Network Working Group L. Seitz Internet-Draft SICS, Swedish Institute of Intended status: Standards Track Computer Science AB Expires: January 7, 2008 E. Rissanen Axiomatics AB July 6, 2007 NETCONF access control profile for XACML draft-seitz-netconf-xacml-00.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on January 7, 2008. Copyright Notice Copyright (C) The IETF Trust (2007). Seitz & Rissanen Expires January 7, 2008 [Page 1] Internet-Draft NETCONF access control profile for XACML July 2007 Abstract The NETCONF remote network configuration protocol currently lacks an access control model. The need for such a model has be recognized within the NETCONF working group. The eXtended Access Control Markup Language (XACML) is an XML-based access control standard, with widespread acceptance from the industry and good open-source support. This document proposes a profile that defines how to use XACML to provide fine-grain access control for NETCONF commands. Table of Contents 1. Requirements notation . . . . . . . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. XACML overview . . . . . . . . . . . . . . . . . . . . . . . . 5 4. NETCONF overview . . . . . . . . . . . . . . . . . . . . . . . 7 5. Policy and Request profile for XACML . . . . . . . . . . . . . 8 5.1. Abbreviations and namespaces . . . . . . . . . . . . . . . 8 5.2. New XACML functions, attributes and data-types . . . . . . 8 5.3. get and get-config RPC . . . . . . . . . . . . . . . . . . 10 5.4. edit-config RPC . . . . . . . . . . . . . . . . . . . . . 13 5.5. copy-config and delete-config RPC . . . . . . . . . . . . 16 5.6. lock and unlock RPC . . . . . . . . . . . . . . . . . . . 19 5.7. kill-session RPC . . . . . . . . . . . . . . . . . . . . . 21 5.8. close-session RPC . . . . . . . . . . . . . . . . . . . . 22 5.9. commit and discard-changes RPC . . . . . . . . . . . . . . 23 5.10. validate RPC . . . . . . . . . . . . . . . . . . . . . . . 24 6. Practical consequences for NETCONF implementations . . . . . . 26 7. Security Considerations . . . . . . . . . . . . . . . . . . . 27 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 28 8.1. Normative References . . . . . . . . . . . . . . . . . . . 28 8.2. Informative References . . . . . . . . . . . . . . . . . . 28 Appendix A. Abbreviations . . . . . . . . . . . . . . . . . . . . 29 Appendix B. Examples . . . . . . . . . . . . . . . . . . . . . . 30 B.1. Get-config example . . . . . . . . . . . . . . . . . . . . 30 B.2. edit-config example . . . . . . . . . . . . . . . . . . . 35 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 41 Intellectual Property and Copyright Statements . . . . . . . . . . 42 Seitz & Rissanen Expires January 7, 2008 [Page 2] Internet-Draft NETCONF access control profile for XACML July 2007 1. Requirements notation The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. Seitz & Rissanen Expires January 7, 2008 [Page 3] Internet-Draft NETCONF access control profile for XACML July 2007 2. Introduction The NETCONF protocol rfc [RFC4741] specifies in its Security Considerations (section 9) that "This document does not specify an authorization scheme, ... Implementors SHOULD provide a comprehensive authorization scheme with NETCONF". In this document a profile is defined and explained that allows to use the eXtended Access Control Markup Language [XACML] as authorization scheme for NETCONF commands. The reasons why the use of XACML is suggested are the following: o XACML is an open standard that has been developed by an industry consortium. o XACML is an XML [XML] based approach, that is well adapted to the authorization challenges encountered within NETCONF. o XACML is widely accepted and used in a number of commercial products [XACMLProducts]. o Open-source implementations of the XACML standard are readily available. Seitz & Rissanen Expires January 7, 2008 [Page 4] Internet-Draft NETCONF access control profile for XACML July 2007 3. XACML overview This section gives a short overview of what XACML is and how it works. We only describe the parts of XACML that are needed in this draft, therefore some descriptions may not reflect the full functionality of the corresponding XACML element. Some familiarity with the terms from [RFC2904] (e.g. PDP, PEP) is expected from the reader. The references also include a more detailed introduction [XACMLIntro]. The XACML standard defines two things: o A XML schema defining a syntax for requests, access control policies and responses. o A processing model that specifies how a request shall be evaluated by a PDP against a set of policies in order to generate a response. A request is a collection of attributes typically describing the requesting subject, the requested resource and the action that the subject wishes to perform on the resource. An attribute can for example be a role of the user or a resource group-id. A policy consists of a target and one or more rules generating an effect. The target describes for which request the policy applies, in terms of conditions on a set of attributes. During evaluation these attributes are fetched from the request and from external information sources (PIPs) available to the PDP. If a policy applies, its effect will either be PERMIT or DENY. An example policy target is shown here: 01 02 03 04 05 print 06 09 10 ... 