Internet Engineering Task Force (IETF) D. Quigley
Request for Comments: 7569
Category: Standards Track J. Lu
ISSN: 2070-1721 Oracle
T. Haynes
Primary Data
June 2015
Registry Specification for Mandatory Access Control (MAC)
Security Label Formats
Abstract
In the past, Mandatory Access Control (MAC) systems have used very
rigid policies that were implemented in particular protocols and
platforms. As MAC systems become more widely deployed, additional
flexibility in mechanism and policy will be required. While
traditional trusted systems implemented Multi-Level Security (MLS)
and integrity models, modern systems have expanded to include such
technologies as type enforcement. Due to the wide range of policies
and mechanisms that need to be accommodated, it is unlikely that the
use of a single security label format and model will be viable.
To allow multiple MAC mechanisms and label formats to co-exist in a
network, this document creates a registry of label format
specifications. This registry contains label format identifiers and
provides for the association of each such identifier with a
corresponding extensive document outlining the exact syntax and use
of the particular label format.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7569.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Existing Label Format Specifications . . . . . . . . . . . . 4
3.1. IP Security Option (IPSO), Basic Security Option (BSO) . 4
3.2. Commercial IP Security Option (CIPSO) . . . . . . . . . . 4
3.3. Common Architecture Label IPv6 Security Option (CALIPSO) 5
3.4. Flux Advanced Security Kernel (FLASK) . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
5.1. Initial Registry . . . . . . . . . . . . . . . . . . . . 6
5.2. Adding a New Entry to the Registry . . . . . . . . . . . 6
5.3. Obsoleting a Label Format Specifier . . . . . . . . . . . 7
5.4. Modifying an Existing Entry in the Registry . . . . . . . 8
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.1. Normative References . . . . . . . . . . . . . . . . . . 8
6.2. Informative References . . . . . . . . . . . . . . . . . 8
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
With the acceptance of security labels in several mainstream
operating systems, the need to communicate labels between these
systems becomes more important. In a typical client-and-server
scenario, the client request to the server acts as a subject trying
to access an object on the server [RFC7204]. Unfortunately, these
systems are diverse enough that attempts at establishing one common
label format have been unsuccessful. This is because systems
implement different Mandatory Access Control (MAC) models, which
typically do not share any common ground.
One solution might be to define a single label format that consists
of the union of the requirements of all MAC models/implementations,
known at a given time. This approach is not desirable, because it
introduces an environment where either (1) many MAC models would have
blank fields for many of the label's components or (2) many
implementations would ignore altogether many of the values that are
present. The resulting complexity would be likely to result in a
confusing situation in which the interaction of fields that are
derived from different MAC models is never clearly specified and the
addition of new models or extensions of existing models is unduly
difficult.
An additional consideration is that if a policy authority or
identifier field is specified in the label format, it would require a
robust description that would encompass multiple MAC models where an
implementation would lock policy administration into the described
model.
Ideally, a mechanism to address this problem should allow the most
flexibility possible in terms of policy administration while
providing a specification that is sufficient to allow for
implementation of the label format and understanding of the semantics
of the label. This means that the label format specification would
ideally contain a syntactic description of the label format and a
description of the semantics for each component in the label. This
allows protocols to specify the type of label and label semantics
that it requires while leaving policy and policy administration to
the individual organizations using the protocol in their environment.
Policy administration within an organization is a difficult problem.
This should not be made even more difficult by having to request
permission from external entities when crafting new policy or just
making department specific modifications to existing policies. The
policy authority field would allow a label format specification to
specify a scheme for policy administration without forcing it on all
users of security labels. However, by agreeing to implement a
particular label format specification, the protocol agrees to that
policy administration mechanism when processing labels of that type.
This document creates a registry of label format specifications to
allow multiple MAC mechanisms and label formats to co-exist in a
network. While the initial use of this registry is for the Network
File System (NFS) protocol, it might also be referenced and used by
other IETF protocols in the future.
2. Definitions
Label Format Specifier: an identifier used by the client to
establish the syntactic format of the security label and the
semantic meaning of its components.
Label Format Specification: a reference to a stable, public document
that specifies the label format.
Multi-Level Security (MLS): a traditional model where subjects are
given a security level (Unclassified, Secret, Top Secret, etc.)
and objects are given security labels that mandate the access of
the subject to the object (see [BL73], [RFC2401], [BL73] and [RFC4301]). [RFC2401]).
(Although RFC 2401 has been obsoleted by RFC 4301, RFC 2401 is
still the definitive reference for MLS as discussed in this
document.)
object: a passive resource within the system that we wish to
protect. Objects can be entities such as files, directories,
pipes, sockets, and many other system resources relevant to the
protection of the system state.
subject: an active entity, usually a process, user, or client, that
is requesting access to an object.
3. Existing Label Format Specifications
3.1. IP Security Option (IPSO), Basic Security Option (BSO)
The "IP Security Option (IPSO)" label format is defined in [RFC1108].
