bd230b9731
to no longer claim they are experimental. Reviewed by: rwatson@, wblock@ MFC after: 1 week Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D2985
244 lines
8.6 KiB
Groff
244 lines
8.6 KiB
Groff
.\" Copyright (c) 2002-2004 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.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND
|
|
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE
|
|
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
|
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
|
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
|
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
|
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
|
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
.\" SUCH DAMAGE.
|
|
.\"
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd July 25, 2015
|
|
.Dt MAC_MLS 4
|
|
.Os
|
|
.Sh NAME
|
|
.Nm mac_mls
|
|
.Nd "Multi-Level Security confidentiality policy"
|
|
.Sh SYNOPSIS
|
|
To compile MLS into your kernel, place the following lines in your kernel
|
|
configuration file:
|
|
.Bd -ragged -offset indent
|
|
.Cd "options MAC"
|
|
.Cd "options MAC_MLS"
|
|
.Ed
|
|
.Pp
|
|
Alternately, to load the MLS 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_mls_load="YES"
|
|
.Ed
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Nm
|
|
policy module implements the Multi-Level Security, or MLS model,
|
|
which controls access between subjects and objects based on their
|
|
confidentiality by means of a strict information flow policy.
|
|
Each subject and object in the system has an MLS label associated with it;
|
|
each subject's MLS label contains information on its clearance level,
|
|
and each object's MLS label contains information on its classification.
|
|
.Pp
|
|
In MLS, all system subjects and objects are assigned confidentiality labels,
|
|
made up of a sensitivity level and zero or more compartments.
|
|
Together, these label elements permit all labels to be placed in a partial
|
|
order, with confidentiality protections based on a dominance operator
|
|
describing the order.
|
|
The sensitivity level is expressed as a value between 0 and
|
|
65535, with higher values reflecting higher sensitivity levels.
|
|
The compartment field is expressed as a set of up to 256 components,
|
|
numbered from 1 to 256.
|
|
A complete label consists of both sensitivity and compartment
|
|
elements.
|
|
.Pp
|
|
With normal labels, dominance is defined as a label having a higher
|
|
or equal active sensitivity level, and having at least
|
|
all of the same compartments as the label to which it is being compared.
|
|
With respect to label comparisons,
|
|
.Dq Li lower
|
|
is defined as being dominated by the label to which it is being compared,
|
|
and
|
|
.Dq Li higher
|
|
is defined as dominating the label to which it is being compared,
|
|
and
|
|
.Dq Li equal
|
|
is defined as both labels being able to satisfy the dominance requirements
|
|
over one another.
|
|
.Pp
|
|
Three special label values exist:
|
|
.Bl -column -offset indent ".Li mls/equal" "dominated by all other labels"
|
|
.It Sy Label Ta Sy Comparison
|
|
.It Li mls/low Ta "dominated by all other labels"
|
|
.It Li mls/equal Ta "equal to all other labels"
|
|
.It Li mls/high Ta "dominates all other labels"
|
|
.El
|
|
.Pp
|
|
The
|
|
.Dq Li mls/equal
|
|
label may be applied to subjects and objects for which no enforcement of the
|
|
MLS security policy is desired.
|
|
.Pp
|
|
The MLS model enforces the following basic restrictions:
|
|
.Bl -bullet
|
|
.It
|
|
Subjects may not observe the processes of another subject if its
|
|
clearance level is lower than the clearance level of the object it is
|
|
attempting to observe.
|
|
.It
|
|
Subjects may not read, write, or otherwise observe objects without proper
|
|
clearance (e.g.\& subjects may not observe objects whose classification label
|
|
dominates its own clearance label)
|
|
.It
|
|
Subjects may not write to objects with a lower classification level than
|
|
its own clearance level.
|
|
.It
|
|
A subject may read and write to an object if its clearance level is equal
|
|
to the object's classification level as though MLS protections were not in
|
|
place.
|
|
.El
|
|
.Pp
|
|
These rules prevent subjects of lower clearance from gaining access
|
|
information classified beyond its clearance level in order to protect the
|
|
confidentiality of classified information, subjects of higher clearance
|
|
from writing to objects of lower classification in order to prevent the
|
|
accidental or malicious leaking of information, and subjects of lower
|
|
clearance from observing subjects of higher clearance altogether.
