1 /* $OpenBSD: uidswap.c,v 1.29 2006/06/08 14:45:49 markus 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".
24 * Note: all these functions must work in all of the following cases:
28 * Additionally, they must work regardless of whether the system has
29 * POSIX saved uids or not.
32 #if defined(_POSIX_SAVED_IDS) && !defined(BROKEN_SAVED_UIDS)
33 /* Lets assume that posix saved ids also work with seteuid, even though that
34 is not part of the posix specification. */
35 #define SAVED_IDS_WORK_WITH_SETEUID
36 /* Saved effective uid. */
37 static uid_t saved_euid = 0;
38 static gid_t saved_egid = 0;
41 /* Saved effective uid. */
42 static int privileged = 0;
43 static int temporarily_use_uid_effective = 0;
44 static gid_t *saved_egroups = NULL, *user_groups = NULL;
45 static int saved_egroupslen = -1, user_groupslen = -1;
48 * Temporarily changes to the given uid. If the effective user
49 * id is not root, this does nothing. This call cannot be nested.
52 temporarily_use_uid(struct passwd *pw)
54 /* Save the current euid, and egroups. */
55 #ifdef SAVED_IDS_WORK_WITH_SETEUID
56 saved_euid = geteuid();
57 saved_egid = getegid();
58 debug("temporarily_use_uid: %u/%u (e=%u/%u)",
59 (u_int)pw->pw_uid, (u_int)pw->pw_gid,
60 (u_int)saved_euid, (u_int)saved_egid);
62 if (saved_euid != 0) {
72 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
75 temporarily_use_uid_effective = 1;
77 saved_egroupslen = getgroups(0, NULL);
78 if (saved_egroupslen < 0)
79 fatal("getgroups: %.100s", strerror(errno));
80 if (saved_egroupslen > 0) {
81 saved_egroups = xrealloc(saved_egroups,
82 saved_egroupslen, sizeof(gid_t));
83 if (getgroups(saved_egroupslen, saved_egroups) < 0)
84 fatal("getgroups: %.100s", strerror(errno));
85 } else { /* saved_egroupslen == 0 */
86 if (saved_egroups != NULL)
90 /* set and save the user's groups */
91 if (user_groupslen == -1) {
92 if (initgroups(pw->pw_name, pw->pw_gid) < 0)
93 fatal("initgroups: %s: %.100s", pw->pw_name,
96 user_groupslen = getgroups(0, NULL);
97 if (user_groupslen < 0)
98 fatal("getgroups: %.100s", strerror(errno));
99 if (user_groupslen > 0) {
100 user_groups = xrealloc(user_groups,
101 user_groupslen, sizeof(gid_t));
102 if (getgroups(user_groupslen, user_groups) < 0)
103 fatal("getgroups: %.100s", strerror(errno));
104 } else { /* user_groupslen == 0 */
109 /* Set the effective uid to the given (unprivileged) uid. */
110 if (setgroups(user_groupslen, user_groups) < 0)
111 fatal("setgroups: %.100s", strerror(errno));
112 #ifndef SAVED_IDS_WORK_WITH_SETEUID
113 /* Propagate the privileged gid to all of our gids. */
114 if (setgid(getegid()) < 0)
115 debug("setgid %u: %.100s", (u_int) getegid(), strerror(errno));
116 /* Propagate the privileged uid to all of our uids. */
117 if (setuid(geteuid()) < 0)
118 debug("setuid %u: %.100s", (u_int) geteuid(), strerror(errno));
119 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
120 if (setegid(pw->pw_gid) < 0)
121 fatal("setegid %u: %.100s", (u_int)pw->pw_gid,
123 if (seteuid(pw->pw_uid) == -1)
124 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid,
129 permanently_drop_suid(uid_t uid)
131 uid_t old_uid = getuid();
133 debug("permanently_drop_suid: %u", (u_int)uid);
134 #if defined(HAVE_SETRESUID) && !defined(BROKEN_SETRESUID)
135 if (setresuid(uid, uid, uid) < 0)
136 fatal("setresuid %u: %.100s", (u_int)uid, strerror(errno));
137 #elif defined(HAVE_SETREUID) && !defined(BROKEN_SETREUID)
138 if (setreuid(uid, uid) < 0)
139 fatal("setreuid %u: %.100s", (u_int)uid, strerror(errno));
141 # ifndef SETEUID_BREAKS_SETUID
142 if (seteuid(uid) < 0)
143 fatal("seteuid %u: %.100s", (u_int)uid, strerror(errno));
146 fatal("setuid %u: %.100s", (u_int)uid, strerror(errno));
150 /* Try restoration of UID if changed (test clearing of saved uid) */
151 if (old_uid != uid &&
152 (setuid(old_uid) != -1 || seteuid(old_uid) != -1))
153 fatal("%s: was able to restore old [e]uid", __func__);
156 /* Verify UID drop was successful */
157 if (getuid() != uid || geteuid() != uid) {
158 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)",
159 __func__, (u_int)getuid(), (u_int)geteuid(), (u_int)uid);
164 * Restores to the original (privileged) uid.
