1 /* $OpenBSD: uidswap.c,v 1.35 2006/08/03 03:34:42 deraadt Exp $ */
3 * Author: Tatu Ylonen <ylo@cs.hut.fi>
4 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
6 * Code for uid-swapping.
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".
17 #include <sys/param.h>
31 * Note: all these functions must work in all of the following cases:
35 * Additionally, they must work regardless of whether the system has
36 * POSIX saved uids or not.
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. */
44 static uid_t saved_euid = 0;
45 static gid_t saved_egid = 0;
48 /* Saved effective uid. */
49 static int privileged = 0;
50 static int temporarily_use_uid_effective = 0;
51 static gid_t *saved_egroups = NULL, *user_groups = NULL;
52 static int saved_egroupslen = -1, user_groupslen = -1;
55 * Temporarily changes to the given uid. If the effective user
56 * id is not root, this does nothing. This call cannot be nested.
59 temporarily_use_uid(struct passwd *pw)
61 /* Save the current euid, and egroups. */
62 #ifdef SAVED_IDS_WORK_WITH_SETEUID
63 saved_euid = geteuid();
64 saved_egid = getegid();
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);
69 if (saved_euid != 0) {
79 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
82 temporarily_use_uid_effective = 1;
84 saved_egroupslen = getgroups(0, NULL);
85 if (saved_egroupslen < 0)
86 fatal("getgroups: %.100s", strerror(errno));
87 if (saved_egroupslen > 0) {
88 saved_egroups = xrealloc(saved_egroups,
89 saved_egroupslen, sizeof(gid_t));
90 if (getgroups(saved_egroupslen, saved_egroups) < 0)
91 fatal("getgroups: %.100s", strerror(errno));
92 } else { /* saved_egroupslen == 0 */
96 /* set and save the user's groups */
97 if (user_groupslen == -1) {
98 if (initgroups(pw->pw_name, pw->pw_gid) < 0)
99 fatal("initgroups: %s: %.100s", pw->pw_name,
102 user_groupslen = getgroups(0, NULL);
103 if (user_groupslen < 0)
104 fatal("getgroups: %.100s", strerror(errno));
105 if (user_groupslen > 0) {
106 user_groups = xrealloc(user_groups,
107 user_groupslen, sizeof(gid_t));
108 if (getgroups(user_groupslen, user_groups) < 0)
109 fatal("getgroups: %.100s", strerror(errno));
110 } else { /* user_groupslen == 0 */
114 /* Set the effective uid to the given (unprivileged) uid. */
115 if (setgroups(user_groupslen, user_groups) < 0)
116 fatal("setgroups: %.100s", strerror(errno));
117 #ifndef SAVED_IDS_WORK_WITH_SETEUID
118 /* Propagate the privileged gid to all of our gids. */
119 if (setgid(getegid()) < 0)
120 debug("setgid %u: %.100s", (u_int) getegid(), strerror(errno));
121 /* Propagate the privileged uid to all of our uids. */
122 if (setuid(geteuid()) < 0)
123 debug("setuid %u: %.100s", (u_int) geteuid(), strerror(errno));
124 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
125 if (setegid(pw->pw_gid) < 0)
126 fatal("setegid %u: %.100s", (u_int)pw->pw_gid,
128 if (seteuid(pw->pw_uid) == -1)
129 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid,
134 permanently_drop_suid(uid_t uid)
136 uid_t old_uid = getuid();
138 debug("permanently_drop_suid: %u", (u_int)uid);
139 if (setresuid(uid, uid, uid) < 0)
140 fatal("setresuid %u: %.100s", (u_int)uid, strerror(errno));
143 /* Try restoration of UID if changed (test clearing of saved uid) */
144 if (old_uid != uid &&
145 (setuid(old_uid) != -1 || seteuid(old_uid) != -1))
146 fatal("%s: was able to restore old [e]uid", __func__);
149 /* Verify UID drop was successful */
150 if (getuid() != uid || geteuid() != uid) {
151 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)",
152 __func__, (u_int)getuid(), (u_int)geteuid(), (u_int)uid);
157 * Restores to the original (privileged) uid.
162 /* it's a no-op unless privileged */
164 debug("restore_uid: (unprivileged)");
167 if (!temporarily_use_uid_effective)
168 fatal("restore_uid: temporarily_use_uid not effective");
170 #ifdef SAVED_IDS_WORK_WITH_SETEUID
171 debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid);
172 /* Set the effective uid back to the saved privileged uid. */
173 if (seteuid(saved_euid) < 0)
174 fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno));
175 if (setegid(saved_egid) < 0)
176 fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno));
177 #else /* SAVED_IDS_WORK_WITH_SETEUID */
179 * We are unable to restore the real uid to its unprivileged value.
180 * Propagate the real uid (usually more privileged) to effective uid
185 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
187 if (setgroups(saved_egroupslen, saved_egroups) < 0)
188 fatal("setgroups: %.100s", strerror(errno));
189 temporarily_use_uid_effective = 0;
193 * Permanently sets all uids to the given uid. This cannot be
194 * called while temporarily_use_uid is effective.
197 permanently_set_uid(struct passwd *pw)
199 uid_t old_uid = getuid();
200 gid_t old_gid = getgid();
203 fatal("permanently_set_uid: no user given");
204 if (temporarily_use_uid_effective)
205 fatal("permanently_set_uid: temporarily_use_uid effective");
206 debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid,
209 if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) < 0)
210 fatal("setresgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
214 * OS X requires initgroups after setgid to opt back into
215 * memberd support for >16 supplemental groups.
217 if (initgroups(pw->pw_name, pw->pw_gid) < 0)
218 fatal("initgroups %.100s %u: %.100s",
219 pw->pw_name, (u_int)pw->pw_gid, strerror(errno));
222 if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) < 0)
223 fatal("setresuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
226 /* Try restoration of GID if changed (test clearing of saved gid) */
227 if (old_gid != pw->pw_gid && pw->pw_uid != 0 &&
228 (setgid(old_gid) != -1 || setegid(old_gid) != -1))
229 fatal("%s: was able to restore old [e]gid", __func__);
232 /* Verify GID drop was successful */
233 if (getgid() != pw->pw_gid || getegid() != pw->pw_gid) {
234 fatal("%s: egid incorrect gid:%u egid:%u (should be %u)",
235 __func__, (u_int)getgid(), (u_int)getegid(),
240 /* Try restoration of UID if changed (test clearing of saved uid) */
241 if (old_uid != pw->pw_uid &&
242 (setuid(old_uid) != -1 || seteuid(old_uid) != -1))
243 fatal("%s: was able to restore old [e]uid", __func__);
246 /* Verify UID drop was successful */
247 if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid) {
248 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)",
249 __func__, (u_int)getuid(), (u_int)geteuid(),