1 /*-
2 * Copyright (c) 2006 nCircle Network Security, Inc.
3 * Copyright (c) 2009 Robert N. M. Watson
4 * All rights reserved.
5 *
6 * This software was developed by Robert N. M. Watson for the TrustedBSD
7 * Project under contract to nCircle Network Security, Inc.
8 *
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
11 * are met:
12 * 1. Redistributions of source code must retain the above copyright
13 * notice, this list of conditions and the following disclaimer.
14 * 2. Redistributions in binary form must reproduce the above copyright
15 * notice, this list of conditions and the following disclaimer in the
16 * documentation and/or other materials provided with the distribution.
17 *
18 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
19 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
20 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
21 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR, NCIRCLE NETWORK SECURITY,
22 * INC., OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
23 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
24 * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
25 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
26 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
27 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
28 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
29 */
30
31 #include <sys/cdefs.h>
32 __FBSDID("$FreeBSD$");
33
34 #include <sys/param.h>
35 #include <sys/jail.h>
36 #include <sys/kernel.h>
37 #include <sys/priv.h>
38 #include <sys/proc.h>
39 #include <sys/sdt.h>
40 #include <sys/sysctl.h>
41 #include <sys/systm.h>
42
43 #include <security/mac/mac_framework.h>
44
45 /*
46 * `suser_enabled' (which can be set by the security.bsd.suser_enabled
47 * sysctl) determines whether the system 'super-user' policy is in effect. If
48 * it is nonzero, an effective uid of 0 connotes special privilege,
49 * overriding many mandatory and discretionary protections. If it is zero,
50 * uid 0 is offered no special privilege in the kernel security policy.
51 * Setting it to zero may seriously impact the functionality of many existing
52 * userland programs, and should not be done without careful consideration of
53 * the consequences.
54 */
55 static int suser_enabled = 1;
56 SYSCTL_INT(_security_bsd, OID_AUTO, suser_enabled, CTLFLAG_RWTUN,
57 &suser_enabled, 0, "processes with uid 0 have privilege");
58
59 static int unprivileged_mlock = 1;
60 SYSCTL_INT(_security_bsd, OID_AUTO, unprivileged_mlock, CTLFLAG_RWTUN,
61 &unprivileged_mlock, 0, "Allow non-root users to call mlock(2)");
62
63 static int unprivileged_read_msgbuf = 1;
64 SYSCTL_INT(_security_bsd, OID_AUTO, unprivileged_read_msgbuf,
65 CTLFLAG_RW, &unprivileged_read_msgbuf, 0,
66 "Unprivileged processes may read the kernel message buffer");
67
68 SDT_PROVIDER_DEFINE(priv);
69 SDT_PROBE_DEFINE1(priv, kernel, priv_check, priv__ok, "int");
70 SDT_PROBE_DEFINE1(priv, kernel, priv_check, priv__err, "int");
71
72 /*
73 * Check a credential for privilege. Lots of good reasons to deny privilege;
74 * only a few to grant it.
75 */
76 int
priv_check_cred(struct ucred * cred,int priv,int flags)77 priv_check_cred(struct ucred *cred, int priv, int flags)
78 {
79 int error;
80
81 KASSERT(PRIV_VALID(priv), ("priv_check_cred: invalid privilege %d",
82 priv));
83
84 /*
85 * We first evaluate policies that may deny the granting of
86 * privilege unilaterally.
87 */
88 #ifdef MAC
89 error = mac_priv_check(cred, priv);
90 if (error)
91 goto out;
92 #endif
93
94 /*
95 * Jail policy will restrict certain privileges that may otherwise be
96 * be granted.
97 */
98 error = prison_priv_check(cred, priv);
99 if (error)
100 goto out;
101
102 if (unprivileged_mlock) {
103 /*
104 * Allow unprivileged users to call mlock(2)/munlock(2) and
105 * mlockall(2)/munlockall(2).
106 */
107 switch (priv) {
108 case PRIV_VM_MLOCK:
109 case PRIV_VM_MUNLOCK:
110 error = 0;
111 goto out;
112 }
113 }
114
115 if (unprivileged_read_msgbuf) {
116 /*
117 * Allow an unprivileged user to read the kernel message
118 * buffer.
119 */
120 if (priv == PRIV_MSGBUF) {
121 error = 0;
122 goto out;
123 }
124 }
125
126 /*
127 * Having determined if privilege is restricted by various policies,
128 * now determine if privilege is granted. At this point, any policy
129 * may grant privilege. For now, we allow short-circuit boolean
130 * evaluation, so may not call all policies. Perhaps we should.
131 *
132 * Superuser policy grants privilege based on the effective (or in
133 * the case of specific privileges, real) uid being 0. We allow the
134 * superuser policy to be globally disabled, although this is
135 * currenty of limited utility.
136 */
137 if (suser_enabled) {
138 switch (priv) {
139 case PRIV_MAXFILES:
140 case PRIV_MAXPROC:
141 case PRIV_PROC_LIMIT:
142 if (cred->cr_ruid == 0) {
143 error = 0;
144 goto out;
145 }
146 break;
147 default:
148 if (cred->cr_uid == 0) {
149 error = 0;
150 goto out;
151 }
152 break;
153 }
154 }
155
156 /*
157 * Writes to kernel/physical memory are a typical root-only operation,
158 * but non-root users are expected to be able to read it (provided they
159 * have permission to access /dev/[k]mem).
160 */
161 if (priv == PRIV_KMEM_READ) {
162 error = 0;
163 goto out;
164 }
165
166 /*
167 * Now check with MAC, if enabled, to see if a policy module grants
168 * privilege.
169 */
170 #ifdef MAC
171 if (mac_priv_grant(cred, priv) == 0) {
172 error = 0;
173 goto out;
174 }
175 #endif
176
177 /*
178 * The default is deny, so if no policies have granted it, reject
179 * with a privilege error here.
180 */
181 error = EPERM;
182 out:
183 if (error)
184 SDT_PROBE1(priv, kernel, priv_check, priv__err, priv);
185 else
186 SDT_PROBE1(priv, kernel, priv_check, priv__ok, priv);
187 return (error);
188 }
189
190 int
priv_check(struct thread * td,int priv)191 priv_check(struct thread *td, int priv)
192 {
193
194 KASSERT(td == curthread, ("priv_check: td != curthread"));
195
196 return (priv_check_cred(td->td_ucred, priv, 0));
197 }
198