RFC 9478

Labeled IPsec Traffic Selector Support for the Internet Key Exchange Protocol Version 2 (IKEv2)

📅 published October 2023, from ietf

RFC 9478: Labeled IPsec Traffic Selector Support for the Internet Key Exchange Protocol Version 2 (IKEv2) 🎀

Okay bestie, let's get into it 💖 Authors: P. Wouters (Aiven) and S. Prasad (Red Hat). Category: Standards Track. Date: October 2023. ISSN: 2070-1721. This one doesn't list anything it obsoletes or updates, so it's a clean slate 🧚

Abstract ✨

Okay so this doc defines a brand new Traffic Selector Type (TS Type) for IKEv2 🦋 It lets you negotiate Mandatory Access Control (MAC) security labels as a Traffic Selector of the Security Policy Database (SPD). Security labels for IPsec are also called "Labeled IPsec," which is so iconic 💅 The new TS Type, TS_SECLABEL, is a variable-length opaque field that holds 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 (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 Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described 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 🌸

Okay so in computer security, Mandatory Access Control (MAC) usually means systems where every subject and object gets assigned a security label. A security label is made up of a set of security attributes. Along with a system authorization policy, the security labels decide who gets access. The rules in that policy decide whether access is granted, based on the security attributes of the subject and the object 👀

Historically, security labels used by Multi-Level Secure (MLS) systems are made of a sensitivity level (or classification) field and a compartment (or category) field, as defined in [RFC5570]. As MAC systems evolved, other MAC models got popular. For example, SELinux, which is a Flux Advanced Security Kernel (FLASK) implementation, has security labels written as colon-separated ASCII strings made of values for identity, role, and type. These security labels are often called 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. It can be used to negotiate security labels as additional selectors for the SPD, which further restricts the type of traffic that is allowed to be sent and received over the IPsec SA. Literally so precise 🎯

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]. Here's the tea though: the term "Traffic Selector" is used to mean both the TS payloads and the individual Traffic Selectors inside them 🫠 Sometimes the exact meaning only comes through from context, or if the word is written in plural ("Traffic Selectors" or "TSes"). So this section clears things up like this:

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 Types TS_IPV4_ADDR_RANGE and/or TS_IPV6_ADDR_RANGE. For example, the Traffic Selector above 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 🎀

Okay this is the important bit 🚨 The negotiation of Traffic Selectors is specified in Section 2.9 of [RFC7296], and it says that the TSi/TSr payloads MUST contain at least one TS Type. This document adds a new TS Type, TS_SECLABEL, that is valid only alongside at least one other TS Type. Meaning it can't be the only TS Type 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. Not optional, periodt 💅

2. TS_SECLABEL Traffic Selector Type 💜

This document defines a new TS Type, TS_SECLABEL, which contains a single new opaque Security Label. Main character energy 👑

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 this document defines.

Here's the breakdown 🧃

  • 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. Strict but make it make sense 🙈

The TS_SECLABEL TS Type MUST NOT be the only TS Type present in the TS payload, as TS_SECLABEL is complementary 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 means the IKE implementation might not know anything about what this selector means. All it has to do is recognize it as a type and treat the opaque value as something to pass along 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. Zero-length labels are a no-go, bestie 🚫

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 considers the Security Label optional. The reason is that the initiator has indicated (and expects) that the Security Label will be set for all traffic matching the negotiated TS. No skipping the label, sorry not sorry 💀

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 for each of those TS Types. That means 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. Big "make it work or say no" energy 🙅‍♀️

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. Cleanup crew activated 🧹✨

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

Okay so it's pretty unlikely that the traffic for TSi and TSr would have a different Security Label 🙈, but this spec lets you specify it anyway, bestie 💅. If the initiator doesn't support that and wants to stop 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. If that fails, 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. Main character energy means keeping those two separate 😤✨

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. Trust the process, the IKE side just compares labels, it doesn't have to read them 🧚

Okay this part is serious, bestie 💀 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. So basically somebody has to be guarding the door, and that's the vibe we're going for 🛡️🌸

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

6.2. Informative References

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. Huge thanks to these legends 🫶

Authors' Addresses 🎀

Paul Wouters Aiven Email: paul.wouters@aiven.io

Sahana Prasad Red Hat Email: sahana@redhat.com

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