kern_priv.c revision 252841 
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 252841 2013-07-05 21:31:16Z jamie $");
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
62static int	unprivileged_mlock = 1;
63SYSCTL_INT(_security_bsd, OID_AUTO, unprivileged_mlock, CTLFLAG_RW|CTLFLAG_TUN,
64    &unprivileged_mlock, 0, "Allow non-root users to call mlock(2)");
65TUNABLE_INT("security.bsd.unprivileged_mlock", &unprivileged_mlock);
66
67SDT_PROVIDER_DEFINE(priv);
68SDT_PROBE_DEFINE1(priv, kernel, priv_check, priv_ok, priv-ok, "int");
69SDT_PROBE_DEFINE1(priv, kernel, priv_check, priv_err, priv-err, "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	if (unprivileged_mlock) {
102		/*
103		 * Allow unprivileged users to call mlock(2)/munlock(2) and
104		 * mlockall(2)/munlockall(2).
105		 */
106		switch (priv) {
107		case PRIV_VM_MLOCK:
108		case PRIV_VM_MUNLOCK:
109			error = 0;
110			goto out;
111		}
112	}
113
114	/*
115	 * Having determined if privilege is restricted by various policies,
116	 * now determine if privilege is granted.  At this point, any policy
117	 * may grant privilege.  For now, we allow short-circuit boolean
118	 * evaluation, so may not call all policies.  Perhaps we should.
119	 *
120	 * Superuser policy grants privilege based on the effective (or in
121	 * the case of specific privileges, real) uid being 0.  We allow the
122	 * superuser policy to be globally disabled, although this is
123	 * currenty of limited utility.
124	 */
125	if (suser_enabled) {
126		switch (priv) {
127		case PRIV_MAXFILES:
128		case PRIV_MAXPROC:
129		case PRIV_PROC_LIMIT:
130			if (cred->cr_ruid == 0) {
131				error = 0;
132				goto out;
133			}
134			break;
135		default:
136			if (cred->cr_uid == 0) {
137				error = 0;
138				goto out;
139			}
140			break;
141		}
142	}
143
144	/*
145	 * Writes to kernel memory are a typical root-only operation,
146	 * but non-root users are expected to be able to read it.
147	 */
148	if (priv == PRIV_KMEM_READ) {
149		error = 0;
150		goto out;
151	}
152
153	/*
154	 * Now check with MAC, if enabled, to see if a policy module grants
155	 * privilege.
156	 */
157#ifdef MAC
158	if (mac_priv_grant(cred, priv) == 0) {
159		error = 0;
160		goto out;
161	}
162#endif
163
164	/*
165	 * The default is deny, so if no policies have granted it, reject
166	 * with a privilege error here.
167	 */
168	error = EPERM;
169out:
170	if (error)
171		SDT_PROBE1(priv, kernel, priv_check, priv_err, priv);
172	else
173		SDT_PROBE1(priv, kernel, priv_check, priv_ok, priv);
174	return (error);
175}
176
177int
178priv_check(struct thread *td, int priv)
179{
180
181	KASSERT(td == curthread, ("priv_check: td != curthread"));
182
183	return (priv_check_cred(td->td_ucred, priv, 0));
184}
185