This commit adds the priv(9) that waters down the sysctl to make it only allow read(2) of a dirfd by the system root. Jailed root is not allowed, but jail policy and superuser policy will abstain from allowing/denying it so that a MAC module can fully control the policy. Such a MAC module has been written, and can be found at: https://people.freebsd.org/~kevans/mac_read_dir-0.1.0.tar.gz It is expected that the MAC module won't be needed by many, as most only need to do such diagnostics that require this behavior as system root anyways. Interested parties are welcome to grab the MAC module above and create a port or locally integrate it, and with enough support it could see introduction to base. As noted in mac_read_dir.c, it is released under the BSD 2 clause license and allows the restrictions to be lifted for only jailed root or for all unprivileged users. PR: 246412 Reviewed by: mckusick, kib, emaste, jilles, cy, phk, imp (all previous) Reviewed by: rgrimes (latest version) Differential Revision: https://reviews.freebsd.org/D24596
274 lines
7.2 KiB
C
274 lines
7.2 KiB
C
/*-
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* SPDX-License-Identifier: BSD-2-Clause-FreeBSD
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*
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* Copyright (c) 2006 nCircle Network Security, Inc.
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* Copyright (c) 2009 Robert N. M. Watson
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* All rights reserved.
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*
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* This software was developed by Robert N. M. Watson for the TrustedBSD
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* Project under contract to nCircle Network Security, Inc.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR, NCIRCLE NETWORK SECURITY,
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* INC., OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
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* TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
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* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
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* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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#include <sys/param.h>
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#include <sys/jail.h>
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#include <sys/kernel.h>
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#include <sys/priv.h>
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#include <sys/proc.h>
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#include <sys/sdt.h>
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#include <sys/sysctl.h>
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#include <sys/systm.h>
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#include <security/mac/mac_framework.h>
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/*
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* `suser_enabled' (which can be set by the security.bsd.suser_enabled
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* sysctl) determines whether the system 'super-user' policy is in effect. If
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* it is nonzero, an effective uid of 0 connotes special privilege,
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* overriding many mandatory and discretionary protections. If it is zero,
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* uid 0 is offered no special privilege in the kernel security policy.
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* Setting it to zero may seriously impact the functionality of many existing
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* userland programs, and should not be done without careful consideration of
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* the consequences.
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*/
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static int __read_mostly suser_enabled = 1;
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SYSCTL_INT(_security_bsd, OID_AUTO, suser_enabled, CTLFLAG_RWTUN,
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&suser_enabled, 0, "processes with uid 0 have privilege");
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static int unprivileged_mlock = 1;
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SYSCTL_INT(_security_bsd, OID_AUTO, unprivileged_mlock, CTLFLAG_RWTUN,
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&unprivileged_mlock, 0, "Allow non-root users to call mlock(2)");
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static int unprivileged_read_msgbuf = 1;
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SYSCTL_INT(_security_bsd, OID_AUTO, unprivileged_read_msgbuf,
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CTLFLAG_RW, &unprivileged_read_msgbuf, 0,
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"Unprivileged processes may read the kernel message buffer");
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SDT_PROVIDER_DEFINE(priv);
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SDT_PROBE_DEFINE1(priv, kernel, priv_check, priv__ok, "int");
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SDT_PROBE_DEFINE1(priv, kernel, priv_check, priv__err, "int");
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static __always_inline int
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priv_check_cred_pre(struct ucred *cred, int priv)
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{
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int error;
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#ifdef MAC
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error = mac_priv_check(cred, priv);
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#else
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error = 0;
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#endif
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return (error);
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}
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static __always_inline int
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priv_check_cred_post(struct ucred *cred, int priv, int error, bool handled)
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{
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if (__predict_true(handled))
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goto out;
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/*
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* Now check with MAC, if enabled, to see if a policy module grants
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* privilege.
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*/
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#ifdef MAC
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if (mac_priv_grant(cred, priv) == 0) {
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error = 0;
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goto out;
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}
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#endif
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/*
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* The default is deny, so if no policies have granted it, reject
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* with a privilege error here.
