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deraadt@openbsd.org4d28fa72019-06-28 13:35:04 +00001/* $OpenBSD: uidswap.c,v 1.42 2019/06/28 13:35:04 deraadt 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;
djm@openbsd.org26f96ca2018-06-15 07:01:11 +000052static uid_t user_groups_uid;
Damien Millera811d9a2004-02-24 13:05:11 +110053static gid_t *saved_egroups = NULL, *user_groups = NULL;
Ben Lindstrom3fcf1a22001-04-08 18:26:59 +000054static int saved_egroupslen = -1, user_groupslen = -1;
Ben Lindstrom768f9752001-04-25 06:27:11 +000055
Damien Miller95def091999-11-25 00:26:21 +110056/*
57 * Temporarily changes to the given uid. If the effective user
58 * id is not root, this does nothing. This call cannot be nested.
59 */
Damien Miller4af51302000-04-16 11:18:38 +100060void
Ben Lindstrom3fcf1a22001-04-08 18:26:59 +000061temporarily_use_uid(struct passwd *pw)
Damien Millerd4a8b7e1999-10-27 13:42:43 +100062{
Ben Lindstrom768f9752001-04-25 06:27:11 +000063 /* Save the current euid, and egroups. */
Ben Lindstrom4468b262001-04-26 23:03:37 +000064#ifdef SAVED_IDS_WORK_WITH_SETEUID
Ben Lindstrom768f9752001-04-25 06:27:11 +000065 saved_euid = geteuid();
Ben Lindstrom4468b262001-04-26 23:03:37 +000066 saved_egid = getegid();
Ben Lindstrom1fa330c2002-07-23 21:29:49 +000067 debug("temporarily_use_uid: %u/%u (e=%u/%u)",
68 (u_int)pw->pw_uid, (u_int)pw->pw_gid,
69 (u_int)saved_euid, (u_int)saved_egid);
Darren Tucker2ea9b182005-02-22 17:57:13 +110070#ifndef HAVE_CYGWIN
Ben Lindstrom768f9752001-04-25 06:27:11 +000071 if (saved_euid != 0) {
72 privileged = 0;
73 return;
74 }
Darren Tucker2ea9b182005-02-22 17:57:13 +110075#endif
Ben Lindstrom4468b262001-04-26 23:03:37 +000076#else
77 if (geteuid() != 0) {
78 privileged = 0;
79 return;
80 }
81#endif /* SAVED_IDS_WORK_WITH_SETEUID */
82
Ben Lindstrom768f9752001-04-25 06:27:11 +000083 privileged = 1;
84 temporarily_use_uid_effective = 1;
Damien Millera811d9a2004-02-24 13:05:11 +110085
86 saved_egroupslen = getgroups(0, NULL);
deraadt@openbsd.org4d28fa72019-06-28 13:35:04 +000087 if (saved_egroupslen == -1)
Ben Lindstrom768f9752001-04-25 06:27:11 +000088 fatal("getgroups: %.100s", strerror(errno));
Damien Millera811d9a2004-02-24 13:05:11 +110089 if (saved_egroupslen > 0) {
Darren Tuckerd1680d32015-04-30 09:18:11 +100090 saved_egroups = xreallocarray(saved_egroups,
Damien Miller36812092006-03-26 14:22:47 +110091 saved_egroupslen, sizeof(gid_t));
deraadt@openbsd.org4d28fa72019-06-28 13:35:04 +000092 if (getgroups(saved_egroupslen, saved_egroups) == -1)
Damien Millera811d9a2004-02-24 13:05:11 +110093 fatal("getgroups: %.100s", strerror(errno));
94 } else { /* saved_egroupslen == 0 */
Darren Tuckerf60845f2013-06-02 08:07:31 +100095 free(saved_egroups);
djm@openbsd.org26f96ca2018-06-15 07:01:11 +000096 saved_egroups = NULL;
Damien Millera811d9a2004-02-24 13:05:11 +110097 }
Ben Lindstrom768f9752001-04-25 06:27:11 +000098
99 /* set and save the user's groups */
