Lindstrom768f9752001-04-25 06:27:11 +000082 privileged = 1;
83 temporarily_use_uid_effective = 1;
Damien Millera811d9a2004-02-24 13:05:11 +110084
85 saved_egroupslen = getgroups(0, NULL);
Ben Lindstrom768f9752001-04-25 06:27:11 +000086 if (saved_egroupslen < 0)
87 fatal("getgroups: %.100s", strerror(errno));
Damien Millera811d9a2004-02-24 13:05:11 +110088 if (saved_egroupslen > 0) {
Darren Tuckerd1680d32015-04-30 09:18:11 +100089 saved_egroups = xreallocarray(saved_egroups,
Damien Miller36812092006-03-26 14:22:47 +110090 saved_egroupslen, sizeof(gid_t));
Damien Millera811d9a2004-02-24 13:05:11 +110091 if (getgroups(saved_egroupslen, saved_egroups) < 0)
92 fatal("getgroups: %.100s", strerror(errno));
93 } else { /* saved_egroupslen == 0 */
Darren Tuckerf60845f2013-06-02 08:07:31 +100094 free(saved_egroups);
Damien Millera811d9a2004-02-24 13:05:11 +110095 }
Ben Lindstrom768f9752001-04-25 06:27:11 +000096
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));
Damien Millera811d9a2004-02-24 13:05:11 +1100102
103 user_groupslen = getgroups(0, NULL);
Ben Lindstrom768f9752001-04-25 06:27:11 +0000104 if (user_groupslen < 0)
105 fatal("getgroups: %.100s", strerror(errno));
Damien Millera811d9a2004-02-24 13:05:11 +1100106 if (user_groupslen > 0) {
Darren Tuckerd1680d32015-04-30 09:18:11 +1000107 user_groups = xreallocarray(user_groups,
Damien Miller36812092006-03-26 14:22:47 +1100108 user_groupslen, sizeof(gid_t));
Damien Millera811d9a2004-02-24 13:05:11 +1100109 if (getgroups(user_groupslen, user_groups) < 0)
110 fatal("getgroups: %.100s", strerror(errno));
111 } else { /* user_groupslen == 0 */
Darren Tuckerf60845f2013-06-02 08:07:31 +1000112 free(user_groups);
Damien Millera811d9a2004-02-24 13:05:11 +1100113 }
Ben Lindstrom768f9752001-04-25 06:27:11 +0000114 }
115 /* Set the effective uid to the given (unprivileged) uid. */
dtucker@openbsd.org882f8bf2015-06-24 01:49:19 +0000116 if (setgroups(user_groupslen, user_groups) < 0)
Ben Lindstrom3fcf1a22001-04-08 18:26:59 +0000117 fatal("setgroups: %.100s", strerror(errno));
Ben Lindstrom4468b262001-04-26 23:03:37 +0000118#ifndef SAVED_IDS_WORK_WITH_SETEUID
119 /* Propagate the privileged gid to all of our gids. */
120 if (setgid(getegid()) < 0)
121 debug("setgid %u: %.100s", (u_int) getegid(), strerror(errno));
122 /* Propagate the privileged uid to all of our uids. */
123 if (setuid(geteuid()) < 0)
124 debug("setuid %u: %.100s", (u_int) geteuid(), strerror(errno));
125#endif /* SAVED_IDS_WORK_WITH_SETEUID */
Ben Lindstromf52373f2001-04-08 18:38:04 +0000126 if (setegid(pw->pw_gid) < 0)
Ben Lindstromabff1dd2002-06-06 20:38:49 +0000127 fatal("setegid %u: %.100s", (u_int)pw->pw_gid,
Ben Lindstrom768f9752001-04-25 06:27:11 +0000128 strerror(errno));
129 if (seteuid(pw->pw_uid) == -1)
Ben Lindstromabff1dd2002-06-06 20:38:49 +0000130 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid,
Ben Lindstrom768f9752001-04-25 06:27:11 +0000131 strerror(errno));
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000132}
Ben Lindstrom768f9752001-04-25 06:27:11 +0000133
Damien Miller2e5fe882006-06-13 13:10:00 +1000134void
135permanently_drop_suid(uid_t uid)
136{
Darren Tucker89c532d2014-01-18 20:43:49 +1100137#ifndef HAVE_CYGWIN