11 12 ... 13 14 ... 15 Seitz & Rissanen Expires January 7, 2008 [Page 5] Internet-Draft NETCONF access control profile for XACML July 2007 The Target consists of one or more DisjunctiveMatch sections which must all be fulfilled in order for the policy to apply. Within the DisjunctiveMatch section, one of the ConjunctiveMatches must apply. Within a ConjunctiveMatch, all of the Matches must apply. A Match specifies a matching function (which must have a boolean result), and the function parameters, which can either be static AttributeValue (as in line 04) or a value fetched externally from the request of a PIP (as in line 05-07). The AttributeDesignator (lines 05-07) specifies which external value(s) to fetch by giving a Category, an Identifier and a DataType. If several values are returned, only one needs to satisfy the Match function. Seitz & Rissanen Expires January 7, 2008 [Page 6] Internet-Draft NETCONF access control profile for XACML July 2007 4. NETCONF overview The NETCONF configuration protocol describes a set of operations that read or write configuration data on a network device. These operations are transferred to the device by the means of remote procedure calls (RPCs) encoded in XML. The different protocol operations are: o allows to get specific parts of a specific configuration. o allows to edit specific parts of a specific configuration. o allows to overwrite a specific configuration with a new one from a specific source. o allows to delete a specific configuration. o allows to lock a specific configuration for editing. o allows to unlock a specific configuration. o allow to get specific parts from the "running" configuration. o allows to close your own session. o allows to kill someone else's session. For a more specific description of the NETCONF protocol please refer to [RFC4741]. The present document defines an access control model for these operations and for the extensions defined in the standard. Seitz & Rissanen Expires January 7, 2008 [Page 7] Internet-Draft NETCONF access control profile for XACML July 2007 5. Policy and Request profile for XACML The goal of this section is to define how a PEP SHOULD generate a XACML request from a RPC carrying a NETCONF operation. The response to this request determines whether the RPC is processed or discarded. Furthermore this profile defines how policies corresponding to permissions about a specific NETCONF operation on specific data SHOULD be formulated. A strong familiarity with the latest XACML syntax is required to fully appreciate this section. The part of XACML authorisation that deals with the subjects (e.g. in terms of user groups or roles) is out of scope for this profile, since it is not in any way specific to the NETCONF protocol. Thus all the following definitions omit the subject parts of both requests and policies (indicated by "..."). This part can be defined independently from this profile. 5.1. Abbreviations and namespaces Since XML in general, and especially the XACML syntax, are quite verbose we have defined a set of abbreviations, that can be found in section Appendix A. Furthermore we use the term 'Attribute' exclusively for XACML attributes. If we refer to attributes of XML elements we specify this by adding the prefix 'XML' as in 'XML- attribute'. In order to clearly identify new XACML functions, attributes, and data-types defined specifically for this profile they SHALL have the identifier-prefix "xacml-netconf". Thus the following identifiers- prefixes SHALL be used: o Functions: "xacml-netconf:function:" o Attributes: "xacml-netconf:attribute:" o Data-types: "xacml-netconf:data-type:" 5.2. New XACML functions, attributes and data-types This section defines the new functions, attributes and data-types for XACML introduced by this profile. o XACML function: Id="xacml-netconf:function:xpath-node-match" Parameter 1 data-type: &xpath; Parameter 2 data-type: &xpath; The basic idea of this function is to check whether a xml-node in a xml-document is matched by a certain XPath [XPath]. Due to the Seitz & Rissanen Expires January 7, 2008 [Page 8] Internet-Draft NETCONF access control profile for XACML July 2007 difficulty of encoding a xml-node in its document context, we use a second XPath to point to that xml-node in