NAME

     mac_lomac — Low-watermark Mandatory Access Control data integrity policy

SYNOPSIS

     To compile LOMAC into your kernel, place the following lines in your kernel 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 hierarchical grades, depending on 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 contained in the object.  File system
     objects may contain an additional auxiliary 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 comparison:

           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 information, 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 developed by the
     TrustedBSD Project.

AUTHORS

     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.