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 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. 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))

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 adds a new TS_TYPE of TS_SECLABEL that is valid only with at least one other type of Traffic Selector. 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.

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 10 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. The TS_SECLABEL Traffic Selector Type MUST NOT be the only TS_TYPE present in the TS payload. If a TS payload is received with only TS_SECLABEL Traffic Selector types, an Error Notify message containing TS_UNACCEPTABLE MUST be returned. 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, the initiator includes all of the acceptable TS_SECLABEL's and the responder MUST select one of them. 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 Security Label will be set for all traffic matching the negotiated TS.

TS_SECLABEL MUST NOT be used without another TS_TYPE in a Traffic Selector Payload, as it does not specify a complete set of traffic selectors on its own. TS_SECLABEL is complimentary to another type of Traffic Selector. There MUST be an IP address Traffic Selector type in addtion to the TS_SECLABEL Traffic Selector type in the Traffic Selector Payload. If the TSi Payload contains a traffic selector for TS_TYPE of TS_SECLABEL (along with another TS_TYPE), the responder MUST create each TS response for the other TS_TYPEs using its normal rules specifed for each of those TS_TYPE, such as narrowing them following the rules specified for that TS_TYPE, and then add 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 traffic selector 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, than the Child SA MUST be created including 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.

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.

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 one new entry in the IKEv2 Traffic Selector Types registry: [Note to RFC Editor (please remove before publication): This value has already bee added via Early Allocation.

[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/ Implementation was introduced in 4.4, but 4.6 or newer should be used beta Implements the entire draft using SElinux based labels GPLv2 No interop testing has been done yet. The code works including different labeled on-demand kernel ACQUIRES. 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. Valery Smyslov provided valuable input regarding IKEv2 Traffic Selector semantics.