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MAC_BSDEXTENDED(4) FreeBSD Kernel Interfaces Manual MAC_BSDEXTENDED(4)

file system firewall policy

To compile the file system firewall policy into your kernel, place the following lines in your kernel configuration file:
options MAC

Alternately, to load the file system firewall policy module at boot time, place the following line in your kernel configuration file:

options MAC

and in loader.conf(5):


The mac_bsdextended security policy module provides an interface for the system administrator to impose mandatory rules regarding users and some system objects. Rules are uploaded to the module (typically using ugidfw(8), or some other tool utilizing libugidfw(3)) where they are stored internally and used to determine whether to allow or deny specific accesses (see ugidfw(8)).

While the traditional mac(9) entry points are implemented, policy labels are not used; instead, access control decisions are made by iterating through the internal list of rules until a rule which denies the particular access is found, or the end of the list is reached. The mac_bsdextended policy works similar to ipfw(8) or by using a first match semantic. This means that not all rules are applied, only the first matched rule; thus if Rule A allows access and Rule B blocks access, Rule B will never be applied.

The following sysctls may be used to tweak the behavior of mac_bsdextended:
Set to zero or one to toggle the policy off or on.
List the number of defined rules, the maximum rule count is current set at 256.
List the number of rule slots currently being used.
Toggle between the old all rules match functionality and the new first rule matches functionality. This is enabled by default.
Log all access violations via the AUTHPRIV syslog(3) facility.
Currently does nothing interesting.

libugidfw(3), syslog(3), mac(4), mac_biba(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), ipfw(8), ugidfw(8), mac(9)

The mac_bsdextended policy module first appeared in FreeBSD 5.0 and was developed by the TrustedBSD Project.

The "match first case" and logging capabilities were later added by Tom Rhodes <>.

This software was contributed to the FreeBSD Project by NAI 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.
May 21, 2005 FreeBSD 13.1-RELEASE

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