kern_priv.c revision 170587 
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: head/sys/kern/kern_priv.c 170587 2007-06-12 00:12:01Z rwatson $
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 */
54int	suser_enabled = 1;
55SYSCTL_INT(_security_bsd, OID_AUTO, suser_enabled, CTLFLAG_RW,
56    &suser_enabled, 0, "processes with uid 0 have privilege");
57TUNABLE_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 */
63int
64priv_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#ifdef MAC
72	error = mac_priv_check(cred, priv);
73	if (error)
74		return (error);
75#endif
76
77	/*
78	 * Jail policy will restrict certain privileges that may otherwise be
79	 * be granted.
80	 */
81	error = prison_priv_check(cred, priv);
82	if (error)
83		return (error);
84
85	/*
86	 * Having determined if privilege is restricted by various policies,
87	 * now determine if privilege is granted.  For now, we allow
88	 * short-circuit boolean evaluation, so may not call all policies.
89	 * Perhaps we should.
90	 *
91	 * Superuser policy grants privilege based on the effective (or in
92	 * certain edge cases, real) uid being 0.  We allow the policy to be
93	 * globally disabled, although this is currently of limited utility.
94	 */
95	if (suser_enabled) {
96		if (flags & SUSER_RUID) {
97			if (cred->cr_ruid == 0)
98				return (0);
99		} else {
100			if (cred->cr_uid == 0)
101				return (0);
102		}
103	}
104
105	/*
106	 * Now check with MAC, if enabled, to see if a policy module grants
107	 * privilege.
108	 */
109#ifdef MAC
110	if (mac_priv_grant(cred, priv) == 0)
111		return (0);
112#endif
113	return (EPERM);
114}
115
116int
117priv_check(struct thread *td, int priv)
118{
119
120	KASSERT(td == curthread, ("priv_check: td != curthread"));
121
122	return (priv_check_cred(td->td_ucred, priv, 0));
123}
124
125/*
126 * Historical suser() wrapper functions, which now simply request PRIV_ROOT.
127 * These will be removed in the near future, and exist solely because
128 * the kernel and modules are not yet fully adapted to the new model.
129 */
130int
131suser_cred(struct ucred *cred, int flags)
132{
133
134	return (priv_check_cred(cred, PRIV_ROOT, flags));
135}
136
137int
138suser(struct thread *td)
139{
140
141	KASSERT(td == curthread, ("suser: td != curthread"));
142
143	return (suser_cred(td->td_ucred, 0));
144}
145