kern_priv.c revision 193511 
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: head/sys/kern/kern_priv.c 193511 2009-06-05 14:55:22Z rwatson $");
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 */
57static int	suser_enabled = 1;
58SYSCTL_INT(_security_bsd, OID_AUTO, suser_enabled, CTLFLAG_RW,
59    &suser_enabled, 0, "processes with uid 0 have privilege");
60TUNABLE_INT("security.bsd.suser_enabled", &suser_enabled);
61
62SDT_PROVIDER_DEFINE(priv);
63SDT_PROBE_DEFINE1(priv, kernel, priv_check, priv_ok, "int");
64SDT_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 */
70int
71priv_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;
143out:
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
154int
155priv_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}
162