|
|
In traditional trusted operating systems, the MLS confidentiality model is
|
|
used in concert with the Biba integrity model
|
|
.Xr ( mac_biba 4 )
|
|
in order to protect the Trusted Code Base (TCB).
|
|
.Ss Label Format
|
|
Almost all system objects are tagged with an effective, active label element,
|
|
reflecting the classification of the object, or classification of the data
|
|
contained in the object.
|
|
In general, object labels are represented in the following form:
|
|
.Pp
|
|
.Sm off
|
|
.D1 Li mls / Ar grade : compartments
|
|
.Sm on
|
|
.Pp
|
|
For example:
|
|
.Bd -literal -offset indent
|
|
mls/10:2+3+6
|
|
mls/low
|
|
.Ed
|
|
.Pp
|
|
Subject labels consist of three label elements: an effective (active) label,
|
|
as well as a range of available labels.
|
|
This range is represented using two ordered MLS 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 mls / Ar effectivegrade : effectivecompartments ( lograde : locompartments No -
|
|
.D1 Ar higrade : hicompartments )
|
|
.Sm on
|
|
.Pp
|
|
For example:
|
|
.Bd -literal -offset indent
|
|
mls/10:2+3+6(5:2+3-20:2+3+4+5+6)
|
|
mls/high(low-high)
|
|
.Ed
|
|
.Pp
|
|
Valid ranged labels must meet the following requirement regarding their
|
|
elements:
|
|
.Pp
|
|
.D1 Ar rangehigh No \[>=] Ar effective No \[>=] Ar rangelow
|
|
.Pp
|
|
One class of objects with ranges currently exists, the network interface.
|
|
In the case of the network interface, the effective label element references
|
|
the default label for packets received over the interface, and the range
|
|
represents the range of acceptable labels of packets to be transmitted over
|
|
the interface.
|
|
.Ss Runtime Configuration
|
|
The following
|
|
.Xr sysctl 8
|
|
MIBs are available for fine-tuning the enforcement of this MAC policy.
|
|
.Bl -tag -width ".Va security.mac.mls.ptys_equal"
|
|
.It Va security.mac.mls.enabled
|
|
Enables the enforcement of the MLS confidentiality policy.
|
|
(Default: 1).
|
|
.It Va security.mac.mls.ptys_equal
|
|
Label
|
|
.Xr pty 4 Ns s
|
|
as
|
|
.Dq Li mls/equal
|
|
upon creation.
|
|
(Default: 0).
|
|
.It Va security.mac.mls.revocation_enabled
|
|
Revoke access to objects if the label is changed to a more sensitive
|
|
level than the subject.
|
|
(Default: 0).
|
|
.El
|
|
.Sh IMPLEMENTATION NOTES
|
|
Currently, the
|
|
.Nm
|
|
policy relies on superuser status
|
|
.Pq Xr suser 9
|
|
in order to change network interface MLS labels.
|
|
This will eventually go away, but it is currently a liability and may
|
|
allow the superuser to bypass MLS protections.
|
|
.Sh SEE ALSO
|
|
.Xr mac 4 ,
|
|
.Xr mac_biba 4 ,
|
|
.Xr mac_bsdextended 4 ,
|
|
.Xr mac_ifoff 4 ,
|
|
.Xr mac_lomac 4 ,
|
|
.Xr mac_none 4 ,
|
|
.Xr mac_partition 4 ,
|
|
.Xr mac_portacl 4 ,
|
|
.Xr mac_seeotheruids 4 ,
|
|
.Xr mac_test 4 ,
|
|
.Xr maclabel 7 ,
|
|
.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 Laboratories,
|
|
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.
|
|
.Sh BUGS
|
|
While the MAC Framework design is intended to support the containment of
|
|
the root user, not all attack channels are currently protected by entry
|
|
point checks.
|
|
As such, MAC Framework policies should not be relied on, in isolation,
|
|
to protect against a malicious privileged user.
|