FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_priv.c
1 /*-
2 * Copyright (c) 2006 nCircle Network Security, Inc.
3 * All rights reserved.
4 *
5 * This software was developed by Robert N. M. Watson for the TrustedBSD
6 * Project under contract to nCircle Network Security, Inc.
7 *
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
10 * are met:
11 * 1. Redistributions of source code must retain the above copyright
12 * notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 * notice, this list of conditions and the following disclaimer in the
15 * documentation and/or other materials provided with the distribution.
16 *
17 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR, NCIRCLE NETWORK SECURITY,
21 * INC., OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
22 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
23 * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
24 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
25 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
26 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
27 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
28 *
29 * $FreeBSD$
30 */
31
32 #include "opt_mac.h"
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/sysctl.h>
40 #include <sys/systm.h>
41
42 #include <security/mac/mac_framework.h>
43
44 /*
45 * `suser_enabled' (which can be set by the security.bsd.suser_enabled
46 * sysctl) determines whether the system 'super-user' policy is in effect. If
47 * it is nonzero, an effective uid of 0 connotes special privilege,
48 * overriding many mandatory and discretionary protections. If it is zero,
49 * uid 0 is offered no special privilege in the kernel security policy.
50 * Setting it to zero may seriously impact the functionality of many existing
51 * userland programs, and should not be done without careful consideration of
52 * the consequences.
53 */
54 static int suser_enabled = 1;
55 SYSCTL_INT(_security_bsd, OID_AUTO, suser_enabled, CTLFLAG_RW,
56 &suser_enabled, 0, "processes with uid 0 have privilege");
57 TUNABLE_INT("security.bsd.suser_enabled", &suser_enabled);
58
59 /*
60 * Check a credential for privilege. Lots of good reasons to deny privilege;
61 * only a few to grant it.
62 */
63 int
64 priv_check_cred(struct ucred *cred, int priv, int flags)
65 {
66 int error;
67
68 KASSERT(PRIV_VALID(priv), ("priv_check_cred: invalid privilege %d",
69 priv));
70
71 /*
72 * We first evaluate policies that may deny the granting of
73 * privilege unilaterally.
74 */
75 #ifdef MAC
76 error = mac_priv_check(cred, priv);
77 if (error)
78 return (error);
79 #endif
80
81 /*
82 * Jail policy will restrict certain privileges that may otherwise be
83 * be granted.
84 */
85 error = prison_priv_check(cred, priv);
86 if (error)
87 return (error);
88
89 /*
90 * Having determined if privilege is restricted by various policies,
91 * now determine if privilege is granted. At this point, any policy
92 * may grant privilege. For now, we allow short-circuit boolean
93 * evaluation, so may not call all policies. Perhaps we should.
94 *
95 * Superuser policy grants privilege based on the effective (or in
96 * the case of specific privileges, real) uid being 0. We allow the
97 * superuser policy to be globally disabled, although this is
98 * currenty of limited utility.
99 */
100 if (suser_enabled) {
101 switch (priv) {
102 case PRIV_MAXFILES:
103 case PRIV_MAXPROC:
104 case PRIV_PROC_LIMIT:
105 if (cred->cr_ruid == 0)
106 return (0);
107 break;
108
109 default:
110 if (cred->cr_uid == 0)
111 return (0);
112 break;
113 }
114 }
115
116 /*
117 * Now check with MAC, if enabled, to see if a policy module grants
118 * privilege.
119 */
120 #ifdef MAC
121 if (mac_priv_grant(cred, priv) == 0)
122 return (0);
123 #endif
124 return (EPERM);
125 }
126
127 int
128 priv_check(struct thread *td, int priv)
129 {
130
131 KASSERT(td == curthread, ("priv_check: td != curthread"));
132
133 return (priv_check_cred(td->td_ucred, priv, 0));
134 }
135
136 /*
137 * Historical suser() wrapper functions, which now simply request PRIV_ROOT.
138 * These will be removed in the near future, and exist solely because
139 * the kernel and modules are not yet fully adapted to the new model.
140 */
141 int
142 suser_cred(struct ucred *cred, int flags)
143 {
144
145 return (priv_check_cred(cred, PRIV_ROOT, flags));
146 }
147
148 int
149 suser(struct thread *td)
150 {
151
152 KASSERT(td == curthread, ("suser: td != curthread"));
153
154 return (suser_cred(td->td_ucred, 0));
155 }
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