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mac — Mandatory Access Control
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 UNIX security
provisions such as file permissions and superuser checks.
Currently, the following MAC policy modules are shipped with FreeBSD:
Name Description Labeling Load time
mac_biba(4) Biba integrity policy yes boot only
mac_bsdextended(4) File system firewall no any time
mac_ifoff(4) Interface silencing no any time
mac_lomac(4) Low-Watermark MAC policy yes boot only
mac_mls(4) Confidentiality policy yes boot only
mac_none(4) Sample no-op policy no any time
mac_partition(4) Process partition policy yes any time
mac_portacl(4) Port bind(2) access control no any time
mac_seeotheruids(4) See-other-UIDs policy no any time
mac_test(4) MAC testing policy no any time
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 maclabel(7)
MAC Support for UFS2 File Systems
By default, file system enforcement of labeled MAC policies relies on a
single file system label (see 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 “multilabel” flag
must be enabled on the file system. To set the “multilabel” flag, drop
to single-user mode and unmount the file system, then execute the
tunefs -l enable filesystem
where filesystem is either the mount point (in fstab(5)) or the special
file (in /dev) corresponding to the file system on which to enable
Policy enforcement is divided into the following areas of the system:
File system mounts, modifying directories, modifying files, etc.
Loading, unloading, and retrieving statistics on loaded kernel modules
Network interfaces, bpf(4), packet delivery and transmission, interface
configuration (ioctl(2), ifconfig(8))
Creation of and operation on pipe(2) objects
Debugging (e.g. ktrace(2)), process visibility (ps(1)), process execution
(execve(2)), signalling (kill(2))
Creation of and operation on socket(2) objects
Kernel environment (kenv(1)), system accounting (acct(2)), reboot(2),
settimeofday(2), swapon(2), sysctl(3), nfsd(8)-related operations
Setting MAC Labels
From the command line, each type of system object has its own means for
setting and modifying its MAC policy label.
File system object setfmac(8), setfsmac(8)
Network interface ifconfig(8)
TTY (by login class) login.conf(5)
User (by login class) login.conf(5)
Additionally, the su(1) and setpmac(8) utilities can be used to run a
command with a different process label than the shell's current label.
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
errno(2) returns from various system calls.
The interface for retrieving, handling, and setting policy labels is
documented in the mac(3) man page.
mac(3), mac_biba(4), mac_bsdextended(4), mac_ifoff(4), mac_lomac(4),
mac_mls(4), mac_none(4), mac_partition(4), mac_portacl(4),
mac_seeotheruids(4), mac_test(4), login.conf(5), maclabel(7), getfmac(8),
getpmac(8), setfmac(8), setpmac(8), mac(9)
"Mandatory Access Control", The FreeBSD Handbook,
The mac implementation first appeared in FreeBSD 5.0 and was developed by
the TrustedBSD Project.
This software was contributed to the FreeBSD Project by 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.
See mac(9) concerning appropriateness for production use. The TrustedBSD
MAC Framework is considered experimental in FreeBSD.
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.