Internet Engineering Task Force (IETF) P. Wouters
Request for Comments: 9478 Aiven
Category: Standards Track S. Prasad
ISSN: 2070-1721 Red Hat
October 2023
Labeled IPsec Traffic Selector Support for the Internet Key Exchange
Protocol Version 2 (IKEv2)
Abstract
This document defines a new Traffic Selector Type (TS Type) for the
Internet Key Exchange Protocol version 2 (IKEv2) to add support for
negotiating Mandatory Access Control (MAC) security labels as a
Traffic Selector of the Security Policy Database (SPD). Security
Labels for IPsec are also known as "Labeled IPsec". The new TS Type,
TS_SECLABEL, consists of a variable length opaque field that
specifies the security label.
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 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9478.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction
1.1. Requirements Language
1.2. Traffic Selector Clarification
1.3. Security Label Traffic Selector Negotiation
2. TS_SECLABEL Traffic Selector Type
2.1. TS_SECLABEL Payload Format
2.2. TS_SECLABEL Properties
3. Traffic Selector Negotiation
3.1. Example TS Negotiation
3.2. Considerations for Using Multiple TS Types in a TS
4. Security Considerations
5. IANA Considerations
6. References
6.1. Normative References
6.2. Informative References
Acknowledgements
Authors' Addresses
1. Introduction
In computer security, Mandatory Access Control (MAC) usually refers
to systems in which all subjects and objects are assigned a security
label. A security label is composed of a set of security attributes.
Along with a system authorization policy, the security labels
determine access. Rules within the system authorization policy
determine whether the access will be granted based on the security
attributes of the subject and object.
Historically, security labels used by Multi-Level Secure (MLS)
systems are comprised of a sensitivity level (or classification)
field and a compartment (or category) field, as defined in [RFC5570].
As MAC systems evolved, other MAC models gained popularity. For
example, SELinux, a Flux Advanced Security Kernel (FLASK)
implementation, has security labels represented as colon-separated
ASCII strings composed of values for identity, role, and type. The
security labels are often referred to as security contexts.
Traffic Selector (TS) payloads specify the selection criteria for
packets that will be forwarded over the newly set up IPsec Security
Association (SA) as enforced by the Security Policy Database (SPD)
[RFC4301].
This document specifies a new TS Type, TS_SECLABEL, for IKEv2 that
can be used to negotiate security labels as additional selectors for
the SPD to further restrict the type of traffic that is allowed to be
sent and received over the IPsec SA.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
1.2. Traffic Selector Clarification
The negotiation of Traffic Selectors is specified in Section 2.9 of
[RFC7296], where it defines two TS Types (TS_IPV4_ADDR_RANGE and
TS_IPV6_ADDR_RANGE). The TS payload format is specified in
Section 3.13 of [RFC7296]. However, the term "Traffic Selector" is
used to denote the TS payloads and individual Traffic Selectors of
that payload. Sometimes, the exact meaning can only be learned from
context or if the item is written in plural ("Traffic Selectors" or
"TSes"). This section clarifies these terms as follows:
A Traffic Selector (capitalized, no acronym) is one selector for
traffic of a specific Traffic Selector Type (TS Type). For example,
a Traffic Selector of TS Type TS_IPV4_ADDR_RANGE for UDP (protocol
17) traffic in the IP network 198.51.100.0/24 covering all ports is
denoted as (17, 0, 198.51.100.0-198.51.100.255).
A TS payload is a set of one or more Traffic Selectors of the same or
different TS Types. It typically contains one or more of the TS Type
of TS_IPV4_ADDR_RANGE and/or TS_IPV6_ADDR_RANGE. For example, the
above Traffic Selector by itself in a TS payload is denoted as
TS((17, 0, 198.51.100.0-198.51.100.255))
1.3. Security Label Traffic Selector Negotiation
The negotiation of Traffic Selectors is specified in Section 2.9 of
[RFC7296] and states that the TSi/TSr payloads MUST contain at least
one TS Type. This document adds a new TS Type of TS_SECLABEL that is
valid only with at least one other TS Type. That is, it cannot be
the only TS Type present in a TSi or TSr payload. It MUST be used
along with an IP address selector type, such as TS_IPV4_ADDR_RANGE
and/or TS_IPV6_ADDR_RANGE.
2. TS_SECLABEL Traffic Selector Type
This document defines a new TS Type, TS_SECLABEL, that contains a
single new opaque Security Label.
2.1. TS_SECLABEL Payload Format
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+-------------------------------+
| TS Type | Reserved | Selector Length |
+---------------+---------------+-------------------------------+
| |
~ Security Label* ~
| |
+---------------------------------------------------------------+
Figure 1: Labeled IPsec Traffic Selector
Note: All fields other than TS Type and Selector Length depend on the
TS Type. The fields shown are for TS Type TS_SECLABEL, which is the
selector that this document defines.
TS Type (one octet):
Set to 10 for TS_SECLABEL.
Selector Length (two octets, unsigned integer):
Specifies the length of this Traffic Selector substructure
including the header.
Security Label:
An opaque byte stream of at least one octet.
2.2. TS_SECLABEL Properties
The TS_SECLABEL TS Type does not support narrowing or wildcards. It
MUST be used as an exact match value.
The TS_SECLABEL TS Type MUST NOT be the only TS Type present in the
TS payload, as TS_SECLABEL is complimentary to another type of
Traffic Selector. There MUST be an IP address Traffic Selector Type
in addition to the TS_SECLABEL TS Type in the TS payload. If a TS
payload is received with only TS_SECLABEL TS Types, the exchange MUST
be aborted with an Error Notify message containing TS_UNACCEPTABLE.
The Security Label contents are opaque to the IKE implementation.
