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NFSv4                                                          D. Noveck
Internet-Draft                                                    NetApp
Intended status: Informational                             June 18, 2020
Expires: December 20, 2020


                 Security Needs for the NFSv4 Protocols
                 draft-dnoveck-nfsv4-security-needs-00

Abstract

   This document discusses the existing inadequacies in the handling of
   security issues within the NFSv4 protocols and the steps that might
   be taken to correct the situation, including the preparation of new
   standards-track documents updating existing ones.  Because the
   security approach has been and should remain the same for all minor
   versions, it is expected that security for all the NFSv4 protocols
   will be addressed together in a single NFSv4-wide standards-track
   document.

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 December 20, 2020.

Copyright Notice

   Copyright (c) 2020 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
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   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



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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   4
   3.  Requirements Language Usage in this Document  . . . . . . . .   4
   4.  Situation to be Addressed . . . . . . . . . . . . . . . . . .   5
     4.1.  NFSv4 Use Environments to be Addressed  . . . . . . . . .   5
     4.2.  Emergence and Correction of Security Issues . . . . . . .   7
   5.  Major Problems to Address . . . . . . . . . . . . . . . . . .   9
     5.1.  Problems with Security Presentation/Organization  . . . .  10
       5.1.1.  Problems with Presentation of Security Architecture .  10
       5.1.2.  Problems with Security Evaluation . . . . . . . . . .  12
     5.2.  Problems with treatment of AUTH_SYS . . . . . . . . . . .  12
     5.3.  Problems with Confidentiality . . . . . . . . . . . . . .  16
   6.  Framework for Correcting Problems . . . . . . . . . . . . . .  19
     6.1.  Correcting Problems with Regard to Threat Analyses  . . .  19
     6.2.  Correcting Problems with Regard to Use of Normative Terms  20
   7.  Opportunities for Improvement Provided by Recent Work within
       the RPC Layer . . . . . . . . . . . . . . . . . . . . . . . .  21
     7.1.  Opportunities for Improvement in Encryption . . . . . . .  21
     7.2.  Opportunities for Improvement in Authentication . . . . .  22
     7.3.  Opportunities for Improvement when Using RDMA Transports   22
   8.  Issues that Need to be Addressed  . . . . . . . . . . . . . .  23
     8.1.  Threat  Analysis Goals  . . . . . . . . . . . . . . . . .  23
       8.1.1.  Background  . . . . . . . . . . . . . . . . . . . . .  23
       8.1.2.  Issues to be Addressed  . . . . . . . . . . . . . . .  25
     8.2.  NFSv4 Extension Policies  . . . . . . . . . . . . . . . .  25
       8.2.1.  Background  . . . . . . . . . . . . . . . . . . . . .  25
       8.2.2.  Addressing Extension Issues . . . . . . . . . . . . .  26
     8.3.  TLS Encryption Policies . . . . . . . . . . . . . . . . .  27
       8.3.1.  Background  . . . . . . . . . . . . . . . . . . . . .  27
       8.3.2.  Issues to Address . . . . . . . . . . . . . . . . . .  28
     8.4.  Handling of AUTH_SYS  . . . . . . . . . . . . . . . . . .  31
       8.4.1.  Historical Background . . . . . . . . . . . . . . . .  31
       8.4.2.  Background for Existing AUTH_SYS in NFSv4 . . . . . .  32
       8.4.3.  Core Issue to Resolve for AUTH_SYS  . . . . . . . . .  33
       8.4.4.  Need to Better Document and Explain Issues with
               AUTH_SYS  . . . . . . . . . . . . . . . . . . . . . .  33
       8.4.5.  Issues to Address for Existing Use of AUTH_SYS  . . .  35
       8.4.6.  Issues to Resolve for Revised Approach to AUTH_SYS  .  38
     8.5.  Handling of State Protection  . . . . . . . . . . . . . .  42
       8.5.1.  Background  . . . . . . . . . . . . . . . . . . . . .  42
       8.5.2.  Issues to be Addressed  . . . . . . . . . . . . . . .  42
   9.  Steps Going Forward . . . . . . . . . . . . . . . . . . . . .  43



