1 /*-
2 * SPDX-License-Identifier: BSD-2-Clause
3 *
4 * Copyright (c) 2006 nCircle Network Security, Inc.
5 * Copyright (c) 2009 Robert N. M. Watson
6 * Copyright (c) 2020 Mariusz Zaborski <oshogbo@FreeBSD.org>
7 * All rights reserved.
8 *
9 * This software was developed by Robert N. M. Watson for the TrustedBSD
10 * Project under contract to nCircle Network Security, Inc.
11 *
12 * Redistribution and use in source and binary forms, with or without
13 * modification, are permitted provided that the following conditions
14 * are met:
15 * 1. Redistributions of source code must retain the above copyright
16 * notice, this list of conditions and the following disclaimer.
17 * 2. Redistributions in binary form must reproduce the above copyright
18 * notice, this list of conditions and the following disclaimer in the
19 * documentation and/or other materials provided with the distribution.
20 *
21 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR, NCIRCLE NETWORK SECURITY,
25 * INC., OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
26 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
27 * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
28 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
29 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
30 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
31 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
32 */
33
34 #include <sys/cdefs.h>
35 #include <sys/param.h>
36 #include <sys/jail.h>
37 #include <sys/kernel.h>
38 #include <sys/lock.h>
39 #include <sys/mutex.h>
40 #include <sys/sx.h>
41 #include <sys/priv.h>
42 #include <sys/proc.h>
43 #include <sys/sdt.h>
44 #include <sys/sysctl.h>
45 #include <sys/systm.h>
46
47 #include <security/mac/mac_framework.h>
48
49 /*
50 * `suser_enabled' (which can be set by the security.bsd.suser_enabled
51 * sysctl) determines whether the system 'super-user' policy is in effect. If
52 * it is nonzero, an effective uid of 0 connotes special privilege,
53 * overriding many mandatory and discretionary protections. If it is zero,
54 * uid 0 is offered no special privilege in the kernel security policy.
55 * Setting it to zero may seriously impact the functionality of many existing
56 * userland programs, and should not be done without careful consideration of
57 * the consequences.
58 */
59
60 static bool
suser_enabled(struct ucred * cred)61 suser_enabled(struct ucred *cred)
62 {
63
64 return (prison_allow(cred, PR_ALLOW_SUSER));
65 }
66
67 static int
sysctl_kern_suser_enabled(SYSCTL_HANDLER_ARGS)68 sysctl_kern_suser_enabled(SYSCTL_HANDLER_ARGS)
69 {
70 struct ucred *cred;
71 int error, enabled;
72
73 cred = req->td->td_ucred;
74 enabled = suser_enabled(cred);
75 error = sysctl_handle_int(oidp, &enabled, 0, req);
76 if (error || !req->newptr)
77 return (error);
78 prison_set_allow(cred, PR_ALLOW_SUSER, enabled);
79 return (0);
80 }
81
82 SYSCTL_PROC(_security_bsd, OID_AUTO, suser_enabled, CTLTYPE_INT |
83 CTLFLAG_RWTUN | CTLFLAG_PRISON | CTLFLAG_MPSAFE, 0, 0,
84 &sysctl_kern_suser_enabled, "I", "Processes with uid 0 have privilege");
85
86 static int unprivileged_mlock = 1;
87 SYSCTL_INT(_security_bsd, OID_AUTO, unprivileged_mlock, CTLFLAG_RWTUN,
88 &unprivileged_mlock, 0, "Allow non-root users to call mlock(2)");
89
90 static int unprivileged_read_msgbuf = 1;
91 SYSCTL_INT(_security_bsd, OID_AUTO, unprivileged_read_msgbuf,
92 CTLFLAG_RW, &unprivileged_read_msgbuf, 0,
93 "Unprivileged processes may read the kernel message buffer");
94
95 SDT_PROVIDER_DEFINE(priv);
96 SDT_PROBE_DEFINE1(priv, kernel, priv_check, priv__ok, "int");
97 SDT_PROBE_DEFINE1(priv, kernel, priv_check, priv__err, "int");
98
99 static __always_inline int
priv_check_cred_pre(struct ucred * cred,int priv)100 priv_check_cred_pre(struct ucred *cred, int priv)
101 {
102 int error;
103
104 #ifdef MAC
105 error = mac_priv_check(cred, priv);
106 #else
107 error = 0;
108 #endif
109 return (error);
110 }
111
112 static __always_inline int
priv_check_cred_post(struct ucred * cred,int priv,int error,bool handled)113 priv_check_cred_post(struct ucred *cred, int priv, int error, bool handled)
114 {
115
116 if (__predict_true(handled))
117 goto out;
118 /*
119 * Now check with MAC, if enabled, to see if a policy module grants
120 * privilege.