the document. This function works in two steps. First it evaluates the second xpath (representing the xml-node) against the Content element of the Request. This XPath must match a single xml-node only (otherwise an error is returned). In the second step, the first XPath expression is evaluated against the same Content. If the resulting set of xml-nodes contains the xml-node that results from the first step or one of its ancestors, the value of this function is true, otherwise it is false. The following example shall illustrate how this function works: Given the function parameters: /top/interfaces[name="Ethernet"]/interface and /top/interfaces[name="Ethernet"]/interface as well as the content XML document: 01 02 03 Ethernet 04 05 Ethernet0/0 06 1500 07 08 09 Ehternet1/1 10 3000 11 12 13 Ethernet2/2 14 1000 15 16 17 18 WLAN 19 20 DHCP0/0 21 22 23 We get the following evaluation: 1. The second xpath points out the xml-node at line 09. 2. The first xpath points out the xml-nodes 03, 07 and 11. Since xml-node 07 is an ancestor of xml-node 09 the function evaluates to true. Seitz & Rissanen Expires January 7, 2008 [Page 9] Internet-Draft NETCONF access control profile for XACML July 2007 o XACML attribute: Id="xacml-netconf:attribute:rpc-target" Category=&Resource; data-type=&string; This attribute indicates which data store the operation is targeting. In the case of the copy-config command, this is the destination data store. For the lock/unlock commands this is the target data store. An example value would be "running". o XACML attribute: Id="xacml-netconf:attribute:rpc-source" Category=&Resource; data-type=&string; or data-type=&AnyURI; This attribute indicates the source for the operation. In the case of the copy-config command, this is the source data store or an URL. An example value would be "candidate". o XACML data-type: Id="xacml-netconf:data-type:xpath-expression" This data-type is a XPath. The data-type also encodes necessary namespace information, if the XPath is to be used on a namespace aware document. The encoding is an XML-tag with the name of "xpath" containing zero or more attributes, each defining a namespace prefix to namespace URI matching for use with this XPath. An example xpath expression would look like this: 01 02 03 //ns1:top/ns1:interfaces[ns1:name="Ethernet"] 04 05 5.3. get and get-config RPC The get/get-config RPCs get a special treatment, because it was deemed that the whole RPC shouldn't fail just because the the user is not authorised to read parts of the result. Instead the desired behaviour in such a case is to prune the results that are not covered by the users rights. Therefore it is RECOMMENDED to perform access control on the result of a get/get-config RPC instead of on the RPC itself, so that the unauthorised elements can be filtered out and only the authorised ones remain. Requests for get/get-config RPCs SHALL be formed as follows: As a first step, calculate which xml-nodes of the data model are the results of the RPC. For each xml-node in the result, run an XACML request. The request contains Seitz & Rissanen Expires January 7, 2008 [Page 10] Internet-Draft NETCONF access control profile for XACML July 2007 1. The whole result document under the xml-node. 2. A "&Resource;" category Attribute with AttributeId=&resource-id; having the AttributeValue of DataType="&xpath;" which contains an XPath that uniquely identifies the xml-node in question. 3. Another &Resource; category Attribute with AttributeId="xacml- netconf:attribute:rpc-source" and the AttributeValue with DataType="&string;" that identifies the data-model this RPC uses as source (i.e. "running", "startup" or "candidate") corresponding to the RPC source. This SHALL always have a value of "running" for "get" RPCs. 4. An "Action" category Attribute with AttributeId="action-id" and the AttributeValue "read" with DataType="&string;". Each xml-node that is permitted by the corresponding request is included in the result together with its ancestors and descendants. Furthermore the requests for its descendants are skipped. Those xml- nodes that are not permitted are not included. These multiple XACML requests can be executed very efficiently if the PDP is running locally on the network element, preferrably in the same process as the NETCONF agent. Such an architecture would mean that no new XML documents get generated and no network communication needs to be done for those repeated requests. For security reasons it is advisable not to report that parts of the response where pruned by access control, otherwise an attacker could use get/get-config to gather information about the existence of parts of the configuration that is not accessible according to the attackers rights. It is RECOMMENDED that a policy designed to apply to