djm@openbsd.org26f96ca2018-06-15 07:01:11 +0000100 if (user_groupslen == -1 || user_groups_uid != pw->pw_uid) {
deraadt@openbsd.org4d28fa72019-06-28 13:35:04 +0000101 if (initgroups(pw->pw_name, pw->pw_gid) == -1)
Ben Lindstrom768f9752001-04-25 06:27:11 +0000102 fatal("initgroups: %s: %.100s", pw->pw_name,
103 strerror(errno));
Damien Millera811d9a2004-02-24 13:05:11 +1100104
105 user_groupslen = getgroups(0, NULL);
deraadt@openbsd.org4d28fa72019-06-28 13:35:04 +0000106 if (user_groupslen == -1)
Ben Lindstrom768f9752001-04-25 06:27:11 +0000107 fatal("getgroups: %.100s", strerror(errno));
Damien Millera811d9a2004-02-24 13:05:11 +1100108 if (user_groupslen > 0) {
Darren Tuckerd1680d32015-04-30 09:18:11 +1000109 user_groups = xreallocarray(user_groups,
Damien Miller36812092006-03-26 14:22:47 +1100110 user_groupslen, sizeof(gid_t));
deraadt@openbsd.org4d28fa72019-06-28 13:35:04 +0000111 if (getgroups(user_groupslen, user_groups) == -1)
Damien Millera811d9a2004-02-24 13:05:11 +1100112 fatal("getgroups: %.100s", strerror(errno));
113 } else { /* user_groupslen == 0 */
Darren Tuckerf60845f2013-06-02 08:07:31 +1000114 free(user_groups);
djm@openbsd.org26f96ca2018-06-15 07:01:11 +0000115 user_groups = NULL;
Damien Millera811d9a2004-02-24 13:05:11 +1100116 }
djm@openbsd.org26f96ca2018-06-15 07:01:11 +0000117 user_groups_uid = pw->pw_uid;
Ben Lindstrom768f9752001-04-25 06:27:11 +0000118 }
119 /* Set the effective uid to the given (unprivileged) uid. */
deraadt@openbsd.org4d28fa72019-06-28 13:35:04 +0000120 if (setgroups(user_groupslen, user_groups) == -1)
Ben Lindstrom3fcf1a22001-04-08 18:26:59 +0000121 fatal("setgroups: %.100s", strerror(errno));
Ben Lindstrom4468b262001-04-26 23:03:37 +0000122#ifndef SAVED_IDS_WORK_WITH_SETEUID
123 /* Propagate the privileged gid to all of our gids. */
deraadt@openbsd.org4d28fa72019-06-28 13:35:04 +0000124 if (setgid(getegid()) == -1)
Ben Lindstrom4468b262001-04-26 23:03:37 +0000125 debug("setgid %u: %.100s", (u_int) getegid(), strerror(errno));
126 /* Propagate the privileged uid to all of our uids. */
deraadt@openbsd.org4d28fa72019-06-28 13:35:04 +0000127 if (setuid(geteuid()) == -1)
Ben Lindstrom4468b262001-04-26 23:03:37 +0000128 debug("setuid %u: %.100s", (u_int) geteuid(), strerror(errno));
129#endif /* SAVED_IDS_WORK_WITH_SETEUID */
deraadt@openbsd.org4d28fa72019-06-28 13:35:04 +0000130 if (setegid(pw->pw_gid) == -1)
Ben Lindstromabff1dd2002-06-06 20:38:49 +0000131 fatal("setegid %u: %.100s", (u_int)pw->pw_gid,
Ben Lindstrom768f9752001-04-25 06:27:11 +0000132 strerror(errno));
133 if (seteuid(pw->pw_uid) == -1)
Ben Lindstromabff1dd2002-06-06 20:38:49 +0000134 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid,
Ben Lindstrom768f9752001-04-25 06:27:11 +0000135 strerror(errno));
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000136}
Ben Lindstrom768f9752001-04-25 06:27:11 +0000137
Damien Miller95def091999-11-25 00:26:21 +1100138/*
Ben Lindstromee2786a2001-04-22 17:08:00 +0000139 * Restores to the original (privileged) uid.
