Labeled IPsec Traffic Selector support for IKEv2

In computer security, Mandatory Access Control usually refers to systems in which all subjects and objects are assigned a security label. A security label is comprised of a set of security attributes. The security labels along with a system authorization policy 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. Traditionally, security labels used by Multilevel Systems (MLS) are comprised of a sensitivity level (or classification) field and a compartment (or category) field, as defined in and . As MAC systems evolved, other MAC models gained in 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 SA as enforced by the Security Policy Database (SPD, see ). This document updates the Traffic Selector negotiation specified in Section 2.9 of . This document specifies a new Traffic Selector Type TS_SECLABEL for IKEv2 that can be used to negotiate security labels as additional selectors for the Security Policy Database (SPD) to further restrict the type of traffic allowed to be sent and received over the IPsec SA.

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 when, and only when, they appear in all capitals, as shown here.

The negotiation of Traffic Selectors is specified in Section 2.9 of where it defines two TS Types (TS_IPV4_ADDR_RANGE and TS_IPV6_ADDR_RANGE). The Traffic Selector payload format is specified in Section 3.13 of . However, the term Traffic Selector is used to denote the traffic selector 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 "TSs"). This section clarifies these terms as follows: A Traffic Selector (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 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 Traffic Selector payload (TS) is a set of one or more Traffic Selectors of the same or different TS_TYPEs, but MUST include at least one TS_TYPE of TS_IPV4_ADDR_RANGE 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))

The negotiation of Traffic Selectors is specified in Section 2.9 of and states that the TSi/TSr payloads MUST contain at least one Traffic Selector type. This document updates the text to mean that the TSi/TSr payloads MUST contain at least one Traffic Selector of type TS_IPV4_ADDR_RANGE or TS_IPV6_ADDR_RANGE, as other Traffic Selector types can be defined that are complimentary to these Traffic Selector Types and cannot be selected on their own without TS_IPV4_ADDR_RANGE or TS_IPV6_ADDR_RANGE. The below defined TS_SECLABEL Traffic Selector Type is an example of this.

This document defines a new TS Type, TS_SECLABEL that contains a single new opaque Security Label.

*Note: All fields other than TS Type and Selector Length depend on the TS Type. The fields shown is for TS Type TS_SECLABEL, the selector this document defines. TS Type (one octet) - Set to [TBD] for TS_SECLABEL, Selector Length (2 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.

The TS_SECLABEL Traffic Selector Type does not support narrowing or wildcards. It MUST be used as an exact match value. If the TS_SECLABEL is present in a TSi/TSr, at least one Traffic Selector of type TS_IPV4_ADDR_RANGE or TS_IPV6_ADDR_RANGE MUST also be present in that TSi/TSr. The Security Label contents are opaque to the IKE implementation. That is, the IKE implementation might not have any knowledge of the meaning of this selector, other than 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 Traffic Selector MUST be ignored. If no other Traffic Selector of TS_TYPE TS_SECLABEL can be selected, a TS_UNACCEPTABLE Error Notify message MUST be returned. A zero length Security Label MUST NOT be interpreted as a wildcard security label. If multiple Security Labels are allowed for a given IP protocol, start and end address/port match, multiple TS_SECLABEL can be included in a TS payload. If the Security Label traffic selector is optional from a configuration point of view, the initiator will have to choose which TS payload to attempt first. If it includes the Security Label and receives a TS_UNACCEPTABLE, it can attempt a new Child SA negotiation without that Security Label. A responder that selected a TS with TS_SECLABEL MUST use the Security Label for all selector operations on the resulting IPsec SA. It MUST NOT select a TS_set with a TS_SECLABEL without using the specified Security Label, even if it deems the Security Label optional, as the initiator TS_set with TS_SECLABEL means the initiator mandates using that Security Label.

This document updates the specification as follows: Each TS payload (TSi and TSr) MUST contain at least one TS_TYPE of TS_IPV4_ADDR_RANGE or TS_IPV6_ADDR_RANGE. Each TS payload (TSi or TSr) MAY contain one or more other TS_TYPEs, such as TS_SECLABEL. A responder MUST create its TS response by selecting one of each TS_TYPE present in the offered TS by the initiator. If it cannot select one of each TS_TYPE, it MUST return a TS_UNACCEPTABLE Error Notify payload. If a specific TS_TYPE (other than TS_IPV4_ADDR_RANGE or TS_IPV6_ADDR_RANGE which are mandatory) is deemed optional, the initiator SHOULD first try to negotiate the Child SA with the TS payload including the optional TS_TYPE. Upon receiving TS_UNACCEPTABLE, it SHOULD attempt a new Child SA negotiation using the same TS but without the optional TS_TYPE. Some TS_TYPE's support narrowing, where the responder is allowed to select a subset of the original TS. Narrowing MUST NOT result in an empty selector for that TS_TYPE.

An initiator could send:

The responder could answer with the following example:

It would be unlikely that the traffic for TSi and TSr would have a different Security Label, but this specification does allow 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 with only the first Security Label first, and upon failure retry a new Child SA negotiation with only the second Security Label. If different IP ranges can only use different specific Security Labels, than these should be negotiated in two different Child SA negotiations. If in the example above, the initiator only allows 192.0.2.0/24 with TS_SECLABEL1, and 198.51.0/24 with TS_SECLABEL2, than it MUST NOT combine these two ranges and security labels into one Child SA negotiation. The mechanism of narrowing of Traffic Selectors with TS_IPV4_ADDR_RANGE and TS_IPV6_ADDR_RANGE does not apply to TS_SECLABEL as the Security Label itself is not interpreted and cannot itself be narrowed. It MUST be matched exactly. Rekey of an IPsec SA MUST only use identical Traffic Selectors, which means the same TS Type and selectors MUST be used. This guarantees that a Security Label once negotiated, remains part of the IPsec SA after a rekey.

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 (mis-labeled) traffic might end up being transmitted in the clear. It is presumed that other Mandatory Access Control methods are in place to prevent mis-labeled 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.

This document defines two new entries in the IKEv2 Traffic Selector Types registry:

[Note to RFC Editor: Please remove this section and the reference to before publication.] This section records the status of known implementations of the protocol defined by this specification at the time of posting of this Internet-Draft, and is based on a proposal described in . The description of implementations in this section is intended to assist the IETF in its decision processes in progressing drafts to RFCs. Please note that the listing of any individual implementation here does not imply endorsement by the IETF. Furthermore, no effort has been spent to verify the information presented here that was supplied by IETF contributors. This is not intended as, and must not be construed to be, a catalog of available implementations or their features. Readers are advised to note that other implementations may exist. According to , "this will allow reviewers and working groups to assign due consideration to documents that have the benefit of running code, which may serve as evidence of valuable experimentation and feedback that have made the implemented protocols more mature. It is up to the individual working groups to use this information as they see fit". Authors are requested to add a note to the RFC Editor at the top of this section, advising the Editor to remove the entire section before publication, as well as the reference to .

The Libreswan Project https://lists.libreswan.org/mailman/listinfo/swan-dev/ A Proof of Concept branch is available for interop testing. Alpha Implements the entire draft using SElinux based labels GPLv2 TBD Libreswan Development: swan-dev@libreswan.org

A large part of the introduction text was taken verbatim from whose authors are J Latten, D. Quigley and J. Lu.