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MAC_LOMAC(4)		 BSD Kernel Interfaces Manual		  MAC_LOMAC(4)

NAME
     mac_lomac — Low-watermark Mandatory Access Control data integrity policy

SYNOPSIS
     To compile LOMAC into your kernel, place the following lines in your ker‐
     nel configuration file:

	   options MAC
	   options MAC_LOMAC

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

	   options MAC

     and in loader.conf(5):

	   mac_lomac_load="YES"

DESCRIPTION
     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:

	   Label    Comparison
	   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:

	   lomac/grade[auxgrade]

     For example:

	   lomac/10[2]
	   lomac/low

     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:

	   lomac/singlegrade(lograde-higrade)

     Modification of objects is restricted to access via the following compar‐
     ison:

	   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:

     ·	 security.mac.lomac.revocation_enabled
     ·	 security.mac.enforce_vm
     ·	 security.mac.mmap_revocation
     ·	 security.mac.mmap_revocation_via_cow

     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 ALSO
     mmap(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.

AUTHORS
     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
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