a get or get- config RPC SHOULD match one AttributeValue corresponding to the desired subtree of the data-model with the DataType="&xpath;", the AttributeId="&resource-id;" and the Category="&Resource;". The same element SHOULD contain a match of an AttribueValue corresponding to the desired RPC source (i.e. "running", "startup" or "candidate") with the DataType="&string;", the AttributeId="xacml-netconf:attribute:rpc-source" and the Category="&Resource;". If the policy is to apply to "get" RPCs only this value SHOULD be "running" Furthermore the policy SHOULD match the AttributeValue "read" with the DataType="&string;", the AttributeId="action-id" and the Category="Action". in a element enclosed by a separate element of the policy target. Seitz & Rissanen Expires January 7, 2008 [Page 11] Internet-Draft NETCONF access control profile for XACML July 2007 Example request: 01 02 ... 03 04 05 07 /ns1:top[1]/ns1:interface[1] 08 09 10 11 12 16 17 read 18 19 20 21 22 23 Ethernet0/0 24 1500 25 26 27 Ethernet1/1 28 1000 29 30 31 32 Example policy: Seitz & Rissanen Expires January 7, 2008 [Page 12] Internet-Draft NETCONF access control profile for XACML July 2007 01 02 03 ... 04 05 06 07 08 09 /ns1:top/ns1:interface 10 11 12 15 16 17 running 19 22 23 24 25 26 27 28 read 29 32 33 34 35 36 37 5.4. edit-config RPC Requests for edit-config RPCs SHALL be formed as follows: Under the element an Attribute with the AttributeId="&resource-id;" and the DataType="&xpath;". The AttributeValue SHALL be "//*[@operation and not(ancestor::*[@ operation])]". The same Category SHALL also include an Attribute with the AttributeId="&scope;" and the DataType="&string;". The AttributeValue SHALL be "XPath-expression". Seitz & Rissanen Expires January 7, 2008 [Page 13] Internet-Draft NETCONF access control profile for XACML July 2007 Still under the same Category there SHALL be an Attribute with the AttributeId="xacml-netconf:attribute:rpc-target" and the DataType="& string;". The AttributeValue SHALL be either "running", "startup" or "candidate" corresponding to the RPC target. Furthermore the request SHALL include the element, containing a single Attribute with the AttributeId="action-id" having the DataType="&string;" and the AttributeValue of "write". From the RPC, the contents of the element SHALL be included in the request under the element. If the RPC contains a element the contents of the RPC element that are added to the request element SHALL be edited to add a xml-attribute "operation" with a value corresponding to the value of the element. This request format makes use of the Multiple resource profile of XACML [XACML_MR] where the multiple resources are the elements of the RPC that have an "operation" xml-attribute and no ancestor with such an xml-attribute. Using this profile, no access control is performed for operations that have an ancestor operation. This is due to the fact that all edit-config operations are subsumed under the action "write" as far as access control is concerned. The underlying assumption of this profile is that if you are authorised to write to a xml-node in the data-model you are automatically authorised to write to all its children too. The XPath "//*[@operation and not(ancestor::*[@operation])]" performs the selection of operations with no ancestor operation. If any edit-config operation of the RPC is not permitted, the whole RPC SHALL be denied. If the RPC uses the :url capability (i.e. a element appears instead of the element), the NETCONF agent SHALL preprocess the RPC by downloading the file pointed to by the URL and replacing the element by a element containing the content of the file. Another special case that needs to be treated is the following: According to the protocol specification, it is possible to create a syntactically correct edit-config RPC with no operation at all (i.e. specifying 'none' as and having no 'operation' xml-attributes in the ). Such an RPC SHALL be discarded according to this profile and not be processed by the NETCONF agent, to avoid leaking information with the error messages. It is RECOMMENDED that a policy designed to apply to an edit-config RPC SHOULD match one AttributeValue corresponding to the desired subtree of the data-model with the DataType="&xpath;", the AttributeId="&resource-id;" and the Category="&Resource;". The same element SHOULD contain a match of an AttribueValue corresponding to the desired RPC target (i.e. Seitz & Rissanen Expires January 7, 2008 [Page 14] Internet-Draft NETCONF access control profile for XACML July 2007 "running", "startup" or "candidate") with the DataType="&string;", the AttributeId="xacml-netconf:attribute:rpc-target" and the Category="&Resource;". Furthermore the policy SHOULD match the AttributeValue "write" with the DataType="&string;", the AttributeId="action-id" and the Category="Action" in a element enclosed by a separate element of the policy target. Example request: 01 02 ... 