2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
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>
9 * This software was developed by Robert N. M. Watson for the TrustedBSD
10 * Project under contract to nCircle Network Security, Inc.
12 * Redistribution and use in source and binary forms, with or without
13 * modification, are permitted provided that the following conditions
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.
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.
34 #include <sys/cdefs.h>
35 __FBSDID("$FreeBSD$");
37 #include <sys/param.h>
39 #include <sys/kernel.h>
41 #include <sys/mutex.h>
46 #include <sys/sysctl.h>
47 #include <sys/systm.h>
49 #include <security/mac/mac_framework.h>
52 * `suser_enabled' (which can be set by the security.bsd.suser_enabled
53 * sysctl) determines whether the system 'super-user' policy is in effect. If
54 * it is nonzero, an effective uid of 0 connotes special privilege,
55 * overriding many mandatory and discretionary protections. If it is zero,
56 * uid 0 is offered no special privilege in the kernel security policy.
57 * Setting it to zero may seriously impact the functionality of many existing
58 * userland programs, and should not be done without careful consideration of
63 suser_enabled(struct ucred *cred)
66 return (prison_allow(cred, PR_ALLOW_SUSER) ? true : false);
70 prison_suser_set(struct prison *pr, int enabled)
74 pr->pr_allow |= PR_ALLOW_SUSER;
76 pr->pr_allow &= ~PR_ALLOW_SUSER;
81 sysctl_kern_suser_enabled(SYSCTL_HANDLER_ARGS)
83 struct prison *pr, *cpr;
85 int descend, error, enabled;
87 cred = req->td->td_ucred;
88 enabled = suser_enabled(cred);
90 error = sysctl_handle_int(oidp, &enabled, 0, req);
91 if (error || !req->newptr)
95 sx_slock(&allprison_lock);
96 mtx_lock(&pr->pr_mtx);
98 prison_suser_set(pr, enabled);
100 FOREACH_PRISON_DESCENDANT_LOCKED(pr, cpr, descend) {
101 prison_suser_set(cpr, 0);
104 mtx_unlock(&pr->pr_mtx);
105 sx_sunlock(&allprison_lock);
109 SYSCTL_PROC(_security_bsd, OID_AUTO, suser_enabled, CTLTYPE_INT |
110 CTLFLAG_RWTUN | CTLFLAG_PRISON | CTLFLAG_MPSAFE, 0, 0,
111 &sysctl_kern_suser_enabled, "I", "Processes with uid 0 have privilege");
113 static int unprivileged_mlock = 1;
114 SYSCTL_INT(_security_bsd, OID_AUTO, unprivileged_mlock, CTLFLAG_RWTUN,
115 &unprivileged_mlock, 0, "Allow non-root users to call mlock(2)");
117 static int unprivileged_read_msgbuf = 1;
118 SYSCTL_INT(_security_bsd, OID_AUTO, unprivileged_read_msgbuf,
119 CTLFLAG_RW, &unprivileged_read_msgbuf, 0,
120 "Unprivileged processes may read the kernel message buffer");
122 SDT_PROVIDER_DEFINE(priv);
123 SDT_PROBE_DEFINE1(priv, kernel, priv_check, priv__ok, "int");
124 SDT_PROBE_DEFINE1(priv, kernel, priv_check, priv__err, "int");
126 static __always_inline int
127 priv_check_cred_pre(struct ucred *cred, int priv)
132 error = mac_priv_check(cred, priv);
139 static __always_inline int
140 priv_check_cred_post(struct ucred *cred, int priv, int error, bool handled)
143 if (__predict_true(handled))
146 * Now check with MAC, if enabled, to see if a policy module grants
150 if (mac_priv_grant(cred, priv) == 0) {
157 * The default is deny, so if no policies have granted it, reject
158 * with a privilege error here.
162 if (SDT_PROBES_ENABLED()) {
164 SDT_PROBE1(priv, kernel, priv_check, priv__err, priv);
166 SDT_PROBE1(priv, kernel, priv_check, priv__ok, priv);
172 * Check a credential for privilege. Lots of good reasons to deny privilege;
173 * only a few to grant it.
