Internet-Draft SCHC AC October 2023
Minaburo, et al. Expires 24 April 2024 [Page]
Workgroup:
SCHC Working Group
Internet-Draft:
draft-toutain-schc-access-control-03
Published:
Intended Status:
Standards Track
Expires:
Authors:
A. Minaburo
Consultant
L. Toutain
Institut MINES TELECOM; IMT Atlantique
I. Martinez
Nokia Bell Labs

SCHC Rule Access Control

Abstract

The framework for SCHC defines an abstract view of the rules, formalized through a YANG Data Model. In its original description, rules are static and shared by two endpoints. This document defines defines augmentation to the existing Data Model in order to restrict the changes in the rule and, therefore, the impact of possible attacks.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on 24 April 2024.

1. Introduction

SCHC is a compression and fragmentation mechanism defined in [RFC8724] while [RFC9363] provides a YANG Data Model for formal representation of SCHC Rules used either for compression/decompression (C/D) or fragmentation/reassembly (F/R). The inappropriate changes to SCHC Rules leads to some possible attacks. The goal of this document is to define a augmentation to the existing Data Model in order to restrict the changes in the rules and, therefore, the impact of possible attacks.

2. Conventions and Definitions

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.

3. Terminology

It is expected that the reader will be familiar with the terms and concepts associated with the SCHC framework [RFC8724], [I-D.ietf-schc-architecture], and managmente request processing [I-D.ietf-core-comi], NETCONF[RFC6241], RESTCONF [RFC8040].

ToDo * Access Control. * Management request processing: The NETCONF, RESTCONF or CORECONF request is processed and passed to the end-point Rule Manager. * Rule Manager (RM). * Context. SCHC Rules

4. SCHC TV/MO/CDA possible combinations

SCHC compression behavior uses the TV, MO, and CDA to generate the correct residue. But not all the combinations of this fields descriptors are possible, and then an attack can be detected or avoided. Figure 1 shows all the combinations and those that are enabled. SCHC defines two TV values: set and not set. SCHC MO can be Equal, Ignore, MSB, or Match-mapping. And SCHC CDA can be not-sent, value-sent, mapping-sent, LSB, compute-*, DevIID, or AppIID.

+--------------+----------------------------------------------------+
|              |                      CDA                           |
| TV   /  MO   +--------+---------------+---+---------+------+------+
|              |not-sent| value |mapping|LSB|compute-*|DevIID|AppIID|
|              |        | -sent | -sent |   |         |      |      |
+==============+========+=======+=======+===+=========+======+======+
| set  / Equal |  ok    |absurd |   x   | x | absurd  |absurd|absurd|
+--------------+--------+-------+-------+---+---------+------+------+
|not set /Equal|   x    |   x   |   x   | x | absurd  |absurd|absurd|
+--------------+--------+-------+-------+---+---------+------+------+
| set / Ignore | ok (D) | absurd|    x  | x |   ok    |  ok  |  ok  |
+--------------+--------+-------+-------+---+---------+------+------+
|not set/Ignore|   x    |  ok   |    x  | x |   ok    |  ok  |  ok  |
+--------------+--------+-------+-------+---+---------+------+------+
| set  /   MSB | absurd |absurd |    x  | ok|  absurd |absurd|absurd|
+--------------+--------+-------+-------+---+---------+------+------+
|not set / MSB | absurd | absurd|    x  | ok|  absurd |absurd|absurd|
+--------------+--------+-------+-------+---+---------+------+------+
| set  /  Match|   x    | absurd|   ok  | x |  absurd |absurd|absurd|
|      -mapping|        |       |       |   |         |      |      |
+--------------+--------+-------+-------+---+---------+------+------+
|not set/ Match|   x    |   x   | absurd| x |  absurd |absurd|absurd|
|      -mapping|        |       |       |   |         |      |      |
+--------------+--------+-------+-------+---+---------+------+------+

Figure 1: SCHC TV, MO, CDA valid combinations

5. YANG Access Control

YANG language allows to specify read-only or read write nodes. NACM [RFC8341] extends this by allowing users or groups of users to perform specific actions.

This granularity does not fit this rule model. For instance, the goal is not to allow all the field-id leaves to be modified. The objective is to allow a specific rule entry to be changed and, therefore, some of the leaves to be modified. For instance, an entry with FID containing Uri-path may have its target value modified, as in the same rule, the entry regarding the application prefix should not be changed.

