214 lines
6.0 KiB
C
214 lines
6.0 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 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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/*
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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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/*
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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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#ifdef MAC
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error = mac_priv_check(cred, priv);
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if (error)
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goto out;
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#endif
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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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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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/*
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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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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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