03 04 05 12 16 20 21 write 22 23 24 25 26 27 Ethernet0/0 28 1500 29 30 31 32 Example policy: Seitz & Rissanen Expires January 7, 2008 [Page 15] Internet-Draft NETCONF access control profile for XACML July 2007 01 02 03 ... 04 05 06 07 08 09 /ns1:top/ns1:interface[ns1:name="Ethernet0/0"] 10 11 12 15 16 17 running 19 22 23 24 25 26 27 28 write 30 33 34 35 36 37 38 5.5. copy-config and delete-config RPC Requests for copy-config and delete-config RPCs SHALL be formed as follows: The RPC target parameter SHALL be included under the element as a single Attribute with the AttributeId="xacml-netconf:attribute:rpc-target". If the RPC target is one of {running, startup, candidate} the DataType SHALL be "&string;" otherwise it SHALL be "&AnyURI;". The AttributeValue SHALL be equal to the RPC target. Seitz & Rissanen Expires January 7, 2008 [Page 16] Internet-Draft NETCONF access control profile for XACML July 2007 In case of copy-config RPCs the request SHALL also include the RPC source under same Category as a single Attribute with the AttributeId="xacml-netconf:attribute:rpc-source". If the RPC source is one of {running, startup, candidate} the DataType SHALL be "&string;" otherwise it SHALL be "&AnyURI;". The AttributeValue SHALL be equal to the RPC source. Furthermore the request SHALL include the element, containing a single Attribute with the AttributeId="action-id" having the DataType="&string;". This SHALL have the AttributeValue of "write" if the RPC target is one of {running, startup, candidate}. If the RPC target is a URL then this AttributeValue SHALL be "read". When the target is a URL, no configuration data is overwritten, such RPC must therefore be considered 'read' operations. However when the target is a local configuration, the RPC must be considered a 'write' operation. It is RECOMMENDED that a policy designed to apply to a copy-config/ delete-config RPC SHOULD match one or more AttribueValues corresponding to the desired RPC targets with AttributeId="xacml- netconf:attribute:rpc-target" and the Category="&Resource;". For those targets that are "running", "startup" or "candidate" the DataType SHALL be equal to "&string;", for URL targets, the DataType SHALL be equal to &AnyURI;. Each desired RPC target SHOULD be placed in a separate element under a single common element in the policy target. The policy SHOULD also match one or more AttribueValues corresponding to the desired RPC sources with the DataType="&string;" or DataType="&AnyURI;", the AttributeId="xacml-netconf:attribute:rpc- source" and the Category="&Resource;". Each desired RPC source SHOULD be placed in a separate element under a single common element in the policy target. Furthermore if any target elements where one of {running, startup, candidate}, then the policy SHOULD match the AttributeValue "write" with the DataType="&string;", the AttributeId="action-id" and the Category="Action" in a separate element enclosed by a separate element in the policy target. If any source elements where one of {running, startup, candidate}, then the policy SHOULD match the AttributeValue "read" with the DataType="&string;", the AttributeId="action-id" and the Category="Action" in a separate element. This element should be enclosed the same element as previous "write" action matches if any, otherwise it is to be enclosed by a separate element in the policy target. Seitz & Rissanen Expires January 7, 2008 [Page 17] Internet-Draft NETCONF access control profile for XACML July 2007 Example request: 01 02 ... 03 04 05 08 13 14 write 15 16 17 Example policy: Seitz & Rissanen Expires January 7, 2008 [Page 18] Internet-Draft NETCONF access control profile for XACML July 2007 01 02 03 ... 04 05 06 07 running 09 12 13 14 15 16 17 18 https://user@example.com: 20 passphrase/cfg/new.txt 21 24 25 26 27 28 29 30 write 32 35 36 37 38 39 40 5.6. lock and unlock RPC Requests for lock/unlock RPCs SHALL be formed as follows: The RPC operation target SHALL be included under the element as a single Attribute with the AttributeId="xacml-netconf:attribute:rpc-target" and the DataType="& string;". The AttributeValue SHALL be either "running", "startup" or Seitz & Rissanen Expires January 7, 2008 [Page 19] Internet-Draft NETCONF access control profile for XACML July 2007 "candidate" corresponding to the RPC operation target. Furthermore the request SHALL include the element, containing a single Attribute with the AttributeId="action-id" having the DataType="&string;" and the AttributeValue of either "lock" or "unlock" depending on the type of RPC. It is RECOMMENDED that a policy designed to apply to a lock/unlock RPC SHOULD match one or more AttribueValues corresponding to the desired RPC targets (i.e. "running", "startup" and/or "candidate") with the DataType="&string;", the AttributeId="xacml- netconf:attribute:rpc-target" and the Category="&Resource;". Each desired RPC target SHOULD be placed in a separate element under a single element in the policy target. Furthermore the policy SHOULD match both AttributeValues "lock" and "unlock" with the DataType="&string;", the AttributeId="action-id" and the Category="Action". in separate elements enclosed by a separate element of the policy target. Example request: 01 02 ... 