Damien Miller95def091999-11-25 00:26:21 +1100140 */
Damien Miller4af51302000-04-16 11:18:38 +1000141void
Ben Lindstrom46c16222000-12-22 01:43:59 +0000142restore_uid(void)
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000143{
Ben Lindstrom3fcf1a22001-04-08 18:26:59 +0000144 /* it's a no-op unless privileged */
Ben Lindstrom1fa330c2002-07-23 21:29:49 +0000145 if (!privileged) {
146 debug("restore_uid: (unprivileged)");
Ben Lindstrom3fcf1a22001-04-08 18:26:59 +0000147 return;
Ben Lindstrom1fa330c2002-07-23 21:29:49 +0000148 }
Ben Lindstrom3fcf1a22001-04-08 18:26:59 +0000149 if (!temporarily_use_uid_effective)
150 fatal("restore_uid: temporarily_use_uid not effective");
Ben Lindstrom4468b262001-04-26 23:03:37 +0000151
152#ifdef SAVED_IDS_WORK_WITH_SETEUID
Ben Lindstrom18d2b5d2002-07-30 19:32:07 +0000153 debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid);
Ben Lindstromee2786a2001-04-22 17:08:00 +0000154 /* Set the effective uid back to the saved privileged uid. */
deraadt@openbsd.org4d28fa72019-06-28 13:35:04 +0000155 if (seteuid(saved_euid) == -1)
Ben Lindstromabff1dd2002-06-06 20:38:49 +0000156 fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno));
deraadt@openbsd.org4d28fa72019-06-28 13:35:04 +0000157 if (setegid(saved_egid) == -1)
Ben Lindstromabff1dd2002-06-06 20:38:49 +0000158 fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno));
Ben Lindstrom4468b262001-04-26 23:03:37 +0000159#else /* SAVED_IDS_WORK_WITH_SETEUID */
160 /*
161 * We are unable to restore the real uid to its unprivileged value.
162 * Propagate the real uid (usually more privileged) to effective uid
163 * as well.
164 */
Damien Millerc17e4632019-09-13 13:12:42 +1000165 if (setuid(getuid()) == -1)
166 fatal("%s: setuid failed: %s", __func__, strerror(errno));
167 if (setgid(getgid()) == -1)
168 fatal("%s: setgid failed: %s", __func__, strerror(errno));
Ben Lindstrom4468b262001-04-26 23:03:37 +0000169#endif /* SAVED_IDS_WORK_WITH_SETEUID */
170
deraadt@openbsd.org4d28fa72019-06-28 13:35:04 +0000171 if (setgroups(saved_egroupslen, saved_egroups) == -1)
Ben Lindstrom3fcf1a22001-04-08 18:26:59 +0000172 fatal("setgroups: %.100s", strerror(errno));
Ben Lindstrom3fcf1a22001-04-08 18:26:59 +0000173 temporarily_use_uid_effective = 0;
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000174}
175
Damien Miller95def091999-11-25 00:26:21 +1100176/*
177 * Permanently sets all uids to the given uid. This cannot be
178 * called while temporarily_use_uid is effective.
