



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.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   in the Revised BSD License.

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
