/*-
* SPDX-License-Identifier: BSD-2-Clause-FreeBSD
*
* Copyright (c) 2006 nCircle Network Security, Inc.
* Copyright (c) 2009 Robert N. M. Watson
* Copyright (c) 2020 Mariusz Zaborski <oshogbo@FreeBSD.org>
* All rights reserved.
*
* This software was developed by Robert N. M. Watson for the TrustedBSD
* Project under contract to nCircle Network Security, Inc.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR, NCIRCLE NETWORK SECURITY,
* INC., OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
* TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include <sys/param.h>
#include <sys/jail.h>
#include <sys/kernel.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/sx.h>
#include <sys/priv.h>
#include <sys/proc.h>
#include <sys/sdt.h>
#include <sys/sysctl.h>
#include <sys/systm.h>
#include <security/mac/mac_framework.h>
/*
* `suser_enabled' (which can be set by the security.bsd.suser_enabled
* sysctl) determines whether the system 'super-user' policy is in effect. If
* it is nonzero, an effective uid of 0 connotes special privilege,
* overriding many mandatory and discretionary protections. If it is zero,
* uid 0 is offered no special privilege in the kernel security policy.
* Setting it to zero may seriously impact the functionality of many existing
* userland programs, and should not be done without careful consideration of
* the consequences.
*/
static bool
suser_enabled(struct ucred *cred)
{
return (prison_allow(cred, PR_ALLOW_SUSER));
}
static int
sysctl_kern_suser_enabled(SYSCTL_HANDLER_ARGS)
{
struct ucred *cred;
int error, enabled;
cred = req->td->td_ucred;
enabled = suser_enabled(cred);
error = sysctl_handle_int(oidp, &enabled, 0, req);
if (error || !req->newptr)
return (error);
prison_set_allow(cred, PR_ALLOW_SUSER, enabled);
return (0);
}
SYSCTL_PROC(_security_bsd, OID_AUTO, suser_enabled, CTLTYPE_INT |
CTLFLAG_RWTUN | CTLFLAG_PRISON | CTLFLAG_MPSAFE, 0, 0,
&sysctl_kern_suser_enabled, "I", "Processes with uid 0 have privilege");
static int unprivileged_mlock = 1;
SYSCTL_INT(_security_bsd, OID_AUTO, unprivileged_mlock, CTLFLAG_RWTUN,
&unprivileged_mlock, 0, "Allow non-root users to call mlock(2)");
static int unprivileged_read_msgbuf = 1;
SYSCTL_INT(_security_bsd, OID_AUTO, unprivileged_read_msgbuf,
CTLFLAG_RW, &unprivileged_read_msgbuf, 0,
"Unprivileged processes may read the kernel message buffer");
SDT_PROVIDER_DEFINE(priv);
SDT_PROBE_DEFINE1(priv, kernel, priv_check, priv__ok, "int");
SDT_PROBE_DEFINE1(priv, kernel, priv_check, priv__err, "int");
static __always_inline int
priv_check_cred_pre(struct ucred *cred, int priv)
{
int error;
#ifdef MAC
error = mac_priv_check(cred, priv);
#else
error = 0;
#endif
return (error);
}
static __always_inline int
priv_check_cred_post(struct ucred *cred, int priv, int error, bool handled)
{
if (__predict_true(handled))
goto out;
/*
* Now check with MAC, if enabled, to see if a policy module grants
* privilege.
*/
#ifdef MAC
if (mac_priv_grant(cred, priv) == 0) {
error = 0;
goto out;
}
#endif
/*
* The default is deny, so if no policies have granted it, reject
* with a privilege error here.
*/
error = EPERM;
out:
if (SDT_PROBES_ENABLED()) {
if (error)
SDT_PROBE1(priv, kernel, priv_check, priv__err, priv);
else
SDT_PROBE1(priv, kernel, priv_check, priv__ok, priv);
}
return (error);
}
/*
* Check a credential for privilege. Lots of good reasons to deny privilege;
* only a few to grant it.
*/
int
priv_check_cred(struct ucred *cred, int priv)
{
int error;
KASSERT(PRIV_VALID(priv), ("priv_check_cred: invalid privilege %d",
priv));
switch (priv) {
case PRIV_VFS_LOOKUP:
return (priv_check_cred_vfs_lookup(cred));
case PRIV_VFS_GENERATION:
return (priv_check_cred_vfs_generation(cred));
}
/*
* We first evaluate policies that may deny the granting of
* privilege unilaterally.
*/
error = priv_check_cred_pre(cred, priv);
if (error)
goto out;
/*
* Jail policy will restrict certain privileges that may otherwise be
* be granted.