169 /* it's a no-op unless privileged */
171 debug("restore_uid: (unprivileged)");
174 if (!temporarily_use_uid_effective)
175 fatal("restore_uid: temporarily_use_uid not effective");
177 #ifdef SAVED_IDS_WORK_WITH_SETEUID
178 debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid);
179 /* Set the effective uid back to the saved privileged uid. */
180 if (seteuid(saved_euid) < 0)
181 fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno));
182 if (setegid(saved_egid) < 0)
183 fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno));
184 #else /* SAVED_IDS_WORK_WITH_SETEUID */
186 * We are unable to restore the real uid to its unprivileged value.
187 * Propagate the real uid (usually more privileged) to effective uid
192 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
194 if (setgroups(saved_egroupslen, saved_egroups) < 0)
195 fatal("setgroups: %.100s", strerror(errno));
196 temporarily_use_uid_effective = 0;
200 * Permanently sets all uids to the given uid. This cannot be
201 * called while temporarily_use_uid is effective.
204 permanently_set_uid(struct passwd *pw)
206 uid_t old_uid = getuid();
207 gid_t old_gid = getgid();
210 fatal("permanently_set_uid: no user given");
211 if (temporarily_use_uid_effective)
212 fatal("permanently_set_uid: temporarily_use_uid effective");
213 debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid,
216 #if defined(HAVE_SETRESGID) && !defined(BROKEN_SETRESGID)
217 if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) < 0)
218 fatal("setresgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
219 #elif defined(HAVE_SETREGID) && !defined(BROKEN_SETREGID)
220 if (setregid(pw->pw_gid, pw->pw_gid) < 0)
221 fatal("setregid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
223 if (setegid(pw->pw_gid) < 0)
224 fatal("setegid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
225 if (setgid(pw->pw_gid) < 0)
226 fatal("setgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
229 #if defined(HAVE_SETRESUID) && !defined(BROKEN_SETRESUID)
230 if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) < 0)
231 fatal("setresuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
232 #elif defined(HAVE_SETREUID) && !defined(BROKEN_SETREUID)
233 if (setreuid(pw->pw_uid, pw->pw_uid) < 0)
234 fatal("setreuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
236 # ifndef SETEUID_BREAKS_SETUID
237 if (seteuid(pw->pw_uid) < 0)
238 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
240 if (setuid(pw->pw_uid) < 0)
241 fatal("setuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
245 /* Try restoration of GID if changed (test clearing of saved gid) */
246 if (old_gid != pw->pw_gid && pw->pw_uid != 0 &&
247 (setgid(old_gid) != -1 || setegid(old_gid) != -1))
248 fatal("%s: was able to restore old [e]gid", __func__);
251 /* Verify GID drop was successful */
252 if (getgid() != pw->pw_gid || getegid() != pw->pw_gid) {
253 fatal("%s: egid incorrect gid:%u egid:%u (should be %u)",
254 __func__, (u_int)getgid(), (u_int)getegid(),
259 /* Try restoration of UID if changed (test clearing of saved uid) */
260 if (old_uid != pw->pw_uid &&
261 (setuid(old_uid) != -1 || seteuid(old_uid) != -1))
262 fatal("%s: was able to restore old [e]uid", __func__);
265 /* Verify UID drop was successful */
266 if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid) {
267 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)",
268 __func__, (u_int)getuid(), (u_int)geteuid(),