1 /* $OpenBSD: uidswap.c,v 1.36 2013/11/08 11:15:19 dtucker 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>
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 */
97 /* set and save the user's groups */
98 if (user_groupslen
== -1) {
99 if (initgroups(pw
->pw_name
, pw
->pw_gid
) < 0)
100 fatal("initgroups: %s: %.100s", pw
->pw_name
,
103 user_groupslen
= getgroups(0, NULL
);
104 if (user_groupslen
< 0)
105 fatal("getgroups: %.100s", strerror(errno
));
106 if (user_groupslen
> 0) {
107 user_groups
= xrealloc(user_groups
,
108 user_groupslen
, sizeof(gid_t
));
109 if (getgroups(user_groupslen
, user_groups
) < 0)
110 fatal("getgroups: %.100s", strerror(errno
));
111 } else { /* user_groupslen == 0 */
115 /* Set the effective uid to the given (unprivileged) uid. */
116 if (setgroups(user_groupslen
, user_groups
) < 0)
117 fatal("setgroups: %.100s", strerror(errno
));
118 #ifndef SAVED_IDS_WORK_WITH_SETEUID
119 /* Propagate the privileged gid to all of our gids. */
120 if (setgid(getegid()) < 0)
121 debug("setgid %u: %.100s", (u_int
) getegid(), strerror(errno
));
122 /* Propagate the privileged uid to all of our uids. */
123 if (setuid(geteuid()) < 0)
124 debug("setuid %u: %.100s", (u_int
) geteuid(), strerror(errno
));
125 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
126 if (setegid(pw
->pw_gid
) < 0)
127 fatal("setegid %u: %.100s", (u_int
)pw
->pw_gid
,
129 if (seteuid(pw
->pw_uid
) == -1)
130 fatal("seteuid %u: %.100s", (u_int
)pw
->pw_uid
,
135 permanently_drop_suid(uid_t uid
)
138 uid_t old_uid
= getuid();
141 debug("permanently_drop_suid: %u", (u_int
)uid
);
142 if (setresuid(uid
, uid
, uid
) < 0)
143 fatal("setresuid %u: %.100s", (u_int
)uid
, strerror(errno
));
146 /* Try restoration of UID if changed (test clearing of saved uid) */
147 if (old_uid
!= uid
&&
148 (setuid(old_uid
) != -1 || seteuid(old_uid
) != -1))
149 fatal("%s: was able to restore old [e]uid", __func__
);
152 /* Verify UID drop was successful */
153 if (getuid() != uid
|| geteuid() != uid
) {
154 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)",
155 __func__
, (u_int
)getuid(), (u_int
)geteuid(), (u_int
)uid
);
160 * Restores to the original (privileged) uid.
165 /* it's a no-op unless privileged */
167 debug("restore_uid: (unprivileged)");
170 if (!temporarily_use_uid_effective
)
171 fatal("restore_uid: temporarily_use_uid not effective");
173 #ifdef SAVED_IDS_WORK_WITH_SETEUID
174 debug("restore_uid: %u/%u", (u_int
)saved_euid
, (u_int
)saved_egid
);
175 /* Set the effective uid back to the saved privileged uid. */
176 if (seteuid(saved_euid
) < 0)
177 fatal("seteuid %u: %.100s", (u_int
)saved_euid
, strerror(errno
));
178 if (setegid(saved_egid
) < 0)
179 fatal("setegid %u: %.100s", (u_int
)saved_egid
, strerror(errno
));
180 #else /* SAVED_IDS_WORK_WITH_SETEUID */
182 * We are unable to restore the real uid to its unprivileged value.
183 * Propagate the real uid (usually more privileged) to effective uid
188 #endif /* SAVED_IDS_WORK_WITH_SETEUID */
190 if (setgroups(saved_egroupslen
, saved_egroups
) < 0)
191 fatal("setgroups: %.100s", strerror(errno
));
192 temporarily_use_uid_effective
= 0;
196 * Permanently sets all uids to the given uid. This cannot be
197 * called while temporarily_use_uid is effective.
200 permanently_set_uid(struct passwd
*pw
)
203 uid_t old_uid
= getuid();
204 gid_t old_gid
= getgid();
208 fatal("permanently_set_uid: no user given");
209 if (temporarily_use_uid_effective
)
210 fatal("permanently_set_uid: temporarily_use_uid effective");
211 debug("permanently_set_uid: %u/%u", (u_int
)pw
->pw_uid
,
214 if (setresgid(pw
->pw_gid
, pw
->pw_gid
, pw
->pw_gid
) < 0)
215 fatal("setresgid %u: %.100s", (u_int
)pw
->pw_gid
, strerror(errno
));
219 * OS X requires initgroups after setgid to opt back into
220 * memberd support for >16 supplemental groups.
222 if (initgroups(pw
->pw_name
, pw
->pw_gid
) < 0)
223 fatal("initgroups %.100s %u: %.100s",
224 pw
->pw_name
, (u_int
)pw
->pw_gid
, strerror(errno
));
227 if (setresuid(pw
->pw_uid
, pw
->pw_uid
, pw
->pw_uid
) < 0)
228 fatal("setresuid %u: %.100s", (u_int
)pw
->pw_uid
, strerror(errno
));
231 /* Try restoration of GID if changed (test clearing of saved gid) */
232 if (old_gid
!= pw
->pw_gid
&& pw
->pw_uid
!= 0 &&
233 (setgid(old_gid
) != -1 || setegid(old_gid
) != -1))
234 fatal("%s: was able to restore old [e]gid", __func__
);
237 /* Verify GID drop was successful */
238 if (getgid() != pw
->pw_gid
|| getegid() != pw
->pw_gid
) {
239 fatal("%s: egid incorrect gid:%u egid:%u (should be %u)",
240 __func__
, (u_int
)getgid(), (u_int
)getegid(),
245 /* Try restoration of UID if changed (test clearing of saved uid) */
246 if (old_uid
!= pw
->pw_uid
&&
247 (setuid(old_uid
) != -1 || seteuid(old_uid
) != -1))
248 fatal("%s: was able to restore old [e]uid", __func__
);
251 /* Verify UID drop was successful */
252 if (getuid() != pw
->pw_uid
|| geteuid() != pw
->pw_uid
) {
253 fatal("%s: euid incorrect uid:%u euid:%u (should be %u)",
254 __func__
, (u_int
)getuid(), (u_int
)geteuid(),