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.

Debian                                          February 25, 2012                                   MAC_LOMAC(4)