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 <sys/cdefs.h>
32 __FBSDID("$FreeBSD: releng/11.1/sys/kern/kern_priv.c 267992 2014-06-28 03:56:17Z hselasky $");
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 SDT_PROVIDER_DEFINE(priv);
64 SDT_PROBE_DEFINE1(priv, kernel, priv_check, priv__ok, "int");
65 SDT_PROBE_DEFINE1(priv, kernel, priv_check, priv__err, "int");
66
67 /*
68 * Check a credential for privilege. Lots of good reasons to deny privilege;
69 * only a few to grant it.
70 */
71 int
72 priv_check_cred(struct ucred *cred, int priv, int flags)
73 {
74 int error;
75
76 KASSERT(PRIV_VALID(priv), ("priv_check_cred: invalid privilege %d",
77 priv));
78
79 /*
80 * We first evaluate policies that may deny the granting of
81 * privilege unilaterally.
82 */
83 #ifdef MAC
84 error = mac_priv_check(cred, priv);
85 if (error)
86 goto out;
87 #endif
88
89 /*
90 * Jail policy will restrict certain privileges that may otherwise be
91 * be granted.
92 */
93 error = prison_priv_check(cred, priv);
94 if (error)
95 goto out;
96
97 if (unprivileged_mlock) {
98 /*
99 * Allow unprivileged users to call mlock(2)/munlock(2) and
100 * mlockall(2)/munlockall(2).
101 */
102 switch (priv) {
103 case PRIV_VM_MLOCK:
104 case PRIV_VM_MUNLOCK:
105 error = 0;
106 goto out;
107 }
108 }
109
110 /*
111 * Having determined if privilege is restricted by various policies,
112 * now determine if privilege is granted. At this point, any policy
113 * may grant privilege. For now, we allow short-circuit boolean
114 * evaluation, so may not call all policies. Perhaps we should.
115 *
116 * Superuser policy grants privilege based on the effective (or in
117 * the case of specific privileges, real) uid being 0. We allow the
118 * superuser policy to be globally disabled, although this is
119 * currenty of limited utility.
120 */
121 if (suser_enabled) {
122 switch (priv) {
123 case PRIV_MAXFILES:
124 case PRIV_MAXPROC:
125 case PRIV_PROC_LIMIT:
126 if (cred->cr_ruid == 0) {
127 error = 0;
128 goto out;
129 }
130 break;
131 default:
132 if (cred->cr_uid == 0) {
133 error = 0;
134 goto out;
135 }
136 break;
137 }
138 }
139
140 /*
141 * Writes to kernel/physical memory are a typical root-only operation,
142 * but non-root users are expected to be able to read it (provided they
143 * have permission to access /dev/[k]mem).
144 */
145 if (priv == PRIV_KMEM_READ) {
146 error = 0;
147 goto out;
148 }
149
150 /*
151 * Now check with MAC, if enabled, to see if a policy module grants
152 * privilege.
153 */
154 #ifdef MAC
155 if (mac_priv_grant(cred, priv) == 0) {
156 error = 0;
157 goto out;
158 }
159 #endif
160
161 /*
162 * The default is deny, so if no policies have granted it, reject
163 * with a privilege error here.
164 */
165 error = EPERM;
166 out:
167 if (error)
168 SDT_PROBE1(priv, kernel, priv_check, priv__err, priv);
169 else
170 SDT_PROBE1(priv, kernel, priv_check, priv__ok, priv);
171 return (error);
172 }
173
174 int
175 priv_check(struct thread *td, int priv)
176 {
177
178 KASSERT(td == curthread, ("priv_check: td != curthread"));
179
180 return (priv_check_cred(td->td_ucred, priv, 0));
181 }
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