Damien Miller2e5fe882006-06-13 13:10:00 +1000138 uid_t old_uid = getuid();
Darren Tucker89c532d2014-01-18 20:43:49 +1100139#endif
Damien Miller2e5fe882006-06-13 13:10:00 +1000140
141 debug("permanently_drop_suid: %u", (u_int)uid);
Damien Miller2e5fe882006-06-13 13:10:00 +1000142 if (setresuid(uid, uid, uid) < 0)
143 fatal("setresuid %u: %.100s", (u_int)uid, strerror(errno));
Damien Miller2e5fe882006-06-13 13:10:00 +1000144
145#ifndef HAVE_CYGWIN
146 /* Try restoration of UID if changed (test clearing of saved uid) */
147 if (old_uid != uid &&
148 (setuid(old_uid) != -1 || seteuid(old_uid) != -1))
149 fatal("%s: was able to restore old [e]uid", __func__);
150#endif
151
152 /* Verify UID drop was successful */
153 if (getuid() != uid || geteuid() != uid) {
154 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)",
155 __func__, (u_int)getuid(), (u_int)geteuid(), (u_int)uid);
156 }
157}
158
Damien Miller95def091999-11-25 00:26:21 +1100159/*
Ben Lindstromee2786a2001-04-22 17:08:00 +0000160 * Restores to the original (privileged) uid.
Damien Miller95def091999-11-25 00:26:21 +1100161 */
Damien Miller4af51302000-04-16 11:18:38 +1000162void
Ben Lindstrom46c16222000-12-22 01:43:59 +0000163restore_uid(void)
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000164{
Ben Lindstrom3fcf1a22001-04-08 18:26:59 +0000165 /* it's a no-op unless privileged */
Ben Lindstrom1fa330c2002-07-23 21:29:49 +0000166 if (!privileged) {
167 debug("restore_uid: (unprivileged)");
Ben Lindstrom3fcf1a22001-04-08 18:26:59 +0000168 return;
Ben Lindstrom1fa330c2002-07-23 21:29:49 +0000169 }
Ben Lindstrom3fcf1a22001-04-08 18:26:59 +0000170 if (!temporarily_use_uid_effective)
171 fatal("restore_uid: temporarily_use_uid not effective");
Ben Lindstrom4468b262001-04-26 23:03:37 +0000172
173#ifdef SAVED_IDS_WORK_WITH_SETEUID
Ben Lindstrom18d2b5d2002-07-30 19:32:07 +0000174 debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid);
Ben Lindstromee2786a2001-04-22 17:08:00 +0000175 /* Set the effective uid back to the saved privileged uid. */
Damien Miller95def091999-11-25 00:26:21 +1100176 if (seteuid(saved_euid) < 0)
Ben Lindstromabff1dd2002-06-06 20:38:49 +0000177 fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno));
Ben Lindstrom4468b262001-04-26 23:03:37 +0000178 if (setegid(saved_egid) < 0)
Ben Lindstromabff1dd2002-06-06 20:38:49 +0000179 fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno));
Ben Lindstrom4468b262001-04-26 23:03:37 +0000180#else /* SAVED_IDS_WORK_WITH_SETEUID */
181 /*
182 * We are unable to restore the real uid to its unprivileged value.
183 * Propagate the real uid (usually more privileged) to effective uid
184 * as well.
185 */
186 setuid(getuid());
187 setgid(getgid());
188#endif /* SAVED_IDS_WORK_WITH_SETEUID */
189
dtucker@openbsd.org7ed01a92015-06-24 01:49:19 +0000190 if (setgroups(saved_egroupslen, saved_egroups) < 0)
Ben Lindstrom3fcf1a22001-04-08 18:26:59 +0000191 fatal("setgroups: %.100s", strerror(errno));
Ben Lindstrom3fcf1a22001-04-08 18:26:59 +0000192 temporarily_use_uid_effective = 0;
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000193}
194
Damien Miller95def091999-11-25 00:26:21 +1100195/*
196 * Permanently sets all uids to the given uid. This cannot be
197 * called while temporarily_use_uid is effective.
