1 /* $OpenBSD: uidswap.c,v 1.34 2006/07/26 02:35:17 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>
18 #include <sys/param.h>
32 * Note: all these functions must work in all of the following cases:
36 * Additionally, they must work regardless of whether the system has
37 * POSIX saved uids or not.
40 #if defined(_POSIX_SAVED_IDS) && !defined(BROKEN_SAVED_UIDS)
41 /* Lets assume that posix saved ids also work with seteuid, even though that
42 is not part of the posix specification. */
43 #define SAVED_IDS_WORK_WITH_SETEUID
44 /* Saved effective uid. */
45 static uid_t saved_euid = 0;
46 static gid_t saved_egid = 0;
49 /* Saved effective uid. */
50 static int privileged = 0;
51 static int temporarily_use_uid_effective = 0;
52 static gid_t *saved_egroups = NULL, *user_groups = NULL;
53 static int saved_egroupslen = -1, user_groupslen = -1;
56 * Temporarily changes to the given uid. If the effective user
57 * id is not root, this does nothing. This call cannot be nested.
60 temporarily_use_uid(struct passwd *pw)
62 /* Save the current euid, and egroups. */
63 #ifdef SAVED_IDS_WORK_WITH_SETEUID
64 saved_euid = geteuid();
65 saved_egid = getegid();
66 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);
70 if (saved_euid != 0) {
80 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
83 temporarily_use_uid_effective = 1;
85 saved_egroupslen = getgroups(0, NULL);
86 if (saved_egroupslen < 0)
87 fatal("getgroups: %.100s", strerror(errno));
88 if (saved_egroupslen > 0) {
89 saved_egroups = xrealloc(saved_egroups,
90 saved_egroupslen, sizeof(gid_t));
91 if (getgroups(saved_egroupslen, saved_egroups) < 0)
92 fatal("getgroups: %.100s", strerror(errno));
93 } else { /* saved_egroupslen == 0 */
94 if (saved_egroups != NULL)
98 /* set and save the user's groups */
99 if (user_groupslen == -1) {
100 if (initgroups(pw->pw_name, pw->pw_gid) < 0)
101 fatal("initgroups: %s: %.100s", pw->pw_name,
104 user_groupslen = getgroups(0, NULL);
105 if (user_groupslen < 0)
106 fatal("getgroups: %.100s", strerror(errno));
107 if (user_groupslen > 0) {
108 user_groups = xrealloc(user_groups,
109 user_groupslen, sizeof(gid_t));
110 if (getgroups(user_groupslen, user_groups) < 0)
111 fatal("getgroups: %.100s", strerror(errno));
112 } else { /* user_groupslen == 0 */
117 /* Set the effective uid to the given (unprivileged) uid. */
118 if (setgroups(user_groupslen, user_groups) < 0)
119 fatal("setgroups: %.100s", strerror(errno));
120 #ifndef SAVED_IDS_WORK_WITH_SETEUID
121 /* Propagate the privileged gid to all of our gids. */
122 if (setgid(getegid()) < 0)
123 debug("setgid %u: %.100s", (u_int) getegid(), strerror(errno));
124 /* Propagate the privileged uid to all of our uids. */
125 if (setuid(geteuid()) < 0)
126 debug("setuid %u: %.100s", (u_int) geteuid(), strerror(errno));
127 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
128 if (setegid(pw->pw_gid) < 0)
129 fatal("setegid %u: %.100s", (u_int)pw->pw_gid,
131 if (seteuid(pw->pw_uid) == -1)
132 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid,
137 permanently_drop_suid(uid_t uid)
139 uid_t old_uid = getuid();
141 debug("permanently_drop_suid: %u", (u_int)uid);
142 #if defined(HAVE_SETRESUID) && !defined(BROKEN_SETRESUID)
143 if (setresuid(uid, uid, uid) < 0)
144 fatal("setresuid %u: %.100s", (u_int)uid, strerror(errno));
145 #elif defined(HAVE_SETREUID) && !defined(BROKEN_SETREUID)
146 if (setreuid(uid, uid) < 0)
147 fatal("setreuid %u: %.100s", (u_int)uid, strerror(errno));
149 # ifndef SETEUID_BREAKS_SETUID
150 if (seteuid(uid) < 0)
151 fatal("seteuid %u: %.100s", (u_int)uid, strerror(errno));
154 fatal("setuid %u: %.100s", (u_int)uid, strerror(errno));
158 /* Try restoration of UID if changed (test clearing of saved uid) */
159 if (old_uid != uid &&
160 (setuid(old_uid) != -1 || seteuid(old_uid) != -1))
161 fatal("%s: was able to restore old [e]uid", __func__);
164 /* Verify UID drop was successful */
165 if (getuid() != uid || geteuid() != uid) {
166 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)",
167 __func__, (u_int)getuid(), (u_int)geteuid(), (u_int)uid);
172 * Restores to the original (privileged) uid.