03 04 05 09 10 lock 11 12 13 Example policy: Seitz & Rissanen Expires January 7, 2008 [Page 20] Internet-Draft NETCONF access control profile for XACML July 2007 01 02 03 ... 04 05 06 07 running 09 12 13 14 15 16 17 18 lock 20 23 24 25 26 27 unlock 29 32 33 34 35 36 37 5.7. kill-session RPC Requests and policies for this RPC are defined to be independent of the session-id. Although it would be easily possible to make session-id specific policies and requests, no reasonable use-case for such a feature was found. Any kill-session RPC SHALL be translated to a request that includes the element, containing a single Attribute with the AttributeId="action-id" having the DataType="& Seitz & Rissanen Expires January 7, 2008 [Page 21] Internet-Draft NETCONF access control profile for XACML July 2007 string;" and the AttributeValue "kill-session". It is RECOMMENDED that a policy designed to apply to a kill-session RPC SHOULD match the single AttributeValue "kill-session" with the DataType="&string;", the AttributeId="action-id" and the Category="Action" in a element of its Target. Example request: 01 02 ... 03 04 05 kill-session 07 08 09 Example policy: 01 02 03 ... 04 05 06 07 kill-session 09 12 13 14 15 16 17 5.8. close-session RPC For this RPC it was deemed that no XACML profile was necessary. This results from the assumption that only the person that opened a session should be allowed to submit this RPC to the NETCONF agent. It seems reasonable to expect that the NETCONF agent can enforce this behaviour without the support of the access control system. Seitz & Rissanen Expires January 7, 2008 [Page 22] Internet-Draft NETCONF access control profile for XACML July 2007 5.9. commit and discard-changes RPC If the NETCONF agent supports the :candidate capability, Any commit or discard-changes RPC SHALL be translated to a request that includes the element, containing a single Attribute with the AttributeId="action-id" having the DataType="& string;" and the AttributeValue of either "commit" or "discard- changes". It is RECOMMENDED that a policy designed to apply to a commit or discard-changes RPC SHOULD match the single AttributeValue "commit" or "discard-changes" with the DataType="&string;", the AttributeId="action-id" and the Category="Action" in a element enclosed by a element of its Target. Example request: 01 02 ... 03 04 05 commit 06 07 08 Example policy: 01 02 03 ... 04 05 06 07 commit 09 12 13 14 15 16 17 Seitz & Rissanen Expires January 7, 2008 [Page 23] Internet-Draft NETCONF access control profile for XACML July 2007 5.10. validate RPC If the NETCONF agent supports the :validate capability, requests for lock/unlock RPCs SHALL be formed as follows: The RPC operation target SHALL be included under the element as a single Attribute with the AttributeId="xacml- netconf:attribute:rpc-target" and the DataType="&string;". The AttributeValue SHALL be either "running", "startup" or "candidate" corresponding to the RPC operation target. Furthermore the request SHALL include the element, containing a single Attribute with the AttributeId="action-id" having the DataType="&string;" and the AttributeValue of "validate". It is RECOMMENDED that a policy designed to apply to a validate RPC SHOULD match one or more AttribueValues corresponding to the desired RPC targets (i.e. "running", "startup" and/or "candidate") with the DataType="&string;", the AttributeId="xacml-netconf:attribute:rpc- target" and the Category="&Resource;". Each desired RPC target SHOULD be placed in a separate element under a single element in the policy target. Furthermore the policy SHOULD match the AttributeValue "validate" with the DataType="&string;", the AttributeId="action-id" and the Category="Action" in a separate element enclosed by a separate element of the policy target. Example request: 01 02 ... 03 04 05 09 10 validate 11 12 13 Example policy: Seitz & Rissanen Expires January 7, 2008 [Page 24] Internet-Draft NETCONF access control profile for XACML July 2007 01 02 03 ... 