*/
error = prison_priv_check(cred, priv);
if (error)
goto out;
if (unprivileged_mlock) {
/*
* Allow unprivileged users to call mlock(2)/munlock(2) and
* mlockall(2)/munlockall(2).
*/
switch (priv) {
case PRIV_VM_MLOCK:
case PRIV_VM_MUNLOCK:
error = 0;
goto out;
}
}
if (unprivileged_read_msgbuf) {
/*
* Allow an unprivileged user to read the kernel message
* buffer.
*/
if (priv == PRIV_MSGBUF) {
error = 0;
goto out;
}
}
/*
* Having determined if privilege is restricted by various policies,
* now determine if privilege is granted. At this point, any policy
* may grant privilege. For now, we allow short-circuit boolean
* evaluation, so may not call all policies. Perhaps we should.
*
* Superuser policy grants privilege based on the effective (or in
* the case of specific privileges, real) uid being 0. We allow the
* superuser policy to be globally disabled, although this is
* currenty of limited utility.
*/
if (suser_enabled(cred)) {
switch (priv) {
case PRIV_MAXFILES:
case PRIV_MAXPROC:
case PRIV_PROC_LIMIT:
if (cred->cr_ruid == 0) {
error = 0;
goto out;
}
break;
case PRIV_VFS_READ_DIR:
/*
* Allow PRIV_VFS_READ_DIR for root if we're not in a
* jail, otherwise deny unless a MAC policy grants it.
*/
if (jailed(cred))
break;
/* FALLTHROUGH */
default:
if (cred->cr_uid == 0) {
error = 0;
goto out;
}
break;
}
}
/*
* Writes to kernel/physical memory are a typical root-only operation,
* but non-root users are expected to be able to read it (provided they
* have permission to access /dev/[k]mem).
*/
if (priv == PRIV_KMEM_READ) {
error = 0;
goto out;
}
/*
* Allow unprivileged process debugging on a per-jail basis.
* Do this here instead of prison_priv_check(), so it can also
* apply to prison0.
*/
if (priv == PRIV_DEBUG_UNPRIV) {
if (prison_allow(cred, PR_ALLOW_UNPRIV_DEBUG)) {
error = 0;
goto out;
}
}
return (priv_check_cred_post(cred, priv, error, false));
out:
return (priv_check_cred_post(cred, priv, error, true));
}
int
priv_check(struct thread *td, int priv)
{
KASSERT(td == curthread, ("priv_check: td != curthread"));
return (priv_check_cred(td->td_ucred, priv));
}
static int __noinline
priv_check_cred_vfs_lookup_slow(struct ucred *cred)
{
int error;
error = priv_check_cred_pre(cred, PRIV_VFS_LOOKUP);
if (error)
goto out;
if (cred->cr_uid == 0 && suser_enabled(cred)) {
error = 0;
goto out;
}
return (priv_check_cred_post(cred, PRIV_VFS_LOOKUP, error, false));
out:
return (priv_check_cred_post(cred, PRIV_VFS_LOOKUP, error, true));
}
int
priv_check_cred_vfs_lookup(struct ucred *cred)
{
int error;
if (__predict_false(mac_priv_check_fp_flag ||
mac_priv_grant_fp_flag || SDT_PROBES_ENABLED()))
return (priv_check_cred_vfs_lookup_slow(cred));
error = EPERM;
if (cred->cr_uid == 0 && suser_enabled(cred))
error = 0;
return (error);
}
int
priv_check_cred_vfs_lookup_nomac(struct ucred *cred)
{
int error;
if (__predict_false(mac_priv_check_fp_flag ||
mac_priv_grant_fp_flag || SDT_PROBES_ENABLED()))
return (EAGAIN);
error = EPERM;
if (cred->cr_uid == 0 && suser_enabled(cred))
error = 0;
return (error);
}
static int __noinline
priv_check_cred_vfs_generation_slow(struct ucred *cred)
{
int error;
error = priv_check_cred_pre(cred, PRIV_VFS_GENERATION);
if (error)
goto out;
if (jailed(cred)) {
error = EPERM;
goto out;
}
if (cred->cr_uid == 0 && suser_enabled(cred)) {
error = 0;
goto out;
}
return (priv_check_cred_post(cred, PRIV_VFS_GENERATION, error, false));
out:
return (priv_check_cred_post(cred, PRIV_VFS_GENERATION, error, true));
}
int
priv_check_cred_vfs_generation(struct ucred *cred)
{
int error;
if (__predict_false(mac_priv_check_fp_flag ||
mac_priv_grant_fp_flag || SDT_PROBES_ENABLED()))
return (priv_check_cred_vfs_generation_slow(cred));
error = EPERM;
if (!jailed(cred) && cred->cr_uid == 0 && suser_enabled(cred))
error = 0;
return (error);
}
