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/param.h>
35 #include <sys/jail.h>
36 #include <sys/kernel.h>
37 #include <sys/lock.h>
38 #include <sys/mutex.h>
39 #include <sys/sx.h>
40 #include <sys/priv.h>
41 #include <sys/proc.h>
42 #include <sys/sdt.h>
43 #include <sys/sysctl.h>
44 #include <sys/systm.h>
45
46 #include <security/mac/mac_framework.h>
47
48 /*
49 * `suser_enabled' (which can be set by the security.bsd.suser_enabled
50 * sysctl) determines whether the system 'super-user' policy is in effect. If
51 * it is nonzero, an effective uid of 0 connotes special privilege,
52 * overriding many mandatory and discretionary protections. If it is zero,
53 * uid 0 is offered no special privilege in the kernel security policy.
54 * Setting it to zero may seriously impact the functionality of many existing
55 * userland programs, and should not be done without careful consideration of
56 * the consequences.
57 */
58
59 static bool
suser_enabled(struct ucred * cred)60 suser_enabled(struct ucred *cred)
61 {
62
63 return (prison_allow(cred, PR_ALLOW_SUSER));
64 }
65
66 static int
sysctl_kern_suser_enabled(SYSCTL_HANDLER_ARGS)67 sysctl_kern_suser_enabled(SYSCTL_HANDLER_ARGS)
68 {
69 struct ucred *cred;
70 int error, enabled;
71
72 cred = req->td->td_ucred;
73 enabled = suser_enabled(cred);
74 error = sysctl_handle_int(oidp, &enabled, 0, req);
75 if (error || !req->newptr)
76 return (error);
77 prison_set_allow(cred, PR_ALLOW_SUSER, enabled);
78 return (0);
79 }
80
81 SYSCTL_PROC(_security_bsd, OID_AUTO, suser_enabled, CTLTYPE_INT |
82 CTLFLAG_RWTUN | CTLFLAG_PRISON | CTLFLAG_MPSAFE, 0, 0,
83 &sysctl_kern_suser_enabled, "I", "Processes with uid 0 have privilege");
84
85 static int unprivileged_mlock = 1;
86 SYSCTL_INT(_security_bsd, OID_AUTO, unprivileged_mlock, CTLFLAG_RWTUN,
87 &unprivileged_mlock, 0, "Allow non-root users to call mlock(2)");
88
89 static int unprivileged_read_msgbuf = 1;
90 SYSCTL_INT(_security_bsd, OID_AUTO, unprivileged_read_msgbuf,
91 CTLFLAG_RW, &unprivileged_read_msgbuf, 0,
92 "Unprivileged processes may read the kernel message buffer");
93
94 SDT_PROVIDER_DEFINE(priv);
95 SDT_PROBE_DEFINE1(priv, kernel, priv_check, priv__ok, "int");
96 SDT_PROBE_DEFINE1(priv, kernel, priv_check, priv__err, "int");
97
98 static __always_inline int
priv_check_cred_pre(struct ucred * cred,int priv)99 priv_check_cred_pre(struct ucred *cred, int priv)
100 {
101 int error;
102
103 #ifdef MAC
104 error = mac_priv_check(cred, priv);
105 #else
106 error = 0;
107 #endif
108 return (error);
109 }
110
111 static __always_inline int
priv_check_cred_post(struct ucred * cred,int priv,int error,bool handled)112 priv_check_cred_post(struct ucred *cred, int priv, int error, bool handled)
113 {
114
115 if (__predict_true(handled))
116 goto out;
117 /*
118 * Now check with MAC, if enabled, to see if a policy module grants
119 * privilege.
120 */
121 #ifdef MAC
122 if (mac_priv_grant(cred, priv) == 0) {
123 error = 0;
124 goto out;
125 }
126 #endif
127
128 /*
129 * The default is deny, so if no policies have granted it, reject
130 * with a privilege error here.
131 */
132 error = EPERM;
133 out:
134 if (SDT_PROBES_ENABLED()) {
135 if (error)
136 SDT_PROBE1(priv, kernel, priv_check, priv__err, priv);
137 else
138 SDT_PROBE1(priv, kernel, priv_check, priv__ok, priv);
139 }
140 return (error);
141 }
142
143 /*
144 * Check a credential for privilege. Lots of good reasons to deny privilege;
145 * only a few to grant it.
146 */
147 int
priv_check_cred(struct ucred * cred,int priv)148 priv_check_cred(struct ucred *cred, int priv)
149 {
150 int error;
151
152 KASSERT(PRIV_VALID(priv), ("priv_check_cred: invalid privilege %d",
153 priv));
154
155 switch (priv) {
156 case PRIV_VFS_LOOKUP:
157 return (priv_check_cred_vfs_lookup(cred));
158 case PRIV_VFS_GENERATION:
159 return (priv_check_cred_vfs_generation(cred));
160 }
161
162 /*
163 * We first evaluate policies that may deny the granting of
164 * privilege unilaterally.
165 */
166 error = priv_check_cred_pre(cred, priv);
167 if (error)
168 goto out;
169
170 /*
171 * Jail policy will restrict certain privileges that may otherwise be
172 * be granted.
173 */
174 error = prison_priv_check(cred, priv);
175 if (error)
176 goto out;
177
178 if (unprivileged_mlock) {
179 /*
180 * Allow unprivileged users to call mlock(2)/munlock(2) and
181 * mlockall(2)/munlockall(2).
182 */
183 switch (priv) {
184 case PRIV_VM_MLOCK:
185 case PRIV_VM_MUNLOCK:
186 error = 0;
187 goto out;
188 }
189 }
190
191 if (unprivileged_read_msgbuf) {
192 /*
193 * Allow an unprivileged user to read the kernel message
194 * buffer.