IANA has assigned IPv4 Option 130 to the IPSO Basic Security Option
(BSO). IPSO is the only IPv4 sensitivity label option implemented in
commercial IP routers. IPSO BSO continues to have widespread
implementation in hosts, and widespread deployment. For the purposes
of this document, only the BSO labels in Table 1 on Page 3 of
[RFC1108] are used.
In some locales, the BSO value "(Reserved 2)" is used for marking
information that is considered "Restricted" by local policy, where
"Restricted" is less sensitive than "Confidential" but more sensitive
than "Unclassified".
3.2. Commercial IP Security Option (CIPSO)
The "Commercial IP Security Option (CIPSO)" label format is
documented in [CIPSO] and in [FIPS-188]. While [CIPSO] is long
expired, it is widely supported in deployed MLS systems that support
IPv4. IANA has assigned IPv4 option number 134 to CIPSO. CIPSO is
defined ONLY as an IPv4 option. IANA has never assigned any IPv6
option value to CIPSO.
3.3. Common Architecture Label IPv6 Security Option (CALIPSO)
The "Common Architecture Label IPv6 Security Option (CALIPSO)" label
format is specified in [RFC5570] and is defined for IPv6. As noted
in Section 10 of [RFC5570], CALIPSO is a direct derivative of the
IPv4 "Son of IPSO" (SIPSO); therefore, CALIPSO is NOT derived from
CIPSO in any way.
3.4. Flux Advanced Security Kernel (FLASK)
The Flux Advanced Security Kernel (FLASK) [FLASK99] is an
implementation of an architecture to provide flexible support for
security policies. Section 2.1 of [FLASK99b] summarizes the
architecture of FLASK and describes:
1. the interactions between a subsystem that enforces security
policy decisions and a subsystem that makes those decisions.
2. the requirements on the components within each subsystem.
4. Security Considerations
This document defines a mechanism to associate the Label Format
Specifier identifier with a document outlining the syntax and format
of a label. There are no security considerations for such an
association. The label specification documents referenced by each
registration entry should state security considerations for the label
mechanism it specifies.
5. IANA Considerations
This section provides guidance to the Internet Assigned Numbers
Authority (IANA) regarding the creation of a new registry in
accordance with [RFC5226].
Per this document, IANA has created a new registry called "Security
Label Format Selection Registry". The new registry has the following
fields:
Label Format Specifier: An integer that maps to a particular label
format, e.g., the CALIPSO label format defined by [RFC5570]. The
namespace of this identifier has the range of 0..65535.
Label Description: A human-readable ASCII [RFC20] text string that
describes the label format, e.g., "Common Architecture Label IPv6
Security Option (CALIPSO)". The length of this field is limited
to 128 bytes.
Status: A short ASCII text string indicating the status of an entry
in the registry. The status field for most entries should have
the value "active". In the case where a label format selection
entry is obsolete, the status field of the obsoleted entry should
be "obsoleted by entry NNN".
Label Format Specification: A reference to a stable, public document
that specifies the label format, e.g., a URL to [RFC5570].
5.1. Initial Registry
The initial assignments of the registry are as follows:
+---------------+---------------------+--------+--------------------+
| Label Format | Description | Status | Reference |
| Specifier | | | |
+---------------+---------------------+--------+--------------------+
| 0 | Reserved | - | - |
| 1 - 127 | Private Use | - | - |
| 128 - 255 | Experimental Use | - | - |
| 256 | CIPSO (tag type #1) | active | [FIPS-188] |
| 257 | CALIPSO [RFC5570] | active | [RFC5570] |
| 258 | FLASK Security | active | [FLASK99] |
| | Context | | |
| 259 | IPSO | active | [RFC1108] |
| 260 - 65535 | Available for IANA | - | - |
| | Assignment | | |
+---------------+---------------------+--------+--------------------+
Label Format Specifier Ranges
Table 1
5.2. Adding a New Entry to the Registry
A label format specification document is required to add a new entry
to the "Security Label Format Selection Registry". If the label
format document is inside the RFC path, then the IANA Considerations
section of the label format document should clearly reference the
"Security Label Format Selection Registry" and request allocation of
a new entry. The well-known IANA policy Specification Required, as
defined in Section 4.1 of [RFC5226], will be used to handle such
requests. Note that the "Specification Required" policy implies that
this process requires a Designated Expert, i.e., adding a new entry
to this registry requires both a published label format specification
and a Designated Expert review.
In reviewing the published label format specification, the Designated
Expert should consider whether or not the specification provides
sufficient semantics for the object and subject labels to enforce the
MAC model and policy administration when deployed within an
organization. Another consideration is if the label format allows a
correct and complete implementation of the protocol to process and
enforce labels as a policy administration mechanism. Finally, to
reduce interoperability issues, the reviewer must determine if the
new label format specification has clearly defined syntax and
semantics for the proposed new labels.