04 05 06 07 candidate 09 12 13 14 15 16 17 18 validate 20 23 24 25 26 27 28 Seitz & Rissanen Expires January 7, 2008 [Page 25] Internet-Draft NETCONF access control profile for XACML July 2007 6. Practical consequences for NETCONF implementations This profile does not make any assumptions on the data-model that a NETCONF operation affects. However writing a correct policy according to this profile requires such knowledge. This is due to the fact that XPathes matching parts of the data-model have to be inserted in the policy. A PDP using this profile to perform access control on NETCONF operations will need access to the RPC and for or operations, to the results of the RPC. No access to actual device data is required by this profile. If a special treatment for get/ get-config proves to be undesirable, a more restrictive interpretation can be implemented by performing a similar access control evaluation as for edit-config RPCs. This profile makes heavy use of XPath [XPath] to reference elements in a data-model. It may be the case that XPath processing proves to be too slow for time-critical applications. Therefore alternatives can be considered, such as the Subtree Filtering proposed in the Netconf standard section 6 [RFC4741]. This profile can be adapted to such alternatives with relative ease, by creating a new data-type for XACML representing the xml-node selection expression and a new function for XACML equivalent to the "xpath-node-match" Function. According to this profile, no specific access control architecture is required (i.e. where the PDP and PEP are implemented). However it seems both advisable and possible to have the PDP running at the same location as the NETCONF agent. Although calls to distant PDPs are possible the response time would be prohibitive. In order to allow for fast communication one should aim to have the PDP running in the same process as the NETCONF agent. Our implementation of the XACML PDP is around 300 KByte large and has a memory consumption in the order of magnitude of 700 KBytes (this is mostly due to XML processing at startup). Further optimisation of these numbers is possible if need arises. If the NETCONF agent supports the :url capability, edit-config RPCs need to be preprocessed to substitute a possible element by a element containing the contents of the file pointed to by the URL. Seitz & Rissanen Expires January 7, 2008 [Page 26] Internet-Draft NETCONF access control profile for XACML July 2007 7. Security Considerations Depending on the error messages returned by unsuccessful edit-config operations, an attacker might probe parts of the data model that are not covered by the attackers access rights. Especially the 'data- exists' and 'data-missing' errors could leak information about the device data. If these leaks are considered severe, one should consider replacing the error message e.g. with an 'operation-failed' error message without further description. New capabilities advertised by NETCONF agents can provide new methods of accessing data on the device. If the access control model does not cover such capabilities it is RECOMMENDED to deny requests using them until the model has been extended to cover them. In order to implement such behaviour for new NETCONF operations, a deny-biased PDP can be used. Such a PDP denies all requests for which no applicable policy can be found. If the capability affects existing NETCONF operations, the specific profile for these operations SHOULD be extended. Security considerations from the XACML standard [XACML] and from the NETCONF standard [RFC4741] SHOULD be applied to any use of this profile. Seitz & Rissanen Expires January 7, 2008 [Page 27] Internet-Draft NETCONF access control profile for XACML July 2007 8. References 8.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2904] Vollbrecht, J., Calhoun, P., Farrell, S., Gommans, L., Gross, G., de Bruijn, B., de Laat, C., Holdrege, M., and D. Spence, "AAA Authorization Framework", RFC 2904, August 2000. [RFC4741] Enns, R., "NETCONF Configuration Protocol", RFC 4741, December 2006. [XACML] OASIS, "eXtensible Access Control Markup Language", . [XACML_MR] Anne, A., "Multiple resource profile of XACML v2.0", OASIS Standard, February 2005. [XML] Bray, T., Paoli, J., Maler, E., Sperberg-McQueen, C., and F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fourth Edition)", World Wide Web Consortium Recommendation REC- xml-20060816, August 2006, . [XPath] DeRose, S. and J. Clark, "XML Path Language (XPath) Version 1.0", World Wide Web Consortium Recommendation REC-xpath-19991116, November 1999, . 