179 */
Damien Miller4af51302000-04-16 11:18:38 +1000180void
Ben Lindstrom3fcf1a22001-04-08 18:26:59 +0000181permanently_set_uid(struct passwd *pw)
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000182{
Damien Miller4626cba2016-01-08 14:24:56 +1100183#ifndef NO_UID_RESTORATION_TEST
Damien Miller5fe46a42003-06-05 09:53:31 +1000184 uid_t old_uid = getuid();
185 gid_t old_gid = getgid();
Darren Tucker89c532d2014-01-18 20:43:49 +1100186#endif
Damien Miller5fe46a42003-06-05 09:53:31 +1000187
Damien Miller6b4069a2006-06-13 13:05:15 +1000188 if (pw == NULL)
189 fatal("permanently_set_uid: no user given");
Ben Lindstrom3fcf1a22001-04-08 18:26:59 +0000190 if (temporarily_use_uid_effective)
Ben Lindstromca8943e2002-06-06 20:42:04 +0000191 fatal("permanently_set_uid: temporarily_use_uid effective");
Ben Lindstrom1fa330c2002-07-23 21:29:49 +0000192 debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid,
193 (u_int)pw->pw_gid);
Damien Miller5fe46a42003-06-05 09:53:31 +1000194
deraadt@openbsd.org4d28fa72019-06-28 13:35:04 +0000195 if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) == -1)
Damien Miller5fe46a42003-06-05 09:53:31 +1000196 fatal("setresgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
Damien Miller5fe46a42003-06-05 09:53:31 +1000197
Damien Miller1598d6b2009-01-21 16:04:24 +1100198#ifdef __APPLE__
199 /*
200 * OS X requires initgroups after setgid to opt back into
201 * memberd support for >16 supplemental groups.
202 */
deraadt@openbsd.org4d28fa72019-06-28 13:35:04 +0000203 if (initgroups(pw->pw_name, pw->pw_gid) == -1)
Damien Miller1598d6b2009-01-21 16:04:24 +1100204 fatal("initgroups %.100s %u: %.100s",
205 pw->pw_name, (u_int)pw->pw_gid, strerror(errno));
206#endif
207
deraadt@openbsd.org4d28fa72019-06-28 13:35:04 +0000208 if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) == -1)
Damien Miller5fe46a42003-06-05 09:53:31 +1000209 fatal("setresuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
Damien Miller5fe46a42003-06-05 09:53:31 +1000210
Damien Miller4626cba2016-01-08 14:24:56 +1100211#ifndef NO_UID_RESTORATION_TEST
Damien Miller5fe46a42003-06-05 09:53:31 +1000212 /* Try restoration of GID if changed (test clearing of saved gid) */
Darren Tucker35beadd2004-10-19 16:33:33 +1000213 if (old_gid != pw->pw_gid && pw->pw_uid != 0 &&
Damien Miller5fe46a42003-06-05 09:53:31 +1000214 (setgid(old_gid) != -1 || setegid(old_gid) != -1))
Darren Tucker400b8782003-06-06 10:46:04 +1000215 fatal("%s: was able to restore old [e]gid", __func__);
Darren Tucker35beadd2004-10-19 16:33:33 +1000216#endif
Damien Miller5fe46a42003-06-05 09:53:31 +1000217
218 /* Verify GID drop was successful */
219 if (getgid() != pw->pw_gid || getegid() != pw->pw_gid) {
Damien Millera8e06ce2003-11-21 23:48:55 +1100220 fatal("%s: egid incorrect gid:%u egid:%u (should be %u)",
221 __func__, (u_int)getgid(), (u_int)getegid(),
Damien Miller5fe46a42003-06-05 09:53:31 +1000222 (u_int)pw->pw_gid);
223 }
224
Damien Miller4626cba2016-01-08 14:24:56 +1100225#ifndef NO_UID_RESTORATION_TEST
Damien Miller5fe46a42003-06-05 09:53:31 +1000226 /* Try restoration of UID if changed (test clearing of saved uid) */
Damien Millera8e06ce2003-11-21 23:48:55 +1100227 if (old_uid != pw->pw_uid &&
Damien Miller5fe46a42003-06-05 09:53:31 +1000228 (setuid(old_uid) != -1 || seteuid(old_uid) != -1))
Darren Tucker400b8782003-06-06 10:46:04 +1000229 fatal("%s: was able to restore old [e]uid", __func__);
Darren Tuckerfbe3b362003-09-22 12:54:37 +1000230#endif
Damien Miller5fe46a42003-06-05 09:53:31 +1000231
232 /* Verify UID drop was successful */
233 if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid) {
Damien Millera8e06ce2003-11-21 23:48:55 +1100234 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)",
235 __func__, (u_int)getuid(), (u_int)geteuid(),
Damien Miller5fe46a42003-06-05 09:53:31 +1000236 (u_int)pw->pw_uid);
237 }
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000238}