199 lines
7.1 KiB
Groff
199 lines
7.1 KiB
Groff
.\" Copyright (c) 2002 Networks Associates Technology, Inc.
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.\" All rights reserved.
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.\"
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.\" This software was developed for the FreeBSD Project by Chris Costello
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.\" at Safeport Network Services and Network Associates Laboratories, the
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.\" Security Research Division of Network Associates, Inc. under
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.\" DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the
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.\" DARPA CHATS research program.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.Dd December 11, 2002
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.Os
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.Dt MAC_LOMAC 4
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.Sh NAME
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.Nm mac_lomac
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.Nd Low-watermark Mandatory Access Control data integrity policy
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.Sh SYNOPSIS
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To compile LOMAC into your kernel, place the following lines in your kernel
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configuration file:
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.Cd "options MAC"
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.Cd "options MAC_LOMAC"
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.Pp
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Alternately, to load the LOMAC module at boot time, place the following line
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in your kernel configuration file:
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.Cd "options MAC"
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.Pp
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and in
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.Xr loader.conf 5 :
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.Cd mac_lomac_load= Ns \&"YES"
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.Sh DESCRIPTION
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The
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.Nm
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policy module implements the LOMAC integrity model,
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which protects the integrity of system objects and subjects by means of
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an information flow policy coupled with the subject demotion
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via floating labels.
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In LOMAC, all system subjects and objects are assigned integrity labels, made
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up of one or more hierarchal grades, depending on the their types.
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Together, these label elements permit all labels to be placed in a partial
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order, with information flow protections and demotion decisions
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based on a dominance operator
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describing the order.
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The hierarchal grade field or fields are expressed
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as a value between 0 and 65535,
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with higher values reflecting higher integrity.
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.Pp
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Three special label component values exist:
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.Bl -column -offset indent ".Sy Label" "dominated by all other labels"
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.It Sy Label Ta Sy Comparison
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.It Li low Ta dominated by all other labels
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.It Li equal Ta equal to all other labels
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.It Li high Ta dominates all other labels
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.El
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.Pp
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The
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.Dq high
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label is assigned to system objects which affect the integrity of the system
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as a whole.
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.Dq equal
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may be used to indicate that a particular subject or object is exempt from
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the LOMAC protections.
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For example, a label of
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.Dq lomac/equal(equal-equal)
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might be used on a subject which is to be used to administratively relabel
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anything on the system.
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.Pp
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Almost all system objects are tagged with a single, active label element,
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reflecting the integrity of the object, or integrity of the data contained
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in the object.
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Filesystem objects may contain an additional auxiliary label which
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determines the inherited integrity level for new files created in a
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directory or the alternate label assumed by the subject upon execution of
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an executable.
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In general, objects labels are represented in the following form:
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.Pp
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.Dl lomac/ Ns Sy grade Ns [ Sy auxgrade ]
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.Pp
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For example:
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.Pp
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.Bd -literal -offset indent
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lomac/10[2]
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lomac/low
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.Ed
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.Pp
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Subject labels consist of three label elements: a single (active) label,
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as well as a range of available labels.
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This range is represented using two ordered LOMAC label elements, and when set
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on a process, permits the process to change its active label to any label of
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greater or equal integrity to the low end of the range, and lesser or equal
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integrity to the high end of the range.
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In general, subject labels are represented in the following form:
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.Pp
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.Dl lomac/ Ns Sy singlegrade Ns ( Sy lograde Ns - Ns Sy higrade )
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.Pp
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Modification of objects is restricted to access via the following comparison:
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.Pp
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.Dl subject::higrade >= target-object::grade
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.Pp
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Modification of subjects is the same, as the target subject's single grade
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is the only element taken into comparison.
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.Pp
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Demotion of a subject occurs when the following comparison is true:
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.Pp
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.Dl subject::singlegrade > object::grade
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.Pp
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When demotion occurs, the subject's singlegrade and higrade are reduced to the
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object's grade, as well as the lograde if necessary.
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When the demotion occurs, in addition to the permission of the subject being
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reduced, shared
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.Xr mmap 2
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objects which it has opened in its memory space may be revoked according to
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the following
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.Xr sysctl 2
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variables:
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.Bl -bullet
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.It
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.Va security.mac.lomac.revocation_enabled
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.It
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.Va security.mac.enforce_vm
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.It
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.Va security.mac.mmap_revocation
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.It
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.Va security.mac.mmap_revocation_via_cow
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.El
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.Pp
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Upon execution of a file, if the executable has an auxiliary label, and that
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label is within the current range of
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.Sy lograde-higrade ,
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it will be assumed by the subject immediately.
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After this, demotion is performed just as with any other read operation, with
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the executable as the target.
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Through the use of auxiliary labels, programs may be initially executed
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at a lower effective integrity level,
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while retaining the ability to raise it again.
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.Pp
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These rules prevent subjects of lower integrity from influencing the
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behavior of higher integrity subjects by preventing the flow of information,
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and hence control, from allowing low integrity subjects to modify either
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a high integrity object or high integrity subjects acting on those objects.
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LOMAC integrity policies may be appropriate in a number of environments,
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both from the perspective of preventing corruption of the operating system,
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and corruption of user data if marked as higher integrity than the attacker.
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.Pp
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The LOMAC security model is quite similar to that of
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.Xr mac_biba 4
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and
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.Xr mac_mls 4
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in various ways.
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More background information on this can be found in their respective
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man pages.
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.Sh SEE ALSO
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.Xr mmap 2 ,
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.Xr sysctl 2 ,
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.Xr mac 4 ,
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.Xr mac_biba 4 ,
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.Xr mac_bsdextended 4 ,
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.Xr mac_ifoff 4 ,
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.Xr mac_mls 4 ,
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.Xr mac_none 4 ,
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.Xr mac_partition 4 ,
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.Xr mac_portacl 4 ,
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.Xr mac_seeotheruids 4 ,
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.Xr mac_test 4 ,
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.Xr mac 9
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.Sh HISTORY
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The
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.Nm
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policy module first appeared in
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.Fx 5.0
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and was developed by the TrustedBSD Project.
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.Sh AUTHORS
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This software was contributed to the
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.Fx
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Project by Network Associates Labs,
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the Security Research Division of Network Associates
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Inc. under DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"),
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as part of the DARPA CHATS research program.
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