man/man4/mac.4

.\" Copyright (c) 2003 Networks Associates Technology, Inc.
.\" All rights reserved.
.\"
.\" This software was developed for the FreeBSD Project by Chris Costello
.\" at Safeport Network Services and Network Associates Labs, the
.\" Security Research Division of Network Associates, Inc. under
.\" DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the
.\" DARPA CHATS research program.
.\"
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.\" modification, are permitted provided that the following conditions
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.\"    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
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND
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.\" $FreeBSD$
.\"
.Dd May 20, 2021
.Dt MAC 4
.Os
.Sh NAME
.Nm mac
.Nd Mandatory Access Control
.Sh SYNOPSIS
.Cd "options MAC"
.Sh DESCRIPTION
.Ss Introduction
The Mandatory Access Control, or MAC, framework allows administrators to
finely control system security by providing for a loadable security policy
architecture.
It is important to note that due to its nature, MAC security policies may
only restrict access relative to one another and the base system policy;
they cannot override traditional
.Ux
security provisions such as file permissions and superuser checks.
.Pp
Currently, the following MAC policy modules are shipped with
.Fx :
.Bl -column ".Xr mac_seeotheruids 4" "low-watermark mac policy" ".Em Labeling" "boot only"
.It Sy Name Ta Sy Description Ta Sy Labeling Ta Sy "Load time"
.It Xr mac_biba 4 Ta "Biba integrity policy" Ta yes Ta boot only
.It Xr mac_bsdextended 4 Ta "File system firewall" Ta no Ta any time
.It Xr mac_ifoff 4 Ta "Interface silencing" Ta no Ta any time
.It Xr mac_lomac 4 Ta "Low-Watermark MAC policy" Ta yes Ta boot only
.It Xr mac_mls 4 Ta "Confidentiality policy" Ta yes Ta boot only
.It Xr mac_none 4 Ta "Sample no-op policy" Ta no Ta any time
.It Xr mac_partition 4 Ta "Process partition policy" Ta yes Ta any time
.It Xr mac_portacl 4 Ta "Port bind(2) access control" Ta no Ta any time
.It Xr mac_seeotheruids 4 Ta "See-other-UIDs policy" Ta no Ta any time
.It Xr mac_test 4 Ta "MAC testing policy" Ta no Ta any time
.El
.Ss MAC Labels
Each system subject (processes, sockets, etc.) and each system object
(file system objects, sockets, etc.) can carry with it a MAC label.
MAC labels contain data in an arbitrary format
taken into consideration in making access control decisions
for a given operation.
Most MAC labels on system subjects and objects
can be modified directly or indirectly by the system
administrator.
The format for a given policy's label may vary depending on the type
of object or subject being labeled.
More information on the format for MAC labels can be found in the
.Xr maclabel 7
man page.
.Ss MAC Support for UFS2 File Systems
By default, file system enforcement of labeled MAC policies relies on
a single file system label
(see
.Sx "MAC Labels" )
in order to make access control decisions for all the files in a particular
file system.
With some policies, this configuration may not allow administrators to take
full advantage of features.
In order to enable support for labeling files on an individual basis
for a particular file system,
the
.Dq multilabel
flag must be enabled on the file system.
To set the
.Dq multilabel
flag, drop to single-user mode and unmount the file system,
then execute the following command:
.Pp
.Dl "tunefs -l enable" Ar filesystem
.Pp
where
.Ar filesystem
is either the mount point
(in
.Xr fstab 5 )
or the special file
(in
.Pa /dev )
corresponding to the file system on which to enable multilabel support.
.Ss Policy Enforcement
Policy enforcement is divided into the following areas of the system:
.Bl -ohang
.It Sy "File System"
File system mounts, modifying directories, modifying files, etc.