8.2. Informative References [XACMLIntro] Sun Microsystems, Inc., "A Brief Introduction to XACML", Webpage http://www.oasis-open.org/committees/download.php/ 2713/Brief_Introduction_to_XACML.html, March 2003. [XACMLProducts] Anderson, A., "XACML References and Products, Version 1.73", Webpage http://docs.oasis-open.org/xacml/xacmlRefs.html, January 2007. Seitz & Rissanen Expires January 7, 2008 [Page 28] Internet-Draft NETCONF access control profile for XACML July 2007 Appendix A. Abbreviations For abbreviating XACML policies and requests this profile provides a list of entity declarations, that is to be used within this document. The syntax and expansion for such entities is defined in [XML] (e.g. &string; will be expanded to "http://www.w3.org/2001/XMLSchema#string"). o o o o o o o o o Seitz & Rissanen Expires January 7, 2008 [Page 29] Internet-Draft NETCONF access control profile for XACML July 2007 Appendix B. Examples In this section we give examples of requests, policies and their evaluation. B.1. Get-config example Given the following get-config RPC: 01 03 04 05 06 07 08 09 10 11 we get the following result before access control: Seitz & Rissanen Expires January 7, 2008 [Page 30] Internet-Draft NETCONF access control profile for XACML July 2007 01 03 04 05 06 Ethernet 07 08 Ethernet0/0 09 1500 10 11 12 Ehternet1/1 13 3000 14 15 16 Ethernet2/2 17 1000 18 19 20 21 WLAN 22 23 WLAN0/0 24 25 26 27 28 Now given and the XACML policy (ommitting the subject part): Seitz & Rissanen Expires January 7, 2008 [Page 31] Internet-Draft NETCONF access control profile for XACML July 2007 01 02 03 ... 04 05 06 07 08 /top/interfaces[name="Ethernet"] 09 10 13 14 15 running 17 20 21 22 23 24 25 26 read 28 31 32 33 34 35 36 we generate the following requests (ommitting the subject part): Seitz & Rissanen Expires January 7, 2008 [Page 32] Internet-Draft NETCONF access control profile for XACML July 2007 01 02 ... 03 04 05 10 14 15 read 16 17 18 19 ... 20 21 which is denied. 01 02 ... 03 04 05 04 05 04 05 04 05 04 05 04 05 03 04 05 06 Ethernet 07 08 Ethernet0/0 09 1500 10 11 12 Ehternet1/1 13 3000 14 15 16 Ethernet2/2 17 1000 18 19 20 21 22 B.2. edit-config example Given the following edit-config RPC: Seitz & Rissanen Expires January 7, 2008 [Page 35] Internet-Draft NETCONF access control profile for XACML July 2007 01 03 04 05 06 07 08 Ethernet 09 10 Ethernet0/0 11 1500 12 192.0.0.1 13 14 15 Ethernet1/1 16 3000 17 18 19 Ethernet2/2 20 1000 21 22 23 24 WLAN 25 26 WLAN0/0 27 28 29 30 31 32 and the following XACML policy (ommitting the subject part): Seitz & Rissanen Expires January 7, 2008 [Page 36] Internet-Draft NETCONF access control profile for XACML July 2007 01 02 03 ... 04 05 06 07 08 /top/interfaces[name="Ethernet"] 09 10 13 14 15 running 17 20 21 22 23 24 25 26 write 28 31 32 33 34 35 36 we generate the following request from the RPC: Seitz & Rissanen Expires January 7, 2008 [Page 37] Internet-Draft NETCONF access control profile for XACML July 2007 01 02 03 04 running 05 06 07 XPath-expression 09 10 11 18 19 write 20 21 22 23 [Contents of the element in the RPC] 24 25 which results in the following XACML response: 01 02 03 Permit 04 05 07 08 /top[1]/interfaces[1]/interface[1] 09 10 11 12 13 14 15 16 17 NotApplicable 18 19 Seitz & Rissanen Expires January 7, 2008 [Page 38] Internet-Draft NETCONF access control profile for XACML July 2007 21 28 29 30 31 Permit 32 33 35 36 /top[1]/interfaces[1]/interface[2] 37 38 39 40 41 42 43 44 45 Permit 46 47 49 50 /top[1]/interfaces[1]/interface[3]/mtu[1] 47 48 49 50 51 52 53 54 The meaning of this response is the following: o The operation on line 09 of the RPC is permitted (lines 02-14 of the response). o There is no applicable policy for the operation on line 25 of the RPC (lines 15-27 of the response). This usually means that we deny the operation and therefore reject the whole RPC. Seitz & Rissanen Expires January 7, 2008 [Page 39] Internet-Draft NETCONF access control profile for XACML July 2007 o The operation on line 14 of the RPC is permitted (line 28-40 of the response). o The operation on line 20 of the RPC is permitted (line 41-53 of the response). The operation on line 12 of the RPC is not submitted to access control since a ancestor xml-element already contained a edit-config operation (line 09). Since we simplify all edit-config operations to 'write', the operation on line 12 would have been permitted anyway as the ancestor operation was permitted. If the ancestor operation had been denied the whole RPC would be rejected anyway. Seitz & Rissanen Expires January 7, 2008 [Page 40] Internet-Draft NETCONF access control profile for XACML July 2007 Authors' Addresses Ludwig Seitz SICS, Swedish Institute of Computer Science AB Box 1263 Kista 164 29 Sweden Phone: +46 8 633 1516 Email: ludwig@sics.se Erik Rissanen Axiomatics AB Ringstedsgatan 36 Kista 164 48 Sweden Email: erik@axiomatics.com Seitz & Rissanen Expires January 7, 2008 [Page 41] Internet-Draft NETCONF access control profile for XACML July 2007 Full Copyright Statement Copyright (C) The IETF Trust (2007). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Seitz & Rissanen Expires January 7, 2008 [Page 42]