287d467c5d
Generally, access to the kernel debugger is considered to be unsafe from a security perspective since it presents an unrestricted interface to inspect or modify the system state, including sensitive data such as signing keys. However, having some access to debugger functionality on production systems may be useful in determining the cause of a panic or hang. Therefore, it is desirable to have an optional policy which allows limited use of ddb(4) while disabling the functionality which could reveal system secrets. This loadable MAC module allows for the use of some ddb(4) commands while preventing the execution of others. The commands have been broadly grouped into three categories: - Those which are 'safe' and will not emit sensitive data (e.g. trace). Generally, these commands are deterministic and don't accept arguments. - Those which are definitively unsafe (e.g. examine <addr>, search <addr> <value>) - Commands which may be safe to execute depending on the arguments provided (e.g. show thread <addr>). Safe commands have been flagged as such with the DB_CMD_MEMSAFE flag. Commands requiring extra validation can provide a function to do so. For example, 'show thread <addr>' can be used as long as addr can be checked against the system's list of process structures. The policy also prevents debugger backends other than ddb(4) from executing, for example gdb(4). Reviewed by: markj, pauamma_gundo.com (manpages) Sponsored by: Juniper Networks, Inc. Sponsored by: Klara, Inc. Differential Revision: https://reviews.freebsd.org/D35371
249 lines
7.9 KiB
Groff
249 lines
7.9 KiB
Groff
.\" Copyright (c) 2003 Networks Associates Technology, Inc.
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.\" All rights reserved.
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.\"
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.\" This software was developed for the FreeBSD Project by Chris Costello
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.\" at Safeport Network Services and Network Associates Labs, the
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.\" Security Research Division of Network Associates, Inc. under
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.\" DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the
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.\" DARPA CHATS research program.
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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 AUTHORS 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 AUTHORS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd June 29, 2022
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.Dt MAC 4
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.Os
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.Sh NAME
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.Nm mac
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.Nd Mandatory Access Control
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.Sh SYNOPSIS
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.Cd "options MAC"
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.Sh DESCRIPTION
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.Ss Introduction
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The Mandatory Access Control, or MAC, framework allows administrators to
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finely control system security by providing for a loadable security policy
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architecture.
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It is important to note that due to its nature, MAC security policies may
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only restrict access relative to one another and the base system policy;
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they cannot override traditional
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.Ux
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security provisions such as file permissions and superuser checks.
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.Pp
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Currently, the following MAC policy modules are shipped with
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.Fx :
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.Bl -column ".Xr mac_seeotheruids 4" "ddb(4) interface restrictions" ".Em Labeling" "boot only"
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.It Sy Name Ta Sy Description Ta Sy Labeling Ta Sy "Load time"
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.It Xr mac_biba 4 Ta "Biba integrity policy" Ta yes Ta boot only
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.It Xr mac_bsdextended 4 Ta "File system firewall" Ta no Ta any time
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.It Xr mac_ddb 4 Ta "ddb(4) interface restrictions" Ta no Ta any time
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.It Xr mac_ifoff 4 Ta "Interface silencing" Ta no Ta any time
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.It Xr mac_lomac 4 Ta "Low-Watermark MAC policy" Ta yes Ta boot only
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.It Xr mac_mls 4 Ta "Confidentiality policy" Ta yes Ta boot only
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.It Xr mac_none 4 Ta "Sample no-op policy" Ta no Ta any time
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.It Xr mac_partition 4 Ta "Process partition policy" Ta yes Ta any time
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.It Xr mac_portacl 4 Ta "Port bind(2) access control" Ta no Ta any time
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.It Xr mac_seeotheruids 4 Ta "See-other-UIDs policy" Ta no Ta any time
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.It Xr mac_test 4 Ta "MAC testing policy" Ta no Ta any time
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.El
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.Ss MAC Labels
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Each system subject (processes, sockets, etc.) and each system object
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(file system objects, sockets, etc.) can carry with it a MAC label.
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MAC labels contain data in an arbitrary format
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taken into consideration in making access control decisions
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for a given operation.
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Most MAC labels on system subjects and objects
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can be modified directly or indirectly by the system
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administrator.
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The format for a given policy's label may vary depending on the type
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of object or subject being labeled.
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More information on the format for MAC labels can be found in the
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.Xr maclabel 7
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man page.
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.Ss MAC Support for UFS2 File Systems
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By default, file system enforcement of labeled MAC policies relies on
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a single file system label
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(see
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.Sx "MAC Labels" )
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in order to make access control decisions for all the files in a particular
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file system.
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With some policies, this configuration may not allow administrators to take
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full advantage of features.
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In order to enable support for labeling files on an individual basis
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for a particular file system,
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the
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.Dq multilabel
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flag must be enabled on the file system.
