FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_priv.c
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 "opt_kdtrace.h"
32
33 #include <sys/cdefs.h>
34 __FBSDID("$FreeBSD: releng/8.1/sys/kern/kern_priv.c 199583 2009-11-20 15:27:52Z jhb $");
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_RW,
59 &suser_enabled, 0, "processes with uid 0 have privilege");
60 TUNABLE_INT("security.bsd.suser_enabled", &suser_enabled);
61
62 SDT_PROVIDER_DEFINE(priv);
63 SDT_PROBE_DEFINE1(priv, kernel, priv_check, priv_ok, "int");
64 SDT_PROBE_DEFINE1(priv, kernel, priv_check, priv_err, "int");
65
66 /*
67 * Check a credential for privilege. Lots of good reasons to deny privilege;
68 * only a few to grant it.
69 */
70 int
71 priv_check_cred(struct ucred *cred, int priv, int flags)
72 {
73 int error;
74
75 KASSERT(PRIV_VALID(priv), ("priv_check_cred: invalid privilege %d",
76 priv));
77
78 /*
79 * We first evaluate policies that may deny the granting of
80 * privilege unilaterally.
81 */
82 #ifdef MAC
83 error = mac_priv_check(cred, priv);
84 if (error)
85 goto out;
86 #endif
87
88 /*
89 * Jail policy will restrict certain privileges that may otherwise be
90 * be granted.
91 */
92 error = prison_priv_check(cred, priv);
93 if (error)
94 goto out;
95
96 /*
97 * Having determined if privilege is restricted by various policies,
98 * now determine if privilege is granted. At this point, any policy
99 * may grant privilege. For now, we allow short-circuit boolean
100 * evaluation, so may not call all policies. Perhaps we should.
101 *
102 * Superuser policy grants privilege based on the effective (or in
103 * the case of specific privileges, real) uid being 0. We allow the
104 * superuser policy to be globally disabled, although this is
105 * currenty of limited utility.
106 */
107 if (suser_enabled) {
108 switch (priv) {
109 case PRIV_MAXFILES:
110 case PRIV_MAXPROC:
111 case PRIV_PROC_LIMIT:
112 if (cred->cr_ruid == 0) {
113 error = 0;
114 goto out;
115 }
116 break;
117
118 default:
119 if (cred->cr_uid == 0) {
120 error = 0;
121 goto out;
122 }
123 break;
124 }
125 }
126
127 /*
128 * Now check with MAC, if enabled, to see if a policy module grants
129 * privilege.
130 */
131 #ifdef MAC
132 if (mac_priv_grant(cred, priv) == 0) {
133 error = 0;
134 goto out;
135 }
136 #endif
137
138 /*
139 * The default is deny, so if no policies have granted it, reject
140 * with a privilege error here.
141 */
142 error = EPERM;
143 out:
144 if (error) {
145 SDT_PROBE(priv, kernel, priv_check, priv_err, priv, 0, 0, 0,
146 0);
147 } else {
148 SDT_PROBE(priv, kernel, priv_check, priv_ok, priv, 0, 0, 0,
149 0);
150 }
151 return (error);
152 }
153
154 int
155 priv_check(struct thread *td, int priv)
156 {
157
158 KASSERT(td == curthread, ("priv_check: td != curthread"));
159
160 return (priv_check_cred(td->td_ucred, priv, 0));
161 }
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