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   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  44
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  44
     11.1.  Security Considerations Section for Eventual NFSv4-wide
            Standards-track Security Document  . . . . . . . . . . .  45
     11.2.  Security Considerations Section for Revised RPC
            Specification Document . . . . . . . . . . . . . . . . .  46
     11.3.  Security Considerations Section for Standard-track
            Document dealing with AUTH_SYS . . . . . . . . . . . . .  47
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  47
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  47
     12.2.  Informative References . . . . . . . . . . . . . . . . .  48
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .  49
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  49

1.  Introduction

   This document will discuss the changes that need to be made in the
   security facilities to be used with NFSv4.  These changes are made
   necessary by the fact that the original goal for NFSv4, that of
   enabling secure use on the internet has not been effectively realized
   and because the current approach to security does not address current
   needs for secure operation in many environments.  This document is
   intended to serve as a resource for the working group, as it creates
   new standards-track documents to address the security issues that
   exist within NFSv4.  These potential documents are listed and the
   likely process of producing them is discussed in Section 9.

   Needed changes are expected to involve use of new transport-level
   security facilities provided within the RPC layer (See Section 7).
   These will involve the encryption of NFSv4 traffic and the potential
   use of client host authentication to improve security when AUTH_SYS
   is used, replacing the security approach specified in [RFC7530] and
   [RFC5661].  For a discussion of issues connected to shifting the
   security approach for existing protocols, see Section 4.2.

   Although most use of NFSv4 is not within the internet, but in more
   restricted local area network environments, it appears that NFSv4
   security, as actually used, needs updating to provide security
   appropriate to the current needs of these environments as well.
   Although restricting physical access to the network on which the
   client and server interact can result in limiting access to users
   associated with a particular organization, this step does not
   eliminate the need for protocol support for secure operation.  The
   specific environments and the corresponding security needs are
   discussed in Section 4.1.






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2.  Requirements Language

   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 BCP 14 [RFC2119] [RFC8174] when,
   and only when, they appear in all capitals, as shown here.

3.  Requirements Language Usage in this Document

   Because this is an informational document, it will generally not make
   normative statements including the keywords discussed in Section 2.
   However, in discussing the existing treatment of security in the
   NFSv4 protocols, there will be occasions in which we include
   quotations (most often direct but sometimes indirect) from existing
   standards-track documents that use these keywords.  In such cases,
   the definitions within BCP 14 [RFC2119] [RFC8174] are to be adhered
   to when the terms appear in all-capitals.

   In addition, we will often use these terms in exploring possible
   changes that might be made in possible future standards-track
   documents dealing with NFSv4 and RPC security.  While these terms do
   not have a normative effect in this context, the meaning of these
   terms remains the same.  These statements will differ from and may
   contradict corresponding existing normative statements for one or
   more of the following reasons:

   o  The original statement, currently normative, was ill-advised and
      might have to change to adequately deal with security issues that
      were not previously dealt with appropriately.

   o  The original normative statement, while appropriate given the
      security needs known at the time it was written, might have to
      change to adequately deal with security issues that were not
      recognized when it was published.

   o  The proposed normative statement deals with the actual or
      potential implementation of features that were not available when
      the earlier standards-track documents were written and approved.

   Any such changes in the set of normative statements applying to
   implementations of a particular NFSv4 minor version require special
   care to avoid creating later difficulties.  Problems might arise
   because:

   o  Some recommended changes might be delayed significantly or never
      implemented by some existing implementations.





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   o  There is a possibility of creating interoperability problems when
      a client is written assuming that a particular server behavior is
      foreclosed (e.g. by a "MUST NOT" or "SHOULD NOT") and a later
      change allows that behavior.

4.  Situation to be Addressed

4.1.  NFSv4 Use Environments to be Addressed

   We will consider a range of network environments and how the type of
   environment affects the need for the features being introduced to
   provide for secure operation.

   1.  Within a data center local area network, there may well be
       sufficient administrative controls over the software running on
       machines with physical access to the network as to make
       additional security features within NFS unnecessary.

       If such a network is physically isolated or has all access to it
       controlled using an appropriately configured firewall, it may be
       acceptable, from a security point of view, to use AUTH_SYS
       without client host authentication, and without encryption,
       assuming all attackers have been excluded from access.

