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 <sys/cdefs.h>
32__FBSDID("$FreeBSD: releng/11.0/sys/kern/kern_priv.c 267992 2014-06-28 03:56:17Z hselasky $");
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/sdt.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_RWTUN,
57    &suser_enabled, 0, "processes with uid 0 have privilege");
58
59static int	unprivileged_mlock = 1;
60SYSCTL_INT(_security_bsd, OID_AUTO, unprivileged_mlock, CTLFLAG_RWTUN,
61    &unprivileged_mlock, 0, "Allow non-root users to call mlock(2)");
62
63SDT_PROVIDER_DEFINE(priv);
64SDT_PROBE_DEFINE1(priv, kernel, priv_check, priv__ok, "int");
65SDT_PROBE_DEFINE1(priv, kernel, priv_check, priv__err, "int");
66
67/*
68 * Check a credential for privilege.  Lots of good reasons to deny privilege;
69 * only a few to grant it.
70 */
71int
72priv_check_cred(struct ucred *cred, int priv, int flags)
73{
74	int error;
75
76	KASSERT(PRIV_VALID(priv), ("priv_check_cred: invalid privilege %d",
77	    priv));
78
79	/*
80	 * We first evaluate policies that may deny the granting of
81	 * privilege unilaterally.
82	 */
83#ifdef MAC
84	error = mac_priv_check(cred, priv);
85	if (error)
86		goto out;
87#endif
88
89	/*
90	 * Jail policy will restrict certain privileges that may otherwise be
91	 * be granted.
92	 */
93	error = prison_priv_check(cred, priv);
94	if (error)
95		goto out;
96
97	if (unprivileged_mlock) {
98		/*
99		 * Allow unprivileged users to call mlock(2)/munlock(2) and
100		 * mlockall(2)/munlockall(2).
101		 */
102		switch (priv) {
103		case PRIV_VM_MLOCK:
104		case PRIV_VM_MUNLOCK:
105			error = 0;
106			goto out;
107		}
108	}
109
110	/*
111	 * Having determined if privilege is restricted by various policies,
112	 * now determine if privilege is granted.  At this point, any policy
113	 * may grant privilege.  For now, we allow short-circuit boolean
114	 * evaluation, so may not call all policies.  Perhaps we should.
115	 *
116	 * Superuser policy grants privilege based on the effective (or in
117	 * the case of specific privileges, real) uid being 0.  We allow the
118	 * superuser policy to be globally disabled, although this is
119	 * currenty of limited utility.
120	 */
121	if (suser_enabled) {
122		switch (priv) {
123		case PRIV_MAXFILES:
124		case PRIV_MAXPROC:
125		case PRIV_PROC_LIMIT:
126			if (cred->cr_ruid == 0) {
127				error = 0;
128				goto out;
129			}
130			break;
131		default:
132			if (cred->cr_uid == 0) {
133				error = 0;
134				goto out;
135			}
136			break;
137		}
138	}
139
140	/*
141	 * Writes to kernel/physical memory are a typical root-only operation,
142	 * but non-root users are expected to be able to read it (provided they
143	 * have permission to access /dev/[k]mem).
144	 */
145	if (priv == PRIV_KMEM_READ) {
146		error = 0;
147		goto out;
148	}
149
150	/*
151	 * Now check with MAC, if enabled, to see if a policy module grants
152	 * privilege.
153	 */
154#ifdef MAC
155	if (mac_priv_grant(cred, priv) == 0) {
156		error = 0;
157		goto out;
158	}
159#endif
160
161	/*
162	 * The default is deny, so if no policies have granted it, reject
163	 * with a privilege error here.
164	 */
165	error = EPERM;
166out:
167	if (error)
168		SDT_PROBE1(priv, kernel, priv_check, priv__err, priv);
169	else
170		SDT_PROBE1(priv, kernel, priv_check, priv__ok, priv);
171	return (error);
172}
173
174int
175priv_check(struct thread *td, int priv)
176{
177
178	KASSERT(td == curthread, ("priv_check: td != curthread"));
179
180	return (priv_check_cred(td->td_ucred, priv, 0));
181}
182