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*/
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error = EPERM;
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out:
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if (SDT_PROBES_ENABLED()) {
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if (error)
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SDT_PROBE1(priv, kernel, priv_check, priv__err, priv);
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else
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SDT_PROBE1(priv, kernel, priv_check, priv__ok, priv);
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}
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return (error);
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}
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/*
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* Check a credential for privilege. Lots of good reasons to deny privilege;
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* only a few to grant it.
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*/
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int
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priv_check_cred(struct ucred *cred, int priv)
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{
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int error;
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KASSERT(PRIV_VALID(priv), ("priv_check_cred: invalid privilege %d",
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priv));
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switch (priv) {
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case PRIV_VFS_GENERATION:
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return (priv_check_cred_vfs_generation(cred));
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}
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/*
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* We first evaluate policies that may deny the granting of
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* privilege unilaterally.
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*/
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error = priv_check_cred_pre(cred, priv);
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if (error)
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goto out;
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/*
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* Jail policy will restrict certain privileges that may otherwise be
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* be granted.
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*/
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error = prison_priv_check(cred, priv);
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if (error)
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goto out;
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if (unprivileged_mlock) {
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/*
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* Allow unprivileged users to call mlock(2)/munlock(2) and
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* mlockall(2)/munlockall(2).
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*/
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switch (priv) {
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case PRIV_VM_MLOCK:
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case PRIV_VM_MUNLOCK:
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error = 0;
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goto out;
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}
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}
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if (unprivileged_read_msgbuf) {
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/*
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* Allow an unprivileged user to read the kernel message
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* buffer.
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*/
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if (priv == PRIV_MSGBUF) {
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error = 0;
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goto out;
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}
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}
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/*
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* Having determined if privilege is restricted by various policies,
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* now determine if privilege is granted. At this point, any policy
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* may grant privilege. For now, we allow short-circuit boolean
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* evaluation, so may not call all policies. Perhaps we should.
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*
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* Superuser policy grants privilege based on the effective (or in
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* the case of specific privileges, real) uid being 0. We allow the
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* superuser policy to be globally disabled, although this is
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* currenty of limited utility.
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*/
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if (suser_enabled) {
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switch (priv) {
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case PRIV_MAXFILES:
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case PRIV_MAXPROC:
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case PRIV_PROC_LIMIT:
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if (cred->cr_ruid == 0) {
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error = 0;
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goto out;
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}
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break;
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case PRIV_VFS_READ_DIR:
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/*
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* Allow PRIV_VFS_READ_DIR for root if we're not in a
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* jail, otherwise deny unless a MAC policy grants it.
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*/
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if (jailed(cred))
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break;
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/* FALLTHROUGH */
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default:
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if (cred->cr_uid == 0) {
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error = 0;
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goto out;
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}
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break;
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}
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}
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/*
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* Writes to kernel/physical memory are a typical root-only operation,
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* but non-root users are expected to be able to read it (provided they
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* have permission to access /dev/[k]mem).
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*/
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if (priv == PRIV_KMEM_READ) {
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error = 0;
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goto out;
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}
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/*
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* Allow unprivileged process debugging on a per-jail basis.
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* Do this here instead of prison_priv_check(), so it can also
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* apply to prison0.
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*/
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if (priv == PRIV_DEBUG_UNPRIV) {
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if (prison_allow(cred, PR_ALLOW_UNPRIV_DEBUG)) {
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error = 0;
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goto out;
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}
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}
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return (priv_check_cred_post(cred, priv, error, false));
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out:
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return (priv_check_cred_post(cred, priv, error, true));
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}
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int
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priv_check(struct thread *td, int priv)
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{
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KASSERT(td == curthread, ("priv_check: td != curthread"));
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return (priv_check_cred(td->td_ucred, priv));
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}
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int
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priv_check_cred_vfs_generation(struct ucred *cred)
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{
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int error;
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error = priv_check_cred_pre(cred, PRIV_VFS_GENERATION);
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if (error)
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goto out;
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if (jailed(cred)) {
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error = EPERM;
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goto out;
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}
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if (cred->cr_uid == 0 && suser_enabled) {
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error = 0;
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goto out;
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}
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return (priv_check_cred_post(cred, PRIV_VFS_GENERATION, error, false));
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out:
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return (priv_check_cred_post(cred, PRIV_VFS_GENERATION, error, true));
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}
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