       Although such networks typically do have firewalls, they are
       generally configured to allow significant access, including NFSv4
       access, to traffic originating outside the data center, although
       not outside the owning organization.  In such cases, we
       effectively have a within-organization network, dealt with in
       item 2 below.

   2.  Within a network devoted to a single organization or a single
       site within an organization.  Such networks often have associated
       firewalls configured to exclude access from outside the
       organization, and restrict it inside the organization.

       It had until recently been assumed that, by excluding access to
       those outside the organization, it could be assumed that
       attackers would also be excluded.  However, this approach ignores
       the possibility of insider threats.  Since we feel these threats
       cannot be ignored, the security of NFSv4 needs to be upgraded to
       prevent attacks by insiders, making the security needs in this
       case more like those on the internet.

   3.  Use on the internet is the most challenging.  While secure use on
       the internet was a goal of NFSv4 and steps were taken to achieve
       that goal, the approach required a number of steps, including a
       significant performance penalty and a significantly different



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       approach to systems administration.  Given that those
       administering such systems were unwilling to adapt in this way,
       we now need to meet the goal of secure use on the internet in a
       new way.

       Secure use on the internet requires not only protection of user
       data in-flight from unauthorized disclosure or modification, as
       in case 2 above, but also effort to deal with the possibility of
       extensive external monitoring and denial-of-service attacks.

   4.  Use of NFSv4 to access data located in the cloud poses many of
       issues discussed in item 3 above.  However, in general, the cloud
       service provider is responsible for protecting multiple tenants
       from one another, often involving use of tenant-specific
       credentials.  If the distribution of such credentials is quite
       tightly limited, we can have a situation like that in item 1.
       However, if those credentials are available to a larger group,
       then the situation become like that in item 2, with insider
       threats being a point of concern.

   5.  The use of NFSv4 within cloud-located data centers presents
       different issues.  If access to the NFSv4 service is suitably
       restricted, the situation is quite close to that described in
       case 1, with the physical location of the data center irrelevant.
       However, if there means of external access that are not tightly
       restricted, the situation becomes like that of case 2 above, with
       the possibility of insider threats requiring a security model
       with many similarities to that needed for the environments
       described in item 3.

   As will be discussed below, NFSv4 security, as currently defined, has
   significant security issues in many of the above environments,
   although not in all.  No special provisions will be made for the more
   restricted environments, except where necessary to avoid
   incompatibilities when interacting with existing implementations.

   By focusing on a single set of requirements for all of these
   environments, there will necessarily be occasions in which some
   security-related work is required that is not, strictly speaking,
   needed for the particular environment in which it is used.  However,
   we have endeavored to keep the required effort small, eliminating
   requirements for major administrative changes or compute-intensive
   additions to the processing path.








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4.2.  Emergence and Correction of Security Issues

   The fact that serious security issues exist in many of the
   environment discussed above has made it necessary to consider taking
   the drastic step of modifying security-related recommendations for
   existing protocols.  This situation seems to call for an explanation
   and we will attempt to provide one.

   One possible form this might take would be to explain why [RFC7530]
   and [RFC5661] made erroneous choices, with accompanying commentary
   explaining the choices that should have been made instead.

   Such an explanation does not appear to be possible, since it would
   not have been possible for the authors and approvers of these
   documents to reach the conclusions we have adopted without an
   implausible level of foresight on their part.  This is so even though
   we would not adopt the choices made in [RFC7530] and [RFC5661] today.
   Knowing what was known then, we might well have made the same
   choices, although it is hard not to fault the lack of attention, in
   the relevant documents, to the security consequences of the decisions
   made.

   Although we will call attention in sections below to things which
   might have been done differently, this does indicate that we believe
   that the authors and approvers of these documents, could have arrived
   at conclusions similar to the ones we expect to choose now.  Our
   choices are so different from the ones made previously because they
   take into account the needs of NFSv4 today and take advantage of
   security facilities not available earlier.

   In order to better understand this divergence, we have to look at the
   history of NFS and take note of the context in which assumptions were
   established with regard to security or changes in security guidance
   occurred.  In understanding this history and the choices of
   RFC2119-defined keywords, the constraints on the working group need
   to be understood, as described in Section 6.2

   o  The basic assumptions about security for NFS were established over
      thirty years ago.  At that time, it was generally