FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_priv.c
1 /*-
2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
3 *
4 * Copyright (c) 2006 nCircle Network Security, Inc.
5 * Copyright (c) 2009 Robert N. M. Watson
6 * All rights reserved.
7 *
8 * This software was developed by Robert N. M. Watson for the TrustedBSD
9 * Project under contract to nCircle Network Security, Inc.
10 *
11 * Redistribution and use in source and binary forms, with or without
12 * modification, are permitted provided that the following conditions
13 * are met:
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.
19 *
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.
31 */
32
33 #include <sys/cdefs.h>
34 __FBSDID("$FreeBSD$");
35
36 #include <sys/param.h>
37 #include <sys/jail.h>
38 #include <sys/kernel.h>
39 #include <sys/priv.h>
40 #include <sys/proc.h>
41 #include <sys/sdt.h>
42 #include <sys/sysctl.h>
43 #include <sys/systm.h>
44
45 #include <security/mac/mac_framework.h>
46
47 /*
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
55 * the consequences.
56 */
57 static int suser_enabled = 1;
58 SYSCTL_INT(_security_bsd, OID_AUTO, suser_enabled, CTLFLAG_RWTUN,
59 &suser_enabled, 0, "processes with uid 0 have privilege");
60
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)");
64
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");
69
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");
73
74 /*
75 * Check a credential for privilege. Lots of good reasons to deny privilege;
76 * only a few to grant it.
77 */
78 int
79 priv_check_cred(struct ucred *cred, int priv, int flags)
80 {
81 int error;
82
83 KASSERT(PRIV_VALID(priv), ("priv_check_cred: invalid privilege %d",
84 priv));
85
86 /*
87 * We first evaluate policies that may deny the granting of
88 * privilege unilaterally.
89 */
90 #ifdef MAC
91 error = mac_priv_check(cred, priv);
92 if (error)
93 goto out;
94 #endif
95
96 /*
97 * Jail policy will restrict certain privileges that may otherwise be
98 * be granted.
99 */
100 error = prison_priv_check(cred, priv);
101 if (error)
102 goto out;
103
104 if (unprivileged_mlock) {
105 /*
106 * Allow unprivileged users to call mlock(2)/munlock(2) and
107 * mlockall(2)/munlockall(2).
108 */
109 switch (priv) {
110 case PRIV_VM_MLOCK:
111 case PRIV_VM_MUNLOCK:
112 error = 0;
113 goto out;
114 }
115 }
116
117 if (unprivileged_read_msgbuf) {
118 /*
119 * Allow an unprivileged user to read the kernel message
120 * buffer.
121 */
122 if (priv == PRIV_MSGBUF) {
123 error = 0;
124 goto out;
125 }
126 }
127
128 /*
129 * Having determined if privilege is restricted by various policies,
130 * now determine if privilege is granted. At this point, any policy
131 * may grant privilege. For now, we allow short-circuit boolean
132 * evaluation, so may not call all policies. Perhaps we should.
133 *
134 * Superuser policy grants privilege based on the effective (or in
135 * the case of specific privileges, real) uid being 0. We allow the
136 * superuser policy to be globally disabled, although this is
137 * currenty of limited utility.
138 */
139 if (suser_enabled) {
140 switch (priv) {
141 case PRIV_MAXFILES:
142 case PRIV_MAXPROC:
143 case PRIV_PROC_LIMIT:
144 if (cred->cr_ruid == 0) {
145 error = 0;
146 goto out;
147 }
148 break;
149 default:
150 if (cred->cr_uid == 0) {
151 error = 0;
152 goto out;
153 }
154 break;
155 }
156 }
157
158 /*
159 * Writes to kernel/physical memory are a typical root-only operation,
160 * but non-root users are expected to be able to read it (provided they
161 * have permission to access /dev/[k]mem).
162 */
163 if (priv == PRIV_KMEM_READ) {
164 error = 0;
165 goto out;
166 }
167
168 /*
169 * Now check with MAC, if enabled, to see if a policy module grants
170 * privilege.
171 */
172 #ifdef MAC
173 if (mac_priv_grant(cred, priv) == 0) {
174 error = 0;
175 goto out;
176 }
177 #endif
178
179 /*
180 * The default is deny, so if no policies have granted it, reject
181 * with a privilege error here.
182 */
183 error = EPERM;
184 out:
185 if (error)
186 SDT_PROBE1(priv, kernel, priv_check, priv__err, priv);
187 else
188 SDT_PROBE1(priv, kernel, priv_check, priv__ok, priv);
189 return (error);
190 }
191
192 int
193 priv_check(struct thread *td, int priv)
194 {
195
196 KASSERT(td == curthread, ("priv_check: td != curthread"));
197
198 return (priv_check_cred(td->td_ucred, priv, 0));
199 }
Cache object: 4ec103d424e727a7da08763e2a984645
|