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
30 #include "opt_mac.h"
31
32 #include <sys/cdefs.h>
33 __FBSDID("$FreeBSD$");
34
35 #include <sys/param.h>
36 #include <sys/jail.h>
37 #include <sys/kernel.h>
38 #include <sys/priv.h>
39 #include <sys/proc.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_RW,
57 &suser_enabled, 0, "processes with uid 0 have privilege");
58 TUNABLE_INT("security.bsd.suser_enabled", &suser_enabled);
59
60 /*
61 * Check a credential for privilege. Lots of good reasons to deny privilege;
62 * only a few to grant it.
63 */
64 int
65 priv_check_cred(struct ucred *cred, int priv, int flags)
66 {
67 int error;
68
69 KASSERT(PRIV_VALID(priv), ("priv_check_cred: invalid privilege %d",
70 priv));
71
72 /*
73 * We first evaluate policies that may deny the granting of
74 * privilege unilaterally.
75 */
76 #ifdef MAC
77 error = mac_priv_check(cred, priv);
78 if (error)
79 return (error);
80 #endif
81
82 /*
83 * Jail policy will restrict certain privileges that may otherwise be
84 * be granted.
85 */
86 error = prison_priv_check(cred, priv);
87 if (error)
88 return (error);
89
90 /*
91 * Having determined if privilege is restricted by various policies,
92 * now determine if privilege is granted. At this point, any policy
93 * may grant privilege. For now, we allow short-circuit boolean
94 * evaluation, so may not call all policies. Perhaps we should.
95 *
96 * Superuser policy grants privilege based on the effective (or in
97 * the case of specific privileges, real) uid being 0. We allow the
98 * superuser policy to be globally disabled, although this is
99 * currenty of limited utility.
100 */
101 if (suser_enabled) {
102 switch (priv) {
103 case PRIV_MAXFILES:
104 case PRIV_MAXPROC:
105 case PRIV_PROC_LIMIT:
106 if (cred->cr_ruid == 0)
107 return (0);
108 break;
109
110 default:
111 if (cred->cr_uid == 0)
112 return (0);
113 break;
114 }
115 }
116
117 /*
118 * Now check with MAC, if enabled, to see if a policy module grants
119 * privilege.
120 */
121 #ifdef MAC
122 if (mac_priv_grant(cred, priv) == 0)
123 return (0);
124 #endif
125 return (EPERM);
126 }
127
128 int
129 priv_check(struct thread *td, int priv)
130 {
131
132 KASSERT(td == curthread, ("priv_check: td != curthread"));
133
134 return (priv_check_cred(td->td_ucred, priv, 0));
135 }
136
137 /*
138 * Historical suser() wrapper functions, which now simply request PRIV_ROOT.
139 * These will be removed in the near future, and exist solely because
140 * the kernel and modules are not yet fully adapted to the new model.
141 */
142 int
143 suser_cred(struct ucred *cred, int flags)
144 {
145
146 return (priv_check_cred(cred, PRIV_ROOT, flags));
147 }
148
149 int
150 suser(struct thread *td)
151 {
152
153 KASSERT(td == curthread, ("suser: td != curthread"));
154
155 return (suser_cred(td->td_ucred, 0));
156 }
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