176 priv_check_cred(struct ucred *cred, int priv)
180 KASSERT(PRIV_VALID(priv), ("priv_check_cred: invalid privilege %d",
184 case PRIV_VFS_LOOKUP:
185 return (priv_check_cred_vfs_lookup(cred));
186 case PRIV_VFS_GENERATION:
187 return (priv_check_cred_vfs_generation(cred));
191 * We first evaluate policies that may deny the granting of
192 * privilege unilaterally.
194 error = priv_check_cred_pre(cred, priv);
199 * Jail policy will restrict certain privileges that may otherwise be
202 error = prison_priv_check(cred, priv);
206 if (unprivileged_mlock) {
208 * Allow unprivileged users to call mlock(2)/munlock(2) and
209 * mlockall(2)/munlockall(2).
213 case PRIV_VM_MUNLOCK:
219 if (unprivileged_read_msgbuf) {
221 * Allow an unprivileged user to read the kernel message
224 if (priv == PRIV_MSGBUF) {
231 * Having determined if privilege is restricted by various policies,
232 * now determine if privilege is granted. At this point, any policy
233 * may grant privilege. For now, we allow short-circuit boolean
234 * evaluation, so may not call all policies. Perhaps we should.
236 * Superuser policy grants privilege based on the effective (or in
237 * the case of specific privileges, real) uid being 0. We allow the
238 * superuser policy to be globally disabled, although this is
239 * currenty of limited utility.
241 if (suser_enabled(cred)) {
245 case PRIV_PROC_LIMIT:
246 if (cred->cr_ruid == 0) {
251 case PRIV_VFS_READ_DIR:
253 * Allow PRIV_VFS_READ_DIR for root if we're not in a
254 * jail, otherwise deny unless a MAC policy grants it.
260 if (cred->cr_uid == 0) {
269 * Writes to kernel/physical memory are a typical root-only operation,
270 * but non-root users are expected to be able to read it (provided they
271 * have permission to access /dev/[k]mem).
273 if (priv == PRIV_KMEM_READ) {
279 * Allow unprivileged process debugging on a per-jail basis.
280 * Do this here instead of prison_priv_check(), so it can also
283 if (priv == PRIV_DEBUG_UNPRIV) {
284 if (prison_allow(cred, PR_ALLOW_UNPRIV_DEBUG)) {
290 return (priv_check_cred_post(cred, priv, error, false));
292 return (priv_check_cred_post(cred, priv, error, true));
296 priv_check(struct thread *td, int priv)
299 KASSERT(td == curthread, ("priv_check: td != curthread"));
301 return (priv_check_cred(td->td_ucred, priv));
304 static int __noinline
305 priv_check_cred_vfs_lookup_slow(struct ucred *cred)
309 error = priv_check_cred_pre(cred, PRIV_VFS_LOOKUP);
313 if (cred->cr_uid == 0 && suser_enabled(cred)) {
318 return (priv_check_cred_post(cred, PRIV_VFS_LOOKUP, error, false));
320 return (priv_check_cred_post(cred, PRIV_VFS_LOOKUP, error, true));
325 priv_check_cred_vfs_lookup(struct ucred *cred)
329 if (__predict_false(mac_priv_check_fp_flag ||
330 mac_priv_grant_fp_flag || SDT_PROBES_ENABLED()))
331 return (priv_check_cred_vfs_lookup_slow(cred));
334 if (cred->cr_uid == 0 && suser_enabled(cred))
340 priv_check_cred_vfs_lookup_nomac(struct ucred *cred)
344 if (__predict_false(mac_priv_check_fp_flag ||
345 mac_priv_grant_fp_flag || SDT_PROBES_ENABLED()))
349 if (cred->cr_uid == 0 && suser_enabled(cred))
354 static int __noinline
355 priv_check_cred_vfs_generation_slow(struct ucred *cred)
359 error = priv_check_cred_pre(cred, PRIV_VFS_GENERATION);
368 if (cred->cr_uid == 0 && suser_enabled(cred)) {
373 return (priv_check_cred_post(cred, PRIV_VFS_GENERATION, error, false));
375 return (priv_check_cred_post(cred, PRIV_VFS_GENERATION, error, true));
380 priv_check_cred_vfs_generation(struct ucred *cred)
384 if (__predict_false(mac_priv_check_fp_flag ||
385 mac_priv_grant_fp_flag || SDT_PROBES_ENABLED()))
386 return (priv_check_cred_vfs_generation_slow(cred));
389 if (!jailed(cred) && cred->cr_uid == 0 && suser_enabled(cred))