That is, the IKE implementation might not have any knowledge
regarding the meaning of this selector other than recognizing it as a
type and opaque value to pass to the SPD.
A zero-length Security Label MUST NOT be used. If a received TS
payload contains a TS Type of TS_SECLABEL with a zero-length Security
Label, that specific TS payload MUST be ignored. If no other TS
payload contains an acceptable TS_SECLABEL TS Type, the exchange MUST
be aborted with a TS_UNACCEPTABLE Error Notify message. A zero-
length Security Label MUST NOT be interpreted as a wildcard security
label.
If multiple Security Labels are allowed for a Traffic Selector's IP
address range, protocol, and port range, the initiator includes all
of these acceptable Security Labels. The responder MUST select
exactly one of the Security Labels.
A responder that selected a TS with TS_SECLABEL MUST use the Security
Label for all selector operations on the resulting TS. It MUST NOT
select a TS_SECLABEL without using the specified Security Label, even
if it deems the Security Label optional, as the initiator has
indicated (and expects) that the Security Label will be set for all
traffic matching the negotiated TS.
3. Traffic Selector Negotiation
If the TSi payload contains a Traffic Selector with TS Type
TS_SECLABEL (along with another TS Type), the responder MUST create
each TS response for the other TS Types using its normal rules
specified for each of those TS Types, such as narrowing them
following the rules specified for that TS Type and then adding
exactly one for the TS Type of TS_SECLABEL to the TS payload(s). If
this is not possible, it MUST return a TS_UNACCEPTABLE Error Notify
payload.
If the Security Label TS Type is optional from a configuration point
of view, an initiator will add the TS_SECLABEL to the TSi/TSr
payloads. If the responder replies with TSi/TSr payloads that
include the TS_SECLABEL, then the Child SA MUST be created and
include the negotiated Security Label. If the responder did not
include a TS_SECLABEL in its response, then the initiator (which
deemed the Security Label optional) will install the Child SA without
including any Security Label. If the initiator required the
TS_SECLABEL, it MUST NOT install the Child SA and it MUST send a
Delete notification for the Child SA so the responder can uninstall
its Child SA.
3.1. Example TS Negotiation
An initiator could send the following:
TSi = ((17,24233,198.51.100.12-198.51.100.12),
(0,0,198.51.100.0-198.51.100.255),
(0,0,192.0.2.0-192.0.2.255),
TS_SECLABEL1, TS_SECLABEL2)
TSr = ((17,53,203.0.113.1-203.0.113.1),
(0,0,203.0.113.0-203.0.113.255),
TS_SECLABEL1, TS_SECLABEL2)
Figure 2: Initiator TS Payloads Example
The responder could answer with the following:
TSi = ((0,0,198.51.100.0-198.51.100.255),
TS_SECLABEL1)
TSr = ((0,0,203.0.113.0-203.0.113.255),
TS_SECLABEL1)
Figure 3: Responder TS Payloads Example
3.2. Considerations for Using Multiple TS Types in a TS
It would be unlikely that the traffic for TSi and TSr would have a
different Security Label, but this specification allows this to be
specified. If the initiator does not support this and wants to
prevent the responder from picking different labels for the TSi/TSr
payloads, it should attempt a Child SA negotiation and start with the
first Security Label only. Upon failure, the initiator should retry
a new Child SA negotiation with only the second Security Label.
If different IP ranges can only use different specific Security
Labels, then these should be negotiated in two different Child SA
negotiations. In the example above, if the initiator only allows
192.0.2.0/24 with TS_SECLABEL1 and 198.51.100.0/24 with TS_SECLABEL2,
then it MUST NOT combine these two ranges and security labels into
one Child SA negotiation.
4. Security Considerations
It is assumed that the Security Label can be matched by the IKE
implementation to its own configured value, even if the IKE
implementation itself cannot interpret the Security Label value.
A packet that matches an SPD entry for all components, except the
Security Label, would be treated as "not matching". If no other SPD
entries match, the (mislabeled) traffic might end up being
transmitted in the clear. It is presumed that other MAC methods are
in place to prevent mislabeled traffic from reaching the IPsec
subsystem or that the IPsec subsystem itself would install a REJECT/
DISCARD rule in the SPD to prevent unlabeled traffic otherwise
matching a labeled security SPD rule from being transmitted without
IPsec protection.
5. IANA Considerations
IANA has added a new entry in the "IKEv2 Traffic Selector Types"
registry [RFC7296] as follows.
+=======+=============+===========+
| Value | TS Type | Reference |
+=======+=============+===========+
| 10 | TS_SECLABEL | RFC 9478 |
+-------+-------------+-----------+
Table 1: IKEv2 Traffic Selector
Types Registry
6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
Kivinen, "Internet Key Exchange Protocol Version 2
(IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
2014, <https://www.rfc-editor.org/info/rfc7296>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
6.2. Informative References
[LABELED-IPSEC]
Latten, J., Quigley, D., and J. Lu, "Security Label
Extension to IKE", Work in Progress, Internet-Draft,
draft-jml-ipsec-ikev2-security-label-01, 28 January 2011,
<https://datatracker.ietf.org/doc/html/draft-jml-ipsec-
ikev2-security-label-01>.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
December 2005, <https://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,
<https://www.rfc-editor.org/info/rfc5570>.
Acknowledgements
A large part of the introduction text was taken verbatim from
[LABELED-IPSEC], whose authors are Joy Latten, David Quigley, and
Jarrett Lu. Valery Smyslov provided valuable input regarding IKEv2
Traffic Selector semantics.
Authors' Addresses
Paul Wouters
Aiven
Email: paul.wouters@aiven.io
Sahana Prasad
Red Hat
Email: sahana@redhat.com