.It Sy KLD
Loading, unloading, and retrieving statistics on loaded kernel modules
.It Sy Network
Network interfaces,
.Xr bpf 4 ,
packet delivery and transmission,
interface configuration
.Xr ( ioctl 2 ,
.Xr ifconfig 8 )
.It Sy Pipes
Creation of and operation on
.Xr pipe 2
objects
.It Sy Processes
Debugging
(e.g.\&
.Xr ktrace 2 ) ,
process visibility
.Pq Xr ps 1 ,
process execution
.Pq Xr execve 2 ,
signalling
.Pq Xr kill 2
.It Sy Sockets
Creation of and operation on
.Xr socket 2
objects
.It Sy System
Kernel environment
.Pq Xr kenv 1 ,
system accounting
.Pq Xr acct 2 ,
.Xr reboot 2 ,
.Xr settimeofday 2 ,
.Xr swapon 2 ,
.Xr sysctl 3 ,
.Xr nfsd 8 Ns
-related operations
.It Sy VM
.Xr mmap 2 Ns
-ed files
.El
.Ss Setting MAC Labels
From the command line, each type of system object has its own means for setting
and modifying its MAC policy label.
.Bl -column "user (by login class)" "Xr setfmac 8 , Xr setfsmac 8" -offset indent
.It Sy "Subject/Object" Ta Sy "Utility"
.It "File system object" Ta Xr setfmac 8 , Xr setfsmac 8
.It "Network interface" Ta Xr ifconfig 8
.It "TTY (by login class)" Ta Xr login.conf 5
.It "User (by login class)" Ta Xr login.conf 5
.El
.Pp
Additionally, the
.Xr su 1
and
.Xr setpmac 8
utilities can be used to run a command with a different process label than
the shell's current label.
.Ss Programming With MAC
MAC security enforcement itself is transparent to application
programs, with the exception that some programs may need to be aware of
additional
.Xr errno 2
returns from various system calls.
.Pp
The interface for retrieving, handling, and setting policy labels
is documented in the
.Xr mac 3
man page.
.\" *** XXX ***
.\" Support for this feature is poor and should not be encouraged.
.\"
.\" .It Va security.mac.mmap_revocation
.\" Revoke
.\" .Xr mmap 2
.\" access to files on subject relabel.
.\" .It Va security.mac.mmap_revocation_via_cow
.\" Revoke
.\" .Xr mmap 2
.\" access to files via copy-on-write semantics;
.\" mapped regions will still appear writable, but will no longer
.\" effect a change on the underlying vnode.
.\" (Default: 0).
.Sh SEE ALSO
.Xr mac 3 ,
.Xr mac_biba 4 ,
.Xr mac_bsdextended 4 ,
.Xr mac_ifoff 4 ,
.Xr mac_lomac 4 ,
.Xr mac_mls 4 ,
.Xr mac_none 4 ,
.Xr mac_partition 4 ,
.Xr mac_portacl 4 ,
.Xr mac_seeotheruids 4 ,
.Xr mac_test 4 ,
.Xr login.conf 5 ,
.Xr maclabel 7 ,
.Xr getfmac 8 ,
.Xr getpmac 8 ,
.Xr setfmac 8 ,
.Xr setpmac 8 ,
.Xr mac 9
.Rs
.%B "The FreeBSD Handbook"
.%T "Mandatory Access Control"
.%U https://docs.FreeBSD.org/en/books/handbook/mac/
.Re
.Sh HISTORY
The
.Nm
implementation first appeared in
.Fx 5.0
and was developed by the
.Tn TrustedBSD
Project.
.Sh AUTHORS
This software was contributed to the
.Fx
Project by Network Associates Labs,
the Security Research Division of Network Associates
Inc.
under DARPA/SPAWAR contract N66001-01-C-8035
.Pq Dq CBOSS ,
as part of the DARPA CHATS research program.
.Sh BUGS
While the MAC Framework design is intended to support the containment of
the root user, not all attack channels are currently protected by entry
point checks.
As such, MAC Framework policies should not be relied on, in isolation,
to protect against a malicious privileged user.