1 /* $OpenBSD: uidswap.c,v 1.31 2006/07/11 20:07:25 stevesk 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/types.h>
29 * Note: all these functions must work in all of the following cases:
33 * Additionally, they must work regardless of whether the system has
34 * POSIX saved uids or not.
37 #if defined(_POSIX_SAVED_IDS) && !defined(BROKEN_SAVED_UIDS)
38 /* Lets assume that posix saved ids also work with seteuid, even though that
39 is not part of the posix specification. */
40 #define SAVED_IDS_WORK_WITH_SETEUID
41 /* Saved effective uid. */
42 static uid_t saved_euid = 0;
43 static gid_t saved_egid = 0;
46 /* Saved effective uid. */
47 static int privileged = 0;
48 static int temporarily_use_uid_effective = 0;
49 static gid_t *saved_egroups = NULL, *user_groups = NULL;
50 static int saved_egroupslen = -1, user_groupslen = -1;
53 * Temporarily changes to the given uid. If the effective user
54 * id is not root, this does nothing. This call cannot be nested.
57 temporarily_use_uid(struct passwd *pw)
59 /* Save the current euid, and egroups. */
60 #ifdef SAVED_IDS_WORK_WITH_SETEUID
61 saved_euid = geteuid();
62 saved_egid = getegid();
63 debug("temporarily_use_uid: %u/%u (e=%u/%u)",
64 (u_int)pw->pw_uid, (u_int)pw->pw_gid,
65 (u_int)saved_euid, (u_int)saved_egid);
67 if (saved_euid != 0) {
77 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
80 temporarily_use_uid_effective = 1;
82 saved_egroupslen = getgroups(0, NULL);
83 if (saved_egroupslen < 0)
84 fatal("getgroups: %.100s", strerror(errno));
85 if (saved_egroupslen > 0) {
86 saved_egroups = xrealloc(saved_egroups,
87 saved_egroupslen, sizeof(gid_t));
88 if (getgroups(saved_egroupslen, saved_egroups) < 0)
89 fatal("getgroups: %.100s", strerror(errno));
90 } else { /* saved_egroupslen == 0 */
91 if (saved_egroups != NULL)
95 /* set and save the user's groups */
96 if (user_groupslen == -1) {
97 if (initgroups(pw->pw_name, pw->pw_gid) < 0)
98 fatal("initgroups: %s: %.100s", pw->pw_name,
101 user_groupslen = getgroups(0, NULL);
102 if (user_groupslen < 0)
103 fatal("getgroups: %.100s", strerror(errno));
104 if (user_groupslen > 0) {
105 user_groups = xrealloc(user_groups,
106 user_groupslen, sizeof(gid_t));
107 if (getgroups(user_groupslen, user_groups) < 0)
108 fatal("getgroups: %.100s", strerror(errno));
109 } 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 defined(HAVE_SETRESUID) && !defined(BROKEN_SETRESUID)
140 if (setresuid(uid, uid, uid) < 0)
141 fatal("setresuid %u: %.100s", (u_int)uid, strerror(errno));
142 #elif defined(HAVE_SETREUID) && !defined(BROKEN_SETREUID)
143 if (setreuid(uid, uid) < 0)
144 fatal("setreuid %u: %.100s", (u_int)uid, strerror(errno));
146 # ifndef SETEUID_BREAKS_SETUID
147 if (seteuid(uid) < 0)
148 fatal("seteuid %u: %.100s", (u_int)uid, strerror(errno));
151 fatal("setuid %u: %.100s", (u_int)uid, strerror(errno));
155 /* Try restoration of UID if changed (test clearing of saved uid) */
156 if (old_uid != uid &&
157 (setuid(old_uid) != -1 || seteuid(old_uid) != -1))
158 fatal("%s: was able to restore old [e]uid", __func__);
161 /* Verify UID drop was successful */
162 if (getuid() != uid || geteuid() != uid) {
163 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)",
164 __func__, (u_int)getuid(), (u_int)geteuid(), (u_int)uid);
169 * Restores to the original (privileged) uid.
174 /* it's a no-op unless privileged */
176 debug("restore_uid: (unprivileged)");
179 if (!temporarily_use_uid_effective)
180 fatal("restore_uid: temporarily_use_uid not effective");
182 #ifdef SAVED_IDS_WORK_WITH_SETEUID
183 debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid);
184 /* Set the effective uid back to the saved privileged uid. */
185 if (seteuid(saved_euid) < 0)
186 fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno));
187 if (setegid(saved_egid) < 0)
188 fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno));
189 #else /* SAVED_IDS_WORK_WITH_SETEUID */
191 * We are unable to restore the real uid to its unprivileged value.
192 * Propagate the real uid (usually more privileged) to effective uid
197 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
199 if (setgroups(saved_egroupslen, saved_egroups) < 0)
200 fatal("setgroups: %.100s", strerror(errno));
201 temporarily_use_uid_effective = 0;
205 * Permanently sets all uids to the given uid. This cannot be
206 * called while temporarily_use_uid is effective.
209 permanently_set_uid(struct passwd *pw)
211 uid_t old_uid = getuid();
212 gid_t old_gid = getgid();
215 fatal("permanently_set_uid: no user given");
216 if (temporarily_use_uid_effective)
217 fatal("permanently_set_uid: temporarily_use_uid effective");
218 debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid,
221 #if defined(HAVE_SETRESGID) && !defined(BROKEN_SETRESGID)
222 if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) < 0)
223 fatal("setresgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
224 #elif defined(HAVE_SETREGID) && !defined(BROKEN_SETREGID)
225 if (setregid(pw->pw_gid, pw->pw_gid) < 0)
226 fatal("setregid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
228 if (setegid(pw->pw_gid) < 0)
229 fatal("setegid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
230 if (setgid(pw->pw_gid) < 0)
231 fatal("setgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
234 #if defined(HAVE_SETRESUID) && !defined(BROKEN_SETRESUID)
235 if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) < 0)
236 fatal("setresuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
237 #elif defined(HAVE_SETREUID) && !defined(BROKEN_SETREUID)
238 if (setreuid(pw->pw_uid, pw->pw_uid) < 0)
239 fatal("setreuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
241 # ifndef SETEUID_BREAKS_SETUID
242 if (seteuid(pw->pw_uid) < 0)
243 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
245 if (setuid(pw->pw_uid) < 0)
246 fatal("setuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
250 /* Try restoration of GID if changed (test clearing of saved gid) */
251 if (old_gid != pw->pw_gid && pw->pw_uid != 0 &&
252 (setgid(old_gid) != -1 || setegid(old_gid) != -1))
253 fatal("%s: was able to restore old [e]gid", __func__);
256 /* Verify GID drop was successful */
257 if (getgid() != pw->pw_gid || getegid() != pw->pw_gid) {
258 fatal("%s: egid incorrect gid:%u egid:%u (should be %u)",
259 __func__, (u_int)getgid(), (u_int)getegid(),
264 /* Try restoration of UID if changed (test clearing of saved uid) */
265 if (old_uid != pw->pw_uid &&
266 (setuid(old_uid) != -1 || seteuid(old_uid) != -1))
267 fatal("%s: was able to restore old [e]uid", __func__);
270 /* Verify UID drop was successful */
271 if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid) {
272 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)",
273 __func__, (u_int)getuid(), (u_int)geteuid(),