.\" Copyright (c) 2002 Networks Associates Technology, Inc.
.\" All rights reserved.
.\"
.\" This software was developed for the FreeBSD Project by Chris Costello
.\" at Safeport Network Services and Network Associates Laboratories, 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.
.\"
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.Dd February 25, 2012
.Dt MAC_LOMAC 4
.Os
.Sh NAME
.Nm mac_lomac
.Nd "Low-watermark Mandatory Access Control data integrity policy"
.Sh SYNOPSIS
To compile LOMAC into your kernel, place the following lines in your kernel
configuration file:
.Bd -ragged -offset indent
.Cd "options MAC"
.Cd "options MAC_LOMAC"
.Ed
.Pp
Alternately, to load the LOMAC module at boot time, place the following line
in your kernel configuration file:
.Bd -ragged -offset indent
.Cd "options MAC"
.Ed
.Pp
and in
.Xr loader.conf 5 :
.Bd -literal -offset indent
mac_lomac_load="YES"
.Ed
.Sh DESCRIPTION
The
.Nm
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.
.Pp
Three special label component values exist:
.Bl -column -offset indent ".Sy Label" "dominated by all other labels"
.It Sy Label Ta Sy Comparison
.It Li low Ta "dominated by all other labels"
.It Li equal Ta "equal to all other labels"
.It Li high Ta "dominates all other labels"
.El
.Pp
The
.Dq Li high
label is assigned to system objects which affect the integrity of the system
as a whole.
The
.Dq Li equal
label
may be used to indicate that a particular subject or object is exempt from
the LOMAC protections.
For example, a label of
.Dq Li lomac/equal(equal-equal)
might be used on a subject which is to be used to administratively relabel
anything on the system.
.Pp
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:
.Pp
.Sm off
.D1 Li lomac / Ar grade Bq Ar auxgrade
.Sm on
.Pp
For example:
.Bd -literal -offset indent
lomac/10[2]
lomac/low
.Ed
.Pp
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:
.Pp
.Sm off
.D1 Li lomac / Ar singlegrade ( lograde No - Ar higrade )
.Sm on
.Pp
Modification of objects is restricted to access via the following comparison:
.Pp
.D1 Ar subject Ns :: Ns Ar higrade No \[>=] Ar target-object Ns :: Ns Ar grade
.Pp
Modification of subjects is the same, as the target subject's single grade
is the only element taken into comparison.
.Pp
Demotion of a subject occurs when the following comparison is true:
.Pp
.D1 Ar subject Ns :: Ns Ar singlegrade No > Ar object Ns :: Ns Ar grade
.Pp
When demotion occurs, the subject's
.Ar singlegrade
and
.Ar higrade
are reduced to the
object's grade, as well as the
.Ar lograde
if necessary.
When the demotion occurs, in addition to the permission of the subject being
reduced, shared
.Xr mmap 2
objects which it has opened in its memory space may be revoked according to
the following
.Xr sysctl 3
variables:
.Pp
.Bl -bullet -compact
.It
.Va security.mac.lomac.revocation_enabled
.It
.Va security.mac.enforce_vm
.It
.Va security.mac.mmap_revocation
.It
.Va security.mac.mmap_revocation_via_cow
.El
.Pp
Upon execution of a file, if the executable has an auxiliary label, and that
label is within the current range of
.Ar lograde Ns - Ns Ar 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.
.Pp
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.
.Pp
The LOMAC security model is quite similar to that of
.Xr mac_biba 4
and
.Xr mac_mls 4
in various ways.
More background information on this can be found in their respective
man pages.
.Sh SEE ALSO
.Xr mmap 2 ,
.Xr sysctl 3 ,
.Xr mac 4 ,
.Xr mac_biba 4 ,
.Xr mac_bsdextended 4 ,
.Xr mac_ifoff 4 ,
.Xr mac_mls 4 ,
.Xr mac_none 4 ,
.Xr mac_partition 4 ,
.Xr mac_portacl 4 ,
.Xr mac_seeotheruids 4 ,
.Xr mac_test 4 ,
.Xr mac 9
.Sh HISTORY
The
.Nm
policy module first appeared in
.Fx 5.0
and was developed by the
.Tn TrustedBSD
Project.
.Sh AUTHORS
This software was contributed to the
.Fx
Project by Network Associates Labs,
the Security Research Division of Network Associates
Inc.
under DARPA/SPAWAR contract N66001-01-C-8035
.Pq Dq CBOSS ,
as part of the DARPA CHATS research program.