The SCHC access control augments the YANG module defined in [RFC9363] to allow a remote entity to manipulate the rules. Several levels are defined.

  • in the set of rules, it authorizes or not a new rule to be added.

  • in a compression rule, it allows adding or removing field descriptions.

  • in a compression rule, it allows modifying some elements of the rule, such as the TV, MO, or/and CDA, and associated values.

  • in a fragmentation rule, it allows modifying some parameters.

6. YANG Data Model

The YANG DM proposed in Appendix A extends the SCHC YANG Data Model introduced in [RFC9363]. It adds read-only leaves containing access rights. If these leaves are not present, the information cannot be modified.

6.1. leaf ac-modify-set-of-rules

This leaf controls modifications applied to a set of rules. They are specified with the rule-access-right enumeration:

  • no-change (0): rules cannot be modified in the Set of Rules. This is the equivalent of having no access control elements in the set of rules.

  • modify-existing-element (1): an existing rule may be modified.

  • add-remove-element (2): a rule can be added or deleted from the Set of Rules, or an existing rule can be modified.

6.2. leaf ac-modify-compression-rule

This leaf allows to modify a compression element. To be active, leaf ac-modify-set-of-rules MUST be set to modify-existing-element or add-remove-element. This leaf uses the same enumeration as add-remove-element:

  • no-change (0): The rule cannot be modified.

  • modify-existing-element (1): an existing Field Description may be modified.

  • add-remove-element (2): a Field Description can be added or deleted from the Rule or an existing rule can be modified.

6.3. leaf ac-modify-field

This leaf allows to modify a Field Description in a compression rule. To be active, leaves ac-modify-set-of-rules and ac-modify-compression-rule MUST be set to modify-existing-element or add-remove-element and ac-modify-compression-rule and leaf

6.3.1. CoAP base header Access Control.

CoAP protocol uses a request/reply model with compact messages. The format of these messages starts with a fixed format of 4-byte length, followed by a variable Token format with a length between 0 and 8 bytes. While applying SCHC header compression [RFC8824], the based header is only readable and MUST not be modified. Figure 2 shows the access-control for the FID and TV in a Rules.


+----------+--------------+---+--+--+----------+----------+
|   Access |     FID      | FL|FP|DI| Access   |    TV    |
|  Control |              |   |  |  | Control  | (default |
|    FID   |              |   |  |  |    TV    |  value)  |
+----------+--------------+---+--+--+----------+----------+
| Read Only| CoAP.Version | 2 | 1|Bi|Read Only |     1    |
+----------+--------------+---+--+--+----------+----------+
| Read Only| CoAP.Type    | 2 | 1|Bi|Read Only |CON,NON-C,|
|          |              |   |  |  |          |ACK, RST. |
+----------+--------------+---+--+--+----------+----------+
| Read Only| CoAP.TKL     | 4 | 1|Bi|Read/Write|   none   |
+----------+--------------+---+--+--+----------+----------+
| Read Only| CoAP.Code    | 8 | 1|Bi|Read Only |See CoAP  |
|          |              |   |  |  |          |Code      |
|          |              |   |  |  |          |Registries|
+----------+--------------+---+--+--+----------+----------+
| Read Only|CoAP.MessageID| 16| 1|Bi|Read/Write|   none   |
+----------+--------------+---+--+--+----------+----------+
| Read Only|  CoAP.Token  |0-8| 1|Bi|Read/Write|   none   |
+----------+--------------+---+--+--+----------+----------+


Figure 2: Access Control for the CoAP Header

6.3.2. CoAP Options Access Control.

The CoAP options are used by both request and responses messages. Some of them are defined as repeatable which implies that it MAY be included one or more times in a message. In this case, a SCHC Rule MAY be able to modify the FID and the TV in order to include the repetition. The only FID's that have access to be modifiable are those that have been defined as repeatable. The Figure 3 give the control access for all the CoAP Options defined in [RFC7252]; [RFC8613]; [RFC8768]; [RFC9177]; [RFC7959]; and [RFC9175].


