MAC_LOMAC(4) BSD Kernel Interfaces Manual MAC_LOMAC(4)NAMEmac_lomac — Low-watermark Mandatory Access Control data integrity policy
To compile LOMAC into your kernel, place the following lines in your ker‐
nel configuration file:
Alternately, to load the LOMAC module at boot time, place the following
line in your kernel configuration file:
and in loader.conf(5):
The mac_lomac policy module implements the LOMAC integrity model, which
protects the integrity of system objects and subjects by means of an
information flow policy coupled with the subject demotion via floating
labels. In LOMAC, all system subjects and objects are assigned integrity
labels, made up of one or more hierarchal grades, depending on the their
types. Together, these label elements permit all labels to be placed in
a partial order, with information flow protections and demotion decisions
based on a dominance operator describing the order. The hierarchal grade
field or fields are expressed as a value between 0 and 65535, with higher
values reflecting higher integrity.
Three special label component values exist:
low dominated by all other labels
equal equal to all other labels
high dominates all other labels
The “high” label is assigned to system objects which affect the integrity
of the system as a whole. The “equal” label may be used to indicate that
a particular subject or object is exempt from the LOMAC protections. For
example, a label of “lomac/equal(equal-equal)” might be used on a subject
which is to be used to administratively relabel anything on the system.
Almost all system objects are tagged with a single, active label element,
reflecting the integrity of the object, or integrity of the data con‐
tained in the object. File system objects may contain an additional aux‐
iliary label which determines the inherited integrity level for new files
created in a directory or the alternate label assumed by the subject upon
execution of an executable. In general, objects labels are represented
in the following form:
Subject labels consist of three label elements: a single (active) label,
as well as a range of available labels. This range is represented using
two ordered LOMAC label elements, and when set on a process, permits the
process to change its active label to any label of greater or equal
integrity to the low end of the range, and lesser or equal integrity to
the high end of the range. In general, subject labels are represented in
the following form:
Modification of objects is restricted to access via the following compar‐
subject::higrade ≥ target-object::grade
Modification of subjects is the same, as the target subject's single
grade is the only element taken into comparison.
Demotion of a subject occurs when the following comparison is true:
subject::singlegrade > object::grade
When demotion occurs, the subject's singlegrade and higrade are reduced
to the object's grade, as well as the lograde if necessary. When the
demotion occurs, in addition to the permission of the subject being
reduced, shared mmap(2) objects which it has opened in its memory space
may be revoked according to the following sysctl(3) variables:
Upon execution of a file, if the executable has an auxiliary label, and
that label is within the current range of lograde-higrade, it will be
assumed by the subject immediately. After this, demotion is performed
just as with any other read operation, with the executable as the target.
Through the use of auxiliary labels, programs may be initially executed
at a lower effective integrity level, while retaining the ability to
raise it again.
These rules prevent subjects of lower integrity from influencing the
behavior of higher integrity subjects by preventing the flow of informa‐
tion, and hence control, from allowing low integrity subjects to modify
either a high integrity object or high integrity subjects acting on those
objects. LOMAC integrity policies may be appropriate in a number of
environments, both from the perspective of preventing corruption of the
operating system, and corruption of user data if marked as higher
integrity than the attacker.
The LOMAC security model is quite similar to that of mac_biba(4) and
mac_mls(4) in various ways. More background information on this can be
found in their respective man pages.
SEE ALSOmmap(2), sysctl(3), mac(4), mac_biba(4), mac_bsdextended(4),
mac_ifoff(4), mac_mls(4), mac_none(4), mac_partition(4), mac_portacl(4),
mac_seeotheruids(4), mac_test(4), mac(9)HISTORY
The mac_lomac policy module first appeared in FreeBSD 5.0 and was devel‐
oped by the TrustedBSD Project.
This software was contributed to the FreeBSD Project by Network Asso‐
ciates 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.
BSD December 11, 2002 BSD