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To set the
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.Dq multilabel
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flag, drop to single-user mode and unmount the file system,
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then execute the following command:
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.Pp
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.Dl "tunefs -l enable" Ar filesystem
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.Pp
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where
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.Ar filesystem
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is either the mount point
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(in
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.Xr fstab 5 )
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or the special file
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(in
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.Pa /dev )
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corresponding to the file system on which to enable multilabel support.
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.Ss Policy Enforcement
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Policy enforcement is divided into the following areas of the system:
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.Bl -ohang
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.It Sy "File System"
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File system mounts, modifying directories, modifying files, etc.
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.It Sy KLD
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Loading, unloading, and retrieving statistics on loaded kernel modules
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.It Sy Network
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Network interfaces,
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.Xr bpf 4 ,
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packet delivery and transmission,
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interface configuration
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.Xr ( ioctl 2 ,
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.Xr ifconfig 8 )
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.It Sy Pipes
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Creation of and operation on
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.Xr pipe 2
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objects
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.It Sy Processes
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Debugging
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(e.g.\&
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.Xr ktrace 2 ) ,
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process visibility
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.Pq Xr ps 1 ,
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process execution
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.Pq Xr execve 2 ,
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signalling
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.Pq Xr kill 2
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.It Sy Sockets
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Creation of and operation on
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.Xr socket 2
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objects
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.It Sy System
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Kernel environment
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.Pq Xr kenv 1 ,
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system accounting
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.Pq Xr acct 2 ,
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.Xr reboot 2 ,
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.Xr settimeofday 2 ,
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.Xr swapon 2 ,
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.Xr sysctl 3 ,
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.Xr nfsd 8 Ns
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-related operations
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.It Sy VM
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.Xr mmap 2 Ns
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-ed files
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.El
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.Ss Setting MAC Labels
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From the command line, each type of system object has its own means for setting
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and modifying its MAC policy label.
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.Bl -column "user (by login class)" "Xr setfmac 8 , Xr setfsmac 8" -offset indent
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.It Sy "Subject/Object" Ta Sy "Utility"
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.It "File system object" Ta Xr setfmac 8 , Xr setfsmac 8
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.It "Network interface" Ta Xr ifconfig 8
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.It "TTY (by login class)" Ta Xr login.conf 5
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.It "User (by login class)" Ta Xr login.conf 5
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.El
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.Pp
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Additionally, the
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.Xr su 1
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and
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.Xr setpmac 8
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utilities can be used to run a command with a different process label than
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the shell's current label.
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.Ss Programming With MAC
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MAC security enforcement itself is transparent to application
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programs, with the exception that some programs may need to be aware of
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additional
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.Xr errno 2
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returns from various system calls.
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.Pp
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The interface for retrieving, handling, and setting policy labels
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is documented in the
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.Xr mac 3
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man page.
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.\" *** XXX ***
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.\" Support for this feature is poor and should not be encouraged.
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.\"
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.\" .It Va security.mac.mmap_revocation
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.\" Revoke
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.\" .Xr mmap 2
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.\" access to files on subject relabel.
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.\" .It Va security.mac.mmap_revocation_via_cow
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.\" Revoke
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.\" .Xr mmap 2
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.\" access to files via copy-on-write semantics;
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.\" mapped regions will still appear writable, but will no longer
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.\" effect a change on the underlying vnode.
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.\" (Default: 0).
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.Sh SEE ALSO
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.Xr mac 3 ,
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.Xr mac_biba 4 ,
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.Xr mac_bsdextended 4 ,
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.Xr mac_ddb 4 ,
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.Xr mac_ifoff 4 ,
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.Xr mac_lomac 4 ,
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.Xr mac_mls 4 ,
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.Xr mac_none 4 ,
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.Xr mac_partition 4 ,
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.Xr mac_portacl 4 ,
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.Xr mac_seeotheruids 4 ,
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.Xr mac_test 4 ,
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.Xr login.conf 5 ,
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.Xr maclabel 7 ,
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.Xr getfmac 8 ,
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.Xr getpmac 8 ,
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.Xr setfmac 8 ,
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.Xr setpmac 8 ,
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.Xr mac 9
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.Rs
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.%B "The FreeBSD Handbook"
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.%T "Mandatory Access Control"
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.%U https://docs.FreeBSD.org/en/books/handbook/mac/
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.Re
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.Sh HISTORY
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The
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.Nm
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implementation first appeared in
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.Fx 5.0
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and was developed by the
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.Tn TrustedBSD
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Project.
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.Sh AUTHORS
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This software was contributed to the
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.Fx
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Project by Network Associates Labs,
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the Security Research Division of Network Associates
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Inc.
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under DARPA/SPAWAR contract N66001-01-C-8035
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.Pq Dq CBOSS ,
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as part of the DARPA CHATS research program.
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.Sh BUGS
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While the MAC Framework design is intended to support the containment of
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the root user, not all attack channels are currently protected by entry
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point checks.
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As such, MAC Framework policies should not be relied on, in isolation,
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to protect against a malicious privileged user.
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