+-------+----+--------------+------+---+--+-------+--------+
| Access|CoAP|     FID      |  FL  |FP |DI|Access |   TV   |
|Control|Opt.|              |      |   |  |Control|(default|
|  FID  |Num.|              |      |   |  |  TV   | value) |
+-------+----+--------------+------+---+--+-------+--------+
| Read/ | 1  | CoAP.Option. | 0-8  |var|Bi| Read/ |  none  |
| Write |    | If-Match     |      |   |  | Write |        |
+-------+----+--------------+------+---+--+-------+--------+
| Read  | 3  | CoAP.Option. |      |   |  | Read/ |Sect. 5 |
| Only  |    | Uri-Host     |1-255 |var|Bi| Write | RFC7252|
+-------+----+--------------+------+---+--+-------+--------+
| Read/ | 4  | CoAP.Option. |      |   |  | Read/ |  none  |
| Write |    | ETag         | 1-8  |var|Bi| Write |        |
+-------+----+--------------+------+---+--+-------+--------+
| Read  | 5  | CoAP.Option. |      |   |  | Read  | empty  |
| Only  |    |If-None-Match |  0   | 1 |Bi| Only  |        |
+-------+----+--------------+------+---+--+-------+--------+
| Read  | 6  | CoAP.Option. |      |   |  | Read  |  none  |
| Only  |    | Observe      | 0-3  |var|Bi| Only  |        |
+-------+----+--------------+------+---+--+-------+--------+
| Read  | 7  | CoAP.Option. |      |   |  | Read  |Sect. 5 |
| Only  |    | Uri-Port     | 0-2  |var|Bi| Only  |RFC7252 |
+-------+----+--------------+------+---+--+-------+--------+
| Read/ | 8  | CoAP.Option. |      |   |  | Read/ |  none  |
| Write |    |Location-Path | 0-255|var|Bi| Write |        |
+-------+----+--------------+------+---+--+-------+--------+
| Read  | 9  |CoAP.Option.  |      |   |  | Read  |  none  |
| Only  |    | OSCORE       |0-255 |var|Bi| Only  |        |
+-------+----+--------------+------+---+--+-------+--------+
| Read/ | 11 | CoAP.Option. |      |   |  | Read/ |  none  |
| Write |    | Uri-Path     |0-255 |var|Bi| Write |        |
+-------+----+--------------+------+---+--+-------+--------+
| Read  | 12 | CoAP.Option. |      |   |  | Read  |  none  |
| Only  |    |Content-Format| 0-2  |var|Bi| Only  |        |
+-------+----+--------------+------+---+--+-------+--------+
| Read  | 14 | CoAP.Option. |      |   |  | Read  |   60   |
| Only  |    | Max-Age      | 0-4  |var|Bi| Only  |        |
+-------+----+--------------+------+---+--+-------+--------+
| Read/ | 15 | CoAP.Option. |      |   |  | Read/ |  none  |
| Write |    | Uri-Query    |0-255 |var|Bi| Write |        |
+-------+----+--------------+------+---+--+-------+--------+
| Read  | 16 | CoAP.Option. |      |   |  | Read  |   16   |
| Only  |    | Hop-Limit    |  1   | 1 |Bi| Only  |        |
+-------+----+--------------+------+---+--+-------+--------+
| Read  | 17 | CoAP.Option. |      |   |  | Read  |  none  |
| Only  |    | Accept       | 0-2  |var|Bi| Only  |        |
+-------+----+--------------+------+---+--+-------+--------+
| Read  | 19 | CoAP.Option. |      |   |  | Read  |  none  |
| Only  |    | Q-Block1     | 0-3  |var|Bi| Only  |        |
+-------+----+--------------+------+---+--+-------+--------+
| Read/ | 20 | CoAP.Option. |      |   |  | Read/ |  none  |
| Write |    |Location-Query|0-255 |var|Bi| Write |        |
+-------+----+--------------+------+---+--+-------+--------+
| Read  | 23 | CoAP.Option. |      |   |  | Read  |  none  |
| Only  |    | Block2       | 0-3  |var|Bi| Only  |        |
+-------+----+--------------+------+---+--+-------+--------+
| Read  | 27 | CoAP.Option. |      |   |  | Read  |  none  |
| Only  |    | Block1       | 0-3  |var|Bi| Only  |        |
+-------+----+--------------+------+---+--+-------+--------+
| Read  | 28 | CoAP.Option. |      |   |  | Read  |  none  |
| Only  |    | Size2        | 0-4  |var|Bi| Only  |        |
+-------+----+--------------+------+---+--+-------+--------+
| Read/ | 31 | CoAP.Option. |      |   |  | Read/ |  none  |
| Write |    | Q-Block2     | 0-3  |var|Bi| Write |        |
+-------+----+--------------+------+---+--+-------+--------+
| Read  | 35 | CoAP.Option. |      |   |  | Read  |  none  |
| Only  |    | Proxy-Uri    |1-1034|var|Bi| Only  |        |
+-------+----+--------------+------+---+--+-------+--------+
| Read  | 39 | CoAP.Option. |      |   |  | Read  |  none  |
| Only  |    | Proxy-Scheme |1-255 |var|Bi| Only  |        |
+-------+----+--------------+------+---+--+-------+--------+
| Read  | 60 | CoAP.Option. |      |   |  | Read  |  none  |
| Only  |    | Size1        | 0-4  |var|Bi| Only  |        |
+-------+----+--------------+------+---+--+-------+--------+
| Read  |252 | CoAP.Option. |      |   |  | Read  |  none  |
| Only  |    | Echo         | 1-40 |var|Bi| Only  |        |
+-------+----+--------------+------+---+--+-------+--------+
| Read  |258 | CoAP.Option. |      |   |  | Read  |   0    |
| Only  |    | No-Response  | 0-1  | 1 |Up| Only  |        |
+-------+----+--------------+------+---+--+-------+--------+
| Read  |292 | CoAP.Option. |      |   |  | Read  |  none  |
| Only  |    | Request-Tag  | 0-8  |var|Bi| Only  |        |
+-------+----+--------------+------+---+--+-------+--------+