5.3. Obsoleting a Label Format Specifier
In the case where a label format selector number is assigned to a
label format and the label format specification is changed later, a
new selector assignment should be requested. The same Specification
Required IANA policy applies to such requests. The IANA
Considerations section of the updated label format specification
should be explicit regarding which old label selector assignment it
obsoletes. Below is an example of an obsoleted entry in the
registry:
+--------------+--------------------+-----------+-------------------+
| Label Format | Description | Status | Reference |
| Specifier | | | |
+--------------+--------------------+-----------+-------------------+
| 0 | Reserved | - | - |
| 1 - 127 | Private Use | - | - |
| 128 - 255 | Experimental Use | - | - |
| 256 | CIPSO (tag type | active | [FIPS-188] |
| | #1) | | |
| 257 | CALIPSO [RFC5570] | active | [RFC5570] |
| 258 | FLASK Security | obsoleted | [FLASK99] |
| | Context | by 263 | |
| ... | | | |
| 263 | FLASK Security | active | [new spec URL] |
| | Context (v2) | | |
| 264 - 65535 | Available for IANA | - | - |
| | Assignment | | |
+--------------+--------------------+-----------+-------------------+
Example Label Format Specifier Updated Ranges
Table 2
5.4. Modifying an Existing Entry in the Registry
A request to modify either the Description or the published label
format specification will also require the Specification Required
IANA policy to be applied. The Designated Expert reviewer will need
to determine if the published label format specification either
obsoletes the Label Format Specifier or updates the label syntax and/
or model. If the Label Format Specifier is obsoleted, then the
reviewer will follow the process defined in Section 5.3. Otherwise,
for the update of the label syntax and/or the model, the reviewer
will approve the change.
6. References
6.1. Normative References
[RFC20] Cerf, V., "ASCII format for network interchange", STD 80,
RFC 20, DOI 10.17487/RFC0020, October 1969,
<http://www.rfc-editor.org/info/rfc20>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>.
6.2. Informative References
[BL73] Bell, D. and L. LaPadula, "Secure Computer Systems:
Mathematical Foundations and Model", Technical Report
M74-244, The MITRE Corporation, Bedford, MA, May 1973.
[CIPSO] IETF CIPSO Working Group, "Commercial IP Security Option
(CIPSO 2.2)", Work in Progress, draft-ietf-cipso-
ipsecurity-01, July 1992.
[FIPS-188]
US National Institute of Standards and Technology,
"Standard Security Labels for Information Transfer",
Federal Information Processing Standards (FIPS) 188,
September 1994,
<http://csrc.nist.gov/publications/fips/fips188/
fips188.pdf>.
[FLASK99] Spencer, R., Smalley, S., Loscocco, P., Hibler, M.,
Andersen, D., and J. Lepreau, "The Flask Security
Architecture: System Support for Diverse Security
Policies", In Proceedings of the Eighth USENIX Security
Symposium, pages 123-139, August 1999,
<https://www.cs.cmu.edu/~dga/papers/flask-
usenixsec99.pdf>.
[FLASK99b]
Secure Computing Corporation, "Assurance in the Fluke
Microkernel Formal Security Policy Model", Document
00-0930896A001 Rev B, 17 Feb 1999, Secure Computing
Corporation, Roseville, MN, USA, February 1999,
<http://www.cs.utah.edu/flux/fluke/html/fspm.ps.gz>.
[RFC1108] Kent, S., "U.S. Department of Defense Security Options for
the Internet Protocol", RFC 1108, DOI 10.17487/RFC1108,
November 1991, <http://www.rfc-editor.org/info/rfc1108>.
[RFC2401] Kent, S. and R. Atkinson, "Security Architecture for the
Internet Protocol", RFC 2401, DOI 10.17487/RFC2401,
November 1998, <http://www.rfc-editor.org/info/rfc2401>.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
December 2005, <http://www.rfc-editor.org/info/rfc4301>.
[RFC5570] StJohns, M., Atkinson, R., and G. Thomas, "Common
Architecture Label IPv6 Security Option (CALIPSO)", RFC
5570, DOI 10.17487/RFC5570, July 2009,
<http://www.rfc-editor.org/info/rfc5570>.
[RFC7204] Haynes, T., "Requirements for Labeled NFS", RFC 7204, DOI
10.17487/RFC7204, April 2014,
<http://www.rfc-editor.org/info/rfc7204>.
Acknowledgments
Ran Atkinson contributed the text for IPSO.
Dave Noveck helped detangle the terminology.
Alexey Melnikov caught that a process was needed for modifying
entries in the registry.
Authors' Addresses
David P. Quigley
EMail: dpquigl@davequigley.com
Jarrett Lu
Oracle
EMail: jarrett.lu@oracle.com
Thomas Haynes
Primary Data, Inc.
4300 El Camino Real Ste 100
Los Altos, CA 94022
United States
Phone: +1 408 215 1519
EMail: thomas.haynes@primarydata.com