121 */
122 #ifdef MAC
123 if (mac_priv_grant(cred, priv) == 0) {
124 error = 0;
125 goto out;
126 }
127 #endif
128
129 /*
130 * The default is deny, so if no policies have granted it, reject
131 * with a privilege error here.
132 */
133 error = EPERM;
134 out:
135 if (SDT_PROBES_ENABLED()) {
136 if (error)
137 SDT_PROBE1(priv, kernel, priv_check, priv__err, priv);
138 else
139 SDT_PROBE1(priv, kernel, priv_check, priv__ok, priv);
140 }
141 return (error);
142 }
143
144 /*
145 * Check a credential for privilege. Lots of good reasons to deny privilege;
146 * only a few to grant it.
147 */
148 int
priv_check_cred(struct ucred * cred,int priv)149 priv_check_cred(struct ucred *cred, int priv)
150 {
151 int error;
152
153 KASSERT(PRIV_VALID(priv), ("priv_check_cred: invalid privilege %d",
154 priv));
155
156 switch (priv) {
157 case PRIV_VFS_LOOKUP:
158 return (priv_check_cred_vfs_lookup(cred));
159 case PRIV_VFS_GENERATION:
160 return (priv_check_cred_vfs_generation(cred));
161 }
162
163 /*
164 * We first evaluate policies that may deny the granting of
165 * privilege unilaterally.
166 */
167 error = priv_check_cred_pre(cred, priv);
168 if (error)
169 goto out;
170
171 /*
172 * Jail policy will restrict certain privileges that may otherwise be
173 * be granted.
174 */
175 error = prison_priv_check(cred, priv);
176 if (error)
177 goto out;
178
179 if (unprivileged_mlock) {
180 /*
181 * Allow unprivileged users to call mlock(2)/munlock(2) and
182 * mlockall(2)/munlockall(2).
183 */
184 switch (priv) {
185 case PRIV_VM_MLOCK:
186 case PRIV_VM_MUNLOCK:
187 error = 0;
188 goto out;
189 }
190 }
191
192 if (unprivileged_read_msgbuf) {
193 /*
194 * Allow an unprivileged user to read the kernel message
195 * buffer.
196 */
197 if (priv == PRIV_MSGBUF) {
198 error = 0;
199 goto out;
200 }
201 }
202
203 /*
204 * Having determined if privilege is restricted by various policies,
205 * now determine if privilege is granted. At this point, any policy
206 * may grant privilege. For now, we allow short-circuit boolean
207 * evaluation, so may not call all policies. Perhaps we should.
208 *
209 * Superuser policy grants privilege based on the effective (or in
210 * the case of specific privileges, real) uid being 0. We allow the
211 * superuser policy to be globally disabled, although this is
212 * currenty of limited utility.
213 */
214 if (suser_enabled(cred)) {
215 switch (priv) {
216 case PRIV_MAXFILES:
217 case PRIV_MAXPROC:
218 case PRIV_PROC_LIMIT:
219 if (cred->cr_ruid == 0) {
220 error = 0;
221 goto out;
222 }
223 break;
224 case PRIV_VFS_READ_DIR:
225 /*
226 * Allow PRIV_VFS_READ_DIR for root if we're not in a
227 * jail, otherwise deny unless a MAC policy grants it.
228 */
229 if (jailed(cred))
230 break;
231 /* FALLTHROUGH */
232 default:
233 if (cred->cr_uid == 0) {
234 error = 0;
235 goto out;
236 }
237 break;
238 }
239 }
240
241 /*
242 * Writes to kernel/physical memory are a typical root-only operation,
243 * but non-root users are expected to be able to read it (provided they
244 * have permission to access /dev/[k]mem).