Figure 3: CoAP Options access-control

7. Normative References

[I-D.ietf-core-comi]
Veillette, M., Van der Stok, P., Pelov, A., Bierman, A., and C. Bormann, "CoAP Management Interface (CORECONF)", Work in Progress, Internet-Draft, draft-ietf-core-comi-16, , <https://datatracker.ietf.org/doc/html/draft-ietf-core-comi-16>.
[I-D.ietf-schc-architecture]
Pelov, A., Thubert, P., and A. Minaburo, "Static Context Header Compression (SCHC) Architecture", Work in Progress, Internet-Draft, draft-ietf-schc-architecture-01, , <https://datatracker.ietf.org/doc/html/draft-ietf-schc-architecture-01>.
[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://www.rfc-editor.org/info/rfc2119>.
[RFC6241]
Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., and A. Bierman, Ed., "Network Configuration Protocol (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, , <https://www.rfc-editor.org/info/rfc6241>.
[RFC7252]
Shelby, Z., Hartke, K., and C. Bormann, "The Constrained Application Protocol (CoAP)", RFC 7252, DOI 10.17487/RFC7252, , <https://www.rfc-editor.org/info/rfc7252>.
[RFC7959]
Bormann, C. and Z. Shelby, Ed., "Block-Wise Transfers in the Constrained Application Protocol (CoAP)", RFC 7959, DOI 10.17487/RFC7959, , <https://www.rfc-editor.org/info/rfc7959>.
[RFC8040]
Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, , <https://www.rfc-editor.org/info/rfc8040>.
[RFC8174]
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <https://www.rfc-editor.org/info/rfc8174>.
[RFC8341]
Bierman, A. and M. Bjorklund, "Network Configuration Access Control Model", STD 91, RFC 8341, DOI 10.17487/RFC8341, , <https://www.rfc-editor.org/info/rfc8341>.
[RFC8613]
Selander, G., Mattsson, J., Palombini, F., and L. Seitz, "Object Security for Constrained RESTful Environments (OSCORE)", RFC 8613, DOI 10.17487/RFC8613, , <https://www.rfc-editor.org/info/rfc8613>.
[RFC8724]
Minaburo, A., Toutain, L., Gomez, C., Barthel, D., and JC. Zuniga, "SCHC: Generic Framework for Static Context Header Compression and Fragmentation", RFC 8724, DOI 10.17487/RFC8724, , <https://www.rfc-editor.org/info/rfc8724>.
[RFC8768]
Boucadair, M., Reddy.K, T., and J. Shallow, "Constrained Application Protocol (CoAP) Hop-Limit Option", RFC 8768, DOI 10.17487/RFC8768, , <https://www.rfc-editor.org/info/rfc8768>.
[RFC8824]
Minaburo, A., Toutain, L., and R. Andreasen, "Static Context Header Compression (SCHC) for the Constrained Application Protocol (CoAP)", RFC 8824, DOI 10.17487/RFC8824, , <https://www.rfc-editor.org/info/rfc8824>.
[RFC9175]
Amsüss, C., Preuß Mattsson, J., and G. Selander, "Constrained Application Protocol (CoAP): Echo, Request-Tag, and Token Processing", RFC 9175, DOI 10.17487/RFC9175, , <https://www.rfc-editor.org/info/rfc9175>.
[RFC9177]
Boucadair, M. and J. Shallow, "Constrained Application Protocol (CoAP) Block-Wise Transfer Options Supporting Robust Transmission", RFC 9177, DOI 10.17487/RFC9177, , <https://www.rfc-editor.org/info/rfc9177>.
[RFC9363]
Minaburo, A. and L. Toutain, "A YANG Data Model for Static Context Header Compression (SCHC)", RFC 9363, DOI 10.17487/RFC9363, , <https://www.rfc-editor.org/info/rfc9363>.

