kern_priv.c revision 189063 
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#include "opt_mac.h"
33
34#include <sys/cdefs.h>
35__FBSDID("$FreeBSD: head/sys/kern/kern_priv.c 189063 2009-02-26 10:56:13Z rwatson $");
36
37#include <sys/param.h>
38#include <sys/jail.h>
39#include <sys/kernel.h>
40#include <sys/priv.h>
41#include <sys/proc.h>
42#include <sys/sdt.h>
43#include <sys/sysctl.h>
44#include <sys/systm.h>
45
46#include <security/mac/mac_framework.h>
47
48/*
49 * `suser_enabled' (which can be set by the security.bsd.suser_enabled
50 * sysctl) determines whether the system 'super-user' policy is in effect.  If
51 * it is nonzero, an effective uid of 0 connotes special privilege,
52 * overriding many mandatory and discretionary protections.  If it is zero,
53 * uid 0 is offered no special privilege in the kernel security policy.
54 * Setting it to zero may seriously impact the functionality of many existing
55 * userland programs, and should not be done without careful consideration of
56 * the consequences.
57 */
58static int	suser_enabled = 1;
59SYSCTL_INT(_security_bsd, OID_AUTO, suser_enabled, CTLFLAG_RW,
60    &suser_enabled, 0, "processes with uid 0 have privilege");
61TUNABLE_INT("security.bsd.suser_enabled", &suser_enabled);
62
63SDT_PROVIDER_DEFINE(priv);
64
65SDT_PROBE_DEFINE(priv, kernel, priv_check, priv_ok);
66SDT_PROBE_ARGTYPE(priv, kernel, priv_check, priv_ok, 0, "int");
67
68SDT_PROBE_DEFINE(priv, kernel, priv_check, priv_err);
69SDT_PROBE_ARGTYPE(priv, kernel, priv_check, priv_err, 0, "int");
70
71/*
72 * Check a credential for privilege.  Lots of good reasons to deny privilege;
73 * only a few to grant it.
74 */
75int
76priv_check_cred(struct ucred *cred, int priv, int flags)
77{
78	int error;
79
80	KASSERT(PRIV_VALID(priv), ("priv_check_cred: invalid privilege %d",
81	    priv));
82
83	/*
84	 * We first evaluate policies that may deny the granting of
85	 * privilege unilaterally.
86	 */
87#ifdef MAC
88	error = mac_priv_check(cred, priv);
89	if (error)
90		goto out;
91#endif
92
93	/*
94	 * Jail policy will restrict certain privileges that may otherwise be
95	 * be granted.
96	 */
97	error = prison_priv_check(cred, priv);
98	if (error)
99		goto out;
100
101	/*
102	 * Having determined if privilege is restricted by various policies,
103	 * now determine if privilege is granted.  At this point, any policy
104	 * may grant privilege.  For now, we allow short-circuit boolean
105	 * evaluation, so may not call all policies.  Perhaps we should.
106	 *
107	 * Superuser policy grants privilege based on the effective (or in
108	 * the case of specific privileges, real) uid being 0.  We allow the
109	 * superuser policy to be globally disabled, although this is
110	 * currenty of limited utility.
111	 */
112	if (suser_enabled) {
113		switch (priv) {
114		case PRIV_MAXFILES:
115		case PRIV_MAXPROC:
116		case PRIV_PROC_LIMIT:
117			if (cred->cr_ruid == 0) {
118				error = 0;
119				goto out;
120			}
121			break;
122
123		default:
124			if (cred->cr_uid == 0) {
125				error = 0;
126				goto out;
127			}
128			break;
129		}
130	}
131
132	/*
133	 * Now check with MAC, if enabled, to see if a policy module grants
134	 * privilege.
135	 */
136#ifdef MAC
137	if (mac_priv_grant(cred, priv) == 0) {
138		error = 0;
139		goto out;
140	}
141#endif
142
143	/*
144	 * The default is deny, so if no policies have granted it, reject
145	 * with a privilege error here.
146	 */
147	error = EPERM;
148out:
149	if (error) {
150		SDT_PROBE(priv, kernel, priv_check, priv_err, priv, 0, 0, 0,
151		    0);
152	} else {
153		SDT_PROBE(priv, kernel, priv_check, priv_ok, priv, 0, 0, 0,
154		    0);
155	}
156	return (error);
157}
158
159int
160priv_check(struct thread *td, int priv)
161{
162
163	KASSERT(td == curthread, ("priv_check: td != curthread"));
164
165	return (priv_check_cred(td->td_ucred, priv, 0));
166}
167