253 lines
8.7 KiB
Groff
253 lines
8.7 KiB
Groff
.\" Copyright (c) 2002-2004 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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.\"
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.Dd December 1, 2002
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.Os
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.Dt MAC_MLS 4
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.Sh NAME
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.Nm mac_mls
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.Nd "Multi-Level Security confidentiality policy"
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.Sh SYNOPSIS
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To compile MLS into your kernel, place the following lines in your kernel
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configuration file:
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.Bd -ragged -offset indent
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.Cd "options MAC"
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.Cd "options MAC_MLS"
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.Ed
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.Pp
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Alternately, to load the MLS module at boot time, place the following line
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in your kernel configuration file:
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.Bd -ragged -offset indent
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.Cd "options MAC"
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.Ed
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.Pp
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and in
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.Xr loader.conf 5 :
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.Bd -literal -offset indent
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mac_mls_load="YES"
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.Ed
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.Sh DESCRIPTION
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The
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.Nm
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policy module implements the Multi-Level Security, or MLS model,
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which controls access between subjects and objects based on their
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confidentiality by means of a strict information flow policy.
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Each subject and object in the system has an MLS label associated with it;
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each subject's MLS label contains information on its clearance level,
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and each object's MLS label contains information on its classification.
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.Pp
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In MLS, all system subjects and objects are assigned confidentiality labels,
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made up of a sensitivity level and zero or more compartments.
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Together, these label elements permit all labels to be placed in a partial
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order, with confidentiality protections based on a dominance operator
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describing the order.
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The sensitivity level is expressed as a value between 0 and
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65535, with higher values reflecting higher sensitivity levels.
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The compartment field is expressed as a set of up to 256 components,
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numbered from 1 to 256.
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A complete label consists of both sensitivity and compartment
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elements.
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.Pp
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With normal labels, dominance is defined as a label having a higher
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or equal active sensitivity level, and having at least
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all of the same compartments as the label to which it is being compared.
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With respect to label comparisons,
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.Dq Li lower
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is defined as being dominated by the label to which it is being compared,
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and
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.Dq Li higher
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is defined as dominating the label to which it is being compared,
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and
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.Dq Li equal
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is defined as both labels being able to satisfy the dominance requirements
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over one another.
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.Pp
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Three special label values exist:
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.Bl -column -offset indent ".Li mls/equal" "dominated by all other labels"
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.It Sy Label Ta Sy Comparison
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.It Li mls/low Ta "dominated by all other labels"
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.It Li mls/equal Ta "equal to all other labels"
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.It Li mls/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 Li mls/equal
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label may be applied to subjects and objects for which no enforcement of the
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MLS security policy is desired.
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.Pp
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The MLS model enforces the following basic restrictions:
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.Bl -bullet
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.It
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Subjects may not observe the processes of another subject if its
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clearance level is lower than the clearance level of the object it is
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attempting to observe.
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.It
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Subjects may not read, write, or otherwise observe objects without proper
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clearance (e.g.\& subjects may not observe objects whose classification label
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dominates its own clearance label)
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.It
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Subjects may not write to objects with a lower classification level than
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its own clearance level.
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.It
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A subject may read and write to an object if its clearance level is equal
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to the object's classification level as though MLS protections were not in
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place.
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.El
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.Pp
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These rules prevent subjects of lower clearance from gaining access
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information classified beyond its clearance level in order to protect the
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confidentiality of classified information, subjects of higher clearance
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from writing to objects of lower classification in order to prevent the
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accidental or malicious leaking of information, and subjects of lower
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clearance from observing subjects of higher clearance altogether.
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In traditional trusted operating systems, the MLS confidentiality model is
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used in concert with the Biba integrity model
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.Xr ( mac_biba 4 )
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in order to protect the Trusted Code Base (TCB).
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.Ss Label Format
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Almost all system objects are tagged with an effective, active label element,
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reflecting the classification of the object, or classification of the data
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contained in the object.
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In general, object labels are represented in the following form:
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.Pp
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.Sm off
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.D1 Li mls / Ar grade : compartments
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.Sm on
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.Pp
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For example:
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.Bd -literal -offset indent
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mls/10:2+3+6
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mls/low
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.Ed
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.Pp
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Subject labels consist of three label elements: an effective (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 MLS 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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.Sm off
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.D1 Li mls / Ar effectivegrade : effectivecompartments ( lograde : locompartments No -
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.D1 Ar higrade : hicompartments )
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.Sm on
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.Pp
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For example:
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.Bd -literal -offset indent
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mls/10:2+3+6(5:2+3-20:2+3+4+5+6)
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mls/high(low-high)
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.Ed
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.Pp
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Valid ranged labels must meet the following requirement regarding their
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elements:
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.Pp
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.D1 Ar rangehigh No \[>=] Ar effective No \[>=] Ar rangelow
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.Pp
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One class of objects with ranges currently exists, the network interface.
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In the case of the network interface, the effective label element references
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the default label for packets received over the interface, and the range
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represents the range of acceptable labels of packets to be transmitted over
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the interface.
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.Ss Runtime Configuration
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The following
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.Xr sysctl 8
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MIBs are available for fine-tuning the enforcement of this MAC policy.
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.Bl -tag -width ".Va security.mac.mls.ptys_equal"
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.It Va security.mac.mls.enabled
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Enables the enforcement of the MLS confidentiality policy.
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(Default: 1).
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.It Va security.mac.mls.ptys_equal
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Label
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.Xr pty 4 Ns s
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as
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.Dq Li mls/equal
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upon creation.
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(Default: 0).
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.It Va security.mac.mls.revocation_enabled
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Revoke access to objects if the label is changed to a more sensitive
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level than the subject.
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(Default: 0).
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.El
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.Sh IMPLEMENTATION NOTES
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Currently, the
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.Nm
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policy relies on superuser status
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.Pq Xr suser 9
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in order to change network interface MLS labels.
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This will eventually go away, but it is currently a liability and may
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allow the superuser to bypass MLS protections.
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.Sh SEE ALSO
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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_lomac 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 maclabel 7 ,
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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
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.Tn TrustedBSD
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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 Laboratories,
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the Security Research Division of Network Associates
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Inc.\& under DARPA/SPAWAR contract N66001-01-C-8035
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.Pq Dq CBOSS ,
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as part of the DARPA CHATS research program.
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.Sh BUGS
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See
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.Xr mac 9
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concerning appropriateness for production use.
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The
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.Tn TrustedBSD
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MAC Framework is considered experimental in
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.Fx .
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.Pp
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While the MAC Framework design is intended to support the containment of
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the root user, not all attack channels are currently protected by entry
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point checks.
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As such, MAC Framework policies should not be relied on, in isolation,
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to protect against a malicious privileged user.
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