198 */
Damien Miller4af51302000-04-16 11:18:38 +1000199void
Ben Lindstrom3fcf1a22001-04-08 18:26:59 +0000200permanently_set_uid(struct passwd *pw)
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000201{
Darren Tucker89c532d2014-01-18 20:43:49 +1100202#ifndef HAVE_CYGWIN
Damien Miller5fe46a42003-06-05 09:53:31 +1000203 uid_t old_uid = getuid();
204 gid_t old_gid = getgid();
Darren Tucker89c532d2014-01-18 20:43:49 +1100205#endif
Damien Miller5fe46a42003-06-05 09:53:31 +1000206
Damien Miller6b4069a2006-06-13 13:05:15 +1000207 if (pw == NULL)
208 fatal("permanently_set_uid: no user given");
Ben Lindstrom3fcf1a22001-04-08 18:26:59 +0000209 if (temporarily_use_uid_effective)
Ben Lindstromca8943e2002-06-06 20:42:04 +0000210 fatal("permanently_set_uid: temporarily_use_uid effective");
Ben Lindstrom1fa330c2002-07-23 21:29:49 +0000211 debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid,
212 (u_int)pw->pw_gid);
Damien Miller5fe46a42003-06-05 09:53:31 +1000213
Damien Miller5fe46a42003-06-05 09:53:31 +1000214 if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) < 0)
215 fatal("setresgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
Damien Miller5fe46a42003-06-05 09:53:31 +1000216
Damien Miller1598d6b2009-01-21 16:04:24 +1100217#ifdef __APPLE__
218 /*
219 * OS X requires initgroups after setgid to opt back into
220 * memberd support for >16 supplemental groups.
221 */
222 if (initgroups(pw->pw_name, pw->pw_gid) < 0)
223 fatal("initgroups %.100s %u: %.100s",
224 pw->pw_name, (u_int)pw->pw_gid, strerror(errno));
225#endif
226
Damien Miller5fe46a42003-06-05 09:53:31 +1000227 if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) < 0)
228 fatal("setresuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
Damien Miller5fe46a42003-06-05 09:53:31 +1000229
Darren Tucker35beadd2004-10-19 16:33:33 +1000230#ifndef HAVE_CYGWIN
Damien Miller5fe46a42003-06-05 09:53:31 +1000231 /* Try restoration of GID if changed (test clearing of saved gid) */
Darren Tucker35beadd2004-10-19 16:33:33 +1000232 if (old_gid != pw->pw_gid && pw->pw_uid != 0 &&
Damien Miller5fe46a42003-06-05 09:53:31 +1000233 (setgid(old_gid) != -1 || setegid(old_gid) != -1))
Darren Tucker400b8782003-06-06 10:46:04 +1000234 fatal("%s: was able to restore old [e]gid", __func__);
Darren Tucker35beadd2004-10-19 16:33:33 +1000235#endif
Damien Miller5fe46a42003-06-05 09:53:31 +1000236
237 /* Verify GID drop was successful */
238 if (getgid() != pw->pw_gid || getegid() != pw->pw_gid) {
Damien Millera8e06ce2003-11-21 23:48:55 +1100239 fatal("%s: egid incorrect gid:%u egid:%u (should be %u)",
240 __func__, (u_int)getgid(), (u_int)getegid(),
Damien Miller5fe46a42003-06-05 09:53:31 +1000241 (u_int)pw->pw_gid);
242 }
243
Darren Tuckerfbe3b362003-09-22 12:54:37 +1000244#ifndef HAVE_CYGWIN
Damien Miller5fe46a42003-06-05 09:53:31 +1000245 /* Try restoration of UID if changed (test clearing of saved uid) */
Damien Millera8e06ce2003-11-21 23:48:55 +1100246 if (old_uid != pw->pw_uid &&
Damien Miller5fe46a42003-06-05 09:53:31 +1000247 (setuid(old_uid) != -1 || seteuid(old_uid) != -1))
Darren Tucker400b8782003-06-06 10:46:04 +1000248 fatal("%s: was able to restore old [e]uid", __func__);
Darren Tuckerfbe3b362003-09-22 12:54:37 +1000249#endif
Damien Miller5fe46a42003-06-05 09:53:31 +1000250
251 /* Verify UID drop was successful */
252 if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid) {
Damien Millera8e06ce2003-11-21 23:48:55 +1100253 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)",
254 __func__, (u_int)getuid(), (u_int)geteuid(),
Damien Miller5fe46a42003-06-05 09:53:31 +1000255 (u_int)pw->pw_uid);
256 }
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000257}