245 */
246 if (priv == PRIV_KMEM_READ) {
247 error = 0;
248 goto out;
249 }
250
251 /*
252 * Allow unprivileged process debugging on a per-jail basis.
253 * Do this here instead of prison_priv_check(), so it can also
254 * apply to prison0.
255 */
256 if (priv == PRIV_DEBUG_UNPRIV) {
257 if (prison_allow(cred, PR_ALLOW_UNPRIV_DEBUG)) {
258 error = 0;
259 goto out;
260 }
261 }
262
263 return (priv_check_cred_post(cred, priv, error, false));
264 out:
265 return (priv_check_cred_post(cred, priv, error, true));
266 }
267
268 int
priv_check(struct thread * td,int priv)269 priv_check(struct thread *td, int priv)
270 {
271
272 KASSERT(td == curthread, ("priv_check: td != curthread"));
273
274 return (priv_check_cred(td->td_ucred, priv));
275 }
276
277 static int __noinline
priv_check_cred_vfs_lookup_slow(struct ucred * cred)278 priv_check_cred_vfs_lookup_slow(struct ucred *cred)
279 {
280 int error;
281
282 error = priv_check_cred_pre(cred, PRIV_VFS_LOOKUP);
283 if (error)
284 goto out;
285
286 if (cred->cr_uid == 0 && suser_enabled(cred)) {
287 error = 0;
288 goto out;
289 }
290
291 return (priv_check_cred_post(cred, PRIV_VFS_LOOKUP, error, false));
292 out:
293 return (priv_check_cred_post(cred, PRIV_VFS_LOOKUP, error, true));
294
295 }
296
297 int
priv_check_cred_vfs_lookup(struct ucred * cred)298 priv_check_cred_vfs_lookup(struct ucred *cred)
299 {
300 int error;
301
302 if (__predict_false(mac_priv_check_fp_flag ||
303 mac_priv_grant_fp_flag || SDT_PROBES_ENABLED()))
304 return (priv_check_cred_vfs_lookup_slow(cred));
305
306 error = EPERM;
307 if (cred->cr_uid == 0 && suser_enabled(cred))
308 error = 0;
309 return (error);
310 }
311
312 int
priv_check_cred_vfs_lookup_nomac(struct ucred * cred)313 priv_check_cred_vfs_lookup_nomac(struct ucred *cred)
314 {
315 int error;
316
317 if (__predict_false(mac_priv_check_fp_flag ||
318 mac_priv_grant_fp_flag || SDT_PROBES_ENABLED()))
319 return (EAGAIN);
320
321 error = EPERM;
322 if (cred->cr_uid == 0 && suser_enabled(cred))
323 error = 0;
324 return (error);
325 }
326
327 static int __noinline
priv_check_cred_vfs_generation_slow(struct ucred * cred)328 priv_check_cred_vfs_generation_slow(struct ucred *cred)
329 {
330 int error;
331
332 error = priv_check_cred_pre(cred, PRIV_VFS_GENERATION);
333 if (error)
334 goto out;
335
336 if (jailed(cred)) {
337 error = EPERM;
338 goto out;
339 }
340
341 if (cred->cr_uid == 0 && suser_enabled(cred)) {
342 error = 0;
343 goto out;
344 }
345
346 return (priv_check_cred_post(cred, PRIV_VFS_GENERATION, error, false));
347 out:
348 return (priv_check_cred_post(cred, PRIV_VFS_GENERATION, error, true));
349
350 }
351
352 int
priv_check_cred_vfs_generation(struct ucred * cred)353 priv_check_cred_vfs_generation(struct ucred *cred)
354 {
355 int error;
356
357 if (__predict_false(mac_priv_check_fp_flag ||
358 mac_priv_grant_fp_flag || SDT_PROBES_ENABLED()))
359 return (priv_check_cred_vfs_generation_slow(cred));
360
361 error = EPERM;
362 if (!jailed(cred) && cred->cr_uid == 0 && suser_enabled(cred))
363 error = 0;
364 return (error);
365 }
366