195 */
196 if (priv == PRIV_MSGBUF) {
197 error = 0;
198 goto out;
199 }
200 }
201
202 /*
203 * Having determined if privilege is restricted by various policies,
204 * now determine if privilege is granted. At this point, any policy
205 * may grant privilege. For now, we allow short-circuit boolean
206 * evaluation, so may not call all policies. Perhaps we should.
207 *
208 * Superuser policy grants privilege based on the effective (or in
209 * the case of specific privileges, real) uid being 0. We allow the
210 * superuser policy to be globally disabled, although this is
211 * currenty of limited utility.
212 */
213 if (suser_enabled(cred)) {
214 switch (priv) {
215 case PRIV_MAXFILES:
216 case PRIV_MAXPROC:
217 case PRIV_PROC_LIMIT:
218 if (cred->cr_ruid == 0) {
219 error = 0;
220 goto out;
221 }
222 break;
223 case PRIV_VFS_READ_DIR:
224 /*
225 * Allow PRIV_VFS_READ_DIR for root if we're not in a
226 * jail, otherwise deny unless a MAC policy grants it.
227 */
228 if (jailed(cred))
229 break;
230 /* FALLTHROUGH */
231 default:
232 if (cred->cr_uid == 0) {
233 error = 0;
234 goto out;
235 }
236 break;
237 }
238 }
239
240 /*
241 * Writes to kernel/physical memory are a typical root-only operation,
242 * but non-root users are expected to be able to read it (provided they
243 * have permission to access /dev/[k]mem).
244 */
245 if (priv == PRIV_KMEM_READ) {
246 error = 0;
247 goto out;
248 }
249
250 /*
251 * Allow unprivileged process debugging on a per-jail basis.
252 * Do this here instead of prison_priv_check(), so it can also
253 * apply to prison0.
254 */
255 if (priv == PRIV_DEBUG_UNPRIV) {
256 if (prison_allow(cred, PR_ALLOW_UNPRIV_DEBUG)) {
257 error = 0;
258 goto out;
259 }
260 }
261
262 return (priv_check_cred_post(cred, priv, error, false));
263 out:
264 return (priv_check_cred_post(cred, priv, error, true));
265 }
266
267 int
priv_check(struct thread * td,int priv)268 priv_check(struct thread *td, int priv)
269 {
270
271 KASSERT(td == curthread, ("priv_check: td != curthread"));
272
273 return (priv_check_cred(td->td_ucred, priv));
274 }
275
276 static int __noinline
priv_check_cred_vfs_lookup_slow(struct ucred * cred)277 priv_check_cred_vfs_lookup_slow(struct ucred *cred)
278 {
279 int error;
280
281 error = priv_check_cred_pre(cred, PRIV_VFS_LOOKUP);
282 if (error)
283 goto out;
284
285 if (cred->cr_uid == 0 && suser_enabled(cred)) {
286 error = 0;
287 goto out;
288 }
289
290 return (priv_check_cred_post(cred, PRIV_VFS_LOOKUP, error, false));
291 out:
292 return (priv_check_cred_post(cred, PRIV_VFS_LOOKUP, error, true));
293
294 }
295
296 int
priv_check_cred_vfs_lookup(struct ucred * cred)297 priv_check_cred_vfs_lookup(struct ucred *cred)
298 {
299 int error;
300
301 if (__predict_false(mac_priv_check_fp_flag ||
302 mac_priv_grant_fp_flag || SDT_PROBES_ENABLED()))
303 return (priv_check_cred_vfs_lookup_slow(cred));
304
305 error = EPERM;
306 if (cred->cr_uid == 0 && suser_enabled(cred))
307 error = 0;
308 return (error);
309 }
310
311 int
priv_check_cred_vfs_lookup_nomac(struct ucred * cred)312 priv_check_cred_vfs_lookup_nomac(struct ucred *cred)
313 {
314 int error;
315
316 if (__predict_false(mac_priv_check_fp_flag ||
317 mac_priv_grant_fp_flag || SDT_PROBES_ENABLED()))
318 return (EAGAIN);
319
320 error = EPERM;
321 if (cred->cr_uid == 0 && suser_enabled(cred))
322 error = 0;
323 return (error);
324 }
325
326 static int __noinline
priv_check_cred_vfs_generation_slow(struct ucred * cred)327 priv_check_cred_vfs_generation_slow(struct ucred *cred)
328 {
329 int error;
330
331 error = priv_check_cred_pre(cred, PRIV_VFS_GENERATION);
332 if (error)
333 goto out;
334
335 if (jailed(cred)) {
336 error = EPERM;
337 goto out;
338 }
339
340 if (cred->cr_uid == 0 && suser_enabled(cred)) {
341 error = 0;
342 goto out;
343 }
344
345 return (priv_check_cred_post(cred, PRIV_VFS_GENERATION, error, false));
346 out:
347 return (priv_check_cred_post(cred, PRIV_VFS_GENERATION, error, true));
348
349 }
350
351 int
priv_check_cred_vfs_generation(struct ucred * cred)352 priv_check_cred_vfs_generation(struct ucred *cred)
353 {
354 int error;
355
356 if (__predict_false(mac_priv_check_fp_flag ||
357 mac_priv_grant_fp_flag || SDT_PROBES_ENABLED()))
358 return (priv_check_cred_vfs_generation_slow(cred));
359
360 error = EPERM;
361 if (!jailed(cred) && cred->cr_uid == 0 && suser_enabled(cred))
362 error = 0;
363 return (error);
364 }
365