2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
4 * Copyright (c) 2006 nCircle Network Security, Inc.
5 * Copyright (c) 2009 Robert N. M. Watson
8 * This software was developed by Robert N. M. Watson for the TrustedBSD
9 * Project under contract to nCircle Network Security, Inc.
11 * Redistribution and use in source and binary forms, with or without
12 * modification, are permitted provided that the following conditions
14 * 1. Redistributions of source code must retain the above copyright
15 * notice, this list of conditions and the following disclaimer.
16 * 2. Redistributions in binary form must reproduce the above copyright
17 * notice, this list of conditions and the following disclaimer in the
18 * documentation and/or other materials provided with the distribution.
20 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR, NCIRCLE NETWORK SECURITY,
24 * INC., OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
25 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
26 * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
27 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
28 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
29 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
30 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
33 #include <sys/cdefs.h>
34 __FBSDID("$FreeBSD$");
36 #include <sys/param.h>
38 #include <sys/kernel.h>
42 #include <sys/sysctl.h>
43 #include <sys/systm.h>
45 #include <security/mac/mac_framework.h>
48 * `suser_enabled' (which can be set by the security.bsd.suser_enabled
49 * sysctl) determines whether the system 'super-user' policy is in effect. If
50 * it is nonzero, an effective uid of 0 connotes special privilege,
51 * overriding many mandatory and discretionary protections. If it is zero,
52 * uid 0 is offered no special privilege in the kernel security policy.
53 * Setting it to zero may seriously impact the functionality of many existing
54 * userland programs, and should not be done without careful consideration of
57 static int __read_mostly suser_enabled = 1;
58 SYSCTL_INT(_security_bsd, OID_AUTO, suser_enabled, CTLFLAG_RWTUN,
59 &suser_enabled, 0, "processes with uid 0 have privilege");
61 static int unprivileged_mlock = 1;
62 SYSCTL_INT(_security_bsd, OID_AUTO, unprivileged_mlock, CTLFLAG_RWTUN,
63 &unprivileged_mlock, 0, "Allow non-root users to call mlock(2)");
65 static int unprivileged_read_msgbuf = 1;
66 SYSCTL_INT(_security_bsd, OID_AUTO, unprivileged_read_msgbuf,
67 CTLFLAG_RW, &unprivileged_read_msgbuf, 0,
68 "Unprivileged processes may read the kernel message buffer");
70 SDT_PROVIDER_DEFINE(priv);
71 SDT_PROBE_DEFINE1(priv, kernel, priv_check, priv__ok, "int");
72 SDT_PROBE_DEFINE1(priv, kernel, priv_check, priv__err, "int");
74 static __always_inline int
75 priv_check_cred_pre(struct ucred *cred, int priv)
80 error = mac_priv_check(cred, priv);
87 static __always_inline int
88 priv_check_cred_post(struct ucred *cred, int priv, int error, bool handled)
91 if (__predict_true(handled))
94 * Now check with MAC, if enabled, to see if a policy module grants
98 if (mac_priv_grant(cred, priv) == 0) {
105 * The default is deny, so if no policies have granted it, reject
106 * with a privilege error here.
110 if (SDT_PROBES_ENABLED()) {
112 SDT_PROBE1(priv, kernel, priv_check, priv__err, priv);
114 SDT_PROBE1(priv, kernel, priv_check, priv__ok, priv);
120 * Check a credential for privilege. Lots of good reasons to deny privilege;
121 * only a few to grant it.
124 priv_check_cred(struct ucred *cred, int priv)
128 KASSERT(PRIV_VALID(priv), ("priv_check_cred: invalid privilege %d",
132 case PRIV_VFS_GENERATION:
133 return (priv_check_cred_vfs_generation(cred));
137 * We first evaluate policies that may deny the granting of
138 * privilege unilaterally.
140 error = priv_check_cred_pre(cred, priv);
145 * Jail policy will restrict certain privileges that may otherwise be
148 error = prison_priv_check(cred, priv);
152 if (unprivileged_mlock) {
154 * Allow unprivileged users to call mlock(2)/munlock(2) and
155 * mlockall(2)/munlockall(2).
159 case PRIV_VM_MUNLOCK:
165 if (unprivileged_read_msgbuf) {
167 * Allow an unprivileged user to read the kernel message
170 if (priv == PRIV_MSGBUF) {
177 * Having determined if privilege is restricted by various policies,
178 * now determine if privilege is granted. At this point, any policy
179 * may grant privilege. For now, we allow short-circuit boolean
180 * evaluation, so may not call all policies. Perhaps we should.
182 * Superuser policy grants privilege based on the effective (or in
183 * the case of specific privileges, real) uid being 0. We allow the
184 * superuser policy to be globally disabled, although this is
185 * currenty of limited utility.
191 case PRIV_PROC_LIMIT:
192 if (cred->cr_ruid == 0) {
197 case PRIV_VFS_READ_DIR:
199 * Allow PRIV_VFS_READ_DIR for root if we're not in a
200 * jail, otherwise deny unless a MAC policy grants it.
206 if (cred->cr_uid == 0) {
215 * Writes to kernel/physical memory are a typical root-only operation,
216 * but non-root users are expected to be able to read it (provided they
217 * have permission to access /dev/[k]mem).
219 if (priv == PRIV_KMEM_READ) {
225 * Allow unprivileged process debugging on a per-jail basis.
226 * Do this here instead of prison_priv_check(), so it can also
229 if (priv == PRIV_DEBUG_UNPRIV) {
230 if (prison_allow(cred, PR_ALLOW_UNPRIV_DEBUG)) {
236 return (priv_check_cred_post(cred, priv, error, false));
238 return (priv_check_cred_post(cred, priv, error, true));
242 priv_check(struct thread *td, int priv)
245 KASSERT(td == curthread, ("priv_check: td != curthread"));
247 return (priv_check_cred(td->td_ucred, priv));
251 priv_check_cred_vfs_generation(struct ucred *cred)
255 error = priv_check_cred_pre(cred, PRIV_VFS_GENERATION);
264 if (cred->cr_uid == 0 && suser_enabled) {
269 return (priv_check_cred_post(cred, PRIV_VFS_GENERATION, error, false));
271 return (priv_check_cred_post(cred, PRIV_VFS_GENERATION, error, true));