177 /* it's a no-op unless privileged */
179 debug("restore_uid: (unprivileged)");
182 if (!temporarily_use_uid_effective)
183 fatal("restore_uid: temporarily_use_uid not effective");
185 #ifdef SAVED_IDS_WORK_WITH_SETEUID
186 debug("restore_uid: %u/%u", (u_int)saved_euid, (u_int)saved_egid);
187 /* Set the effective uid back to the saved privileged uid. */
188 if (seteuid(saved_euid) < 0)
189 fatal("seteuid %u: %.100s", (u_int)saved_euid, strerror(errno));
190 if (setegid(saved_egid) < 0)
191 fatal("setegid %u: %.100s", (u_int)saved_egid, strerror(errno));
192 #else /* SAVED_IDS_WORK_WITH_SETEUID */
194 * We are unable to restore the real uid to its unprivileged value.
195 * Propagate the real uid (usually more privileged) to effective uid
200 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
202 if (setgroups(saved_egroupslen, saved_egroups) < 0)
203 fatal("setgroups: %.100s", strerror(errno));
204 temporarily_use_uid_effective = 0;
208 * Permanently sets all uids to the given uid. This cannot be
209 * called while temporarily_use_uid is effective.
212 permanently_set_uid(struct passwd *pw)
214 uid_t old_uid = getuid();
215 gid_t old_gid = getgid();
218 fatal("permanently_set_uid: no user given");
219 if (temporarily_use_uid_effective)
220 fatal("permanently_set_uid: temporarily_use_uid effective");
221 debug("permanently_set_uid: %u/%u", (u_int)pw->pw_uid,
224 #if defined(HAVE_SETRESGID) && !defined(BROKEN_SETRESGID)
225 if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) < 0)
226 fatal("setresgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
227 #elif defined(HAVE_SETREGID) && !defined(BROKEN_SETREGID)
228 if (setregid(pw->pw_gid, pw->pw_gid) < 0)
229 fatal("setregid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
231 if (setegid(pw->pw_gid) < 0)
232 fatal("setegid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
233 if (setgid(pw->pw_gid) < 0)
234 fatal("setgid %u: %.100s", (u_int)pw->pw_gid, strerror(errno));
237 #if defined(HAVE_SETRESUID) && !defined(BROKEN_SETRESUID)
238 if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) < 0)
239 fatal("setresuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
240 #elif defined(HAVE_SETREUID) && !defined(BROKEN_SETREUID)
241 if (setreuid(pw->pw_uid, pw->pw_uid) < 0)
242 fatal("setreuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
244 # ifndef SETEUID_BREAKS_SETUID
245 if (seteuid(pw->pw_uid) < 0)
246 fatal("seteuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
248 if (setuid(pw->pw_uid) < 0)
249 fatal("setuid %u: %.100s", (u_int)pw->pw_uid, strerror(errno));
253 /* Try restoration of GID if changed (test clearing of saved gid) */
254 if (old_gid != pw->pw_gid && pw->pw_uid != 0 &&
255 (setgid(old_gid) != -1 || setegid(old_gid) != -1))
256 fatal("%s: was able to restore old [e]gid", __func__);
259 /* Verify GID drop was successful */
260 if (getgid() != pw->pw_gid || getegid() != pw->pw_gid) {
261 fatal("%s: egid incorrect gid:%u egid:%u (should be %u)",
262 __func__, (u_int)getgid(), (u_int)getegid(),
267 /* Try restoration of UID if changed (test clearing of saved uid) */
268 if (old_uid != pw->pw_uid &&
269 (setuid(old_uid) != -1 || seteuid(old_uid) != -1))
270 fatal("%s: was able to restore old [e]uid", __func__);
273 /* Verify UID drop was successful */
274 if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid) {
275 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)",
276 __func__, (u_int)getuid(), (u_int)geteuid(),