Appendix A. YANG Data Model

<CODE BEGINS> file "ietf-schc-access-control@2023-02-14.yang"

module ietf-schc-access-control {
  yang-version 1.1;
  namespace "urn:ietf:params:xml:ns:yang:ietf-schc-access-control";
  prefix schc-ac;

  import ietf-schc {
      prefix schc;
  }

  organization
    "IETF IPv6 over Low Power Wide-Area Networks (lpwan) working group";
  contact
    "WG Web:   <https://datatracker.ietf.org/wg/lpwan/about/>
     WG List:  <mailto:lp-wan@ietf.org>
     Editor:   Juan-Carlos Zuniga
       <mailto:juancarlos.zuniga@sigfox.com>";
  description
     "
     Copyright (c) 2021 IETF Trust and the persons identified as
     authors of the code.  All rights reserved.

     Redistribution and use in source and binary forms, with or
     without modification, is permitted pursuant to, and subject to
     the license terms contained in, the Simplified BSD License set
     forth in Section 4.c of the IETF Trust's Legal Provisions
     Relating to IETF Documents
     (https://trustee.ietf.org/license-info).

     This version of this YANG module is part of RFC XXXX
     (https://www.rfc-editor.org/info/rfcXXXX); see the RFC itself
     for full legal notices.

     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 (RFC 2119) (RFC 8174) when, and only when,
     they appear in all capitals, as shown here.

     *************************************************************************

     This module extends the ietf-schc module to include the compound-ack
     behavior for Ack On Error as defined in RFC YYYY.
     It introduces a new leaf for Ack on Error defining the format of the
     SCHC Ack and add the possibility to send several bitmaps in a single
     answer.";

  revision 2023-02-14 {
    description
      "Initial version for RFC YYYY ";
    reference
      "RFC YYYY: Compound Ack";
  }

  typedef rule-access-right {
    type enumeration {
      enum no-changes {
        value 0;
        description
          "No change are allowed.";
      }
      enum modify-existing-element {
        value 1;
        description
          "can modify content inside an element.";
      }
      enum add-remove-element {
        value 2;
        description
          "Allows to add or remove or modify an element.";
      }
    }
  }

  typedef field-access-right {
    type enumeration {
      enum no-change {
        value 0;
        description
          "Reserved slot number.";
      }
      enum change-tv {
        value 1;
        description
          "Reserved slot number.";
      }
      enum change-mo-cda-tv {
        value 2;
        description
          "Reserved slot number.";
      }
    }

  }

  augment "/schc:schc/schc:rule" {
    leaf ac-modify-set-of-rules {
          config false;
          type rule-access-right;
        }
  }

  augment "/schc:schc/schc:rule/schc:nature/schc:compression" {
    leaf ac-modify-compression-rule {
          config false;
          type rule-access-right;
        }
  }

  augment "/schc:schc/schc:rule/schc:nature/schc:compression/schc:entry" {
    leaf ac-modify-field {
          config false;
          type field-access-right;
        }
  }

  augment "/schc:schc/schc:rule/schc:nature/schc:fragmentation" {
    leaf ac-modify-timers {
          config false;
          type boolean;
        }
  }


}

<CODE ENDS>

Authors' Addresses

Ana Minaburo
Consultant
Rue de Rennes
35510 Cesson-Sevigne Cedex
France
Laurent Toutain
Institut MINES TELECOM; IMT Atlantique
2 rue de la Chataigneraie
CS 17607
35576 Cesson-Sevigne Cedex
France
Ivan Martinez
Nokia Bell Labs
12 Rue Jean Bart
91300 Massy
France