kern_priv.c revision 176903 
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: head/sys/kern/kern_priv.c 176903 2008-03-07 15:27:08Z rwatson $");
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 */
55static int	suser_enabled = 1;
56SYSCTL_INT(_security_bsd, OID_AUTO, suser_enabled, CTLFLAG_RW,
57    &suser_enabled, 0, "processes with uid 0 have privilege");
58TUNABLE_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 */
64int
65priv_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
128int
129priv_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 */
142int
143suser_cred(struct ucred *cred, int flags)
144{
145
146	return (priv_check_cred(cred, PRIV_ROOT, flags));
147}
148
149int
150suser(struct thread *td)
151{
152
153	KASSERT(td == curthread, ("suser: td != curthread"));
154
155	return (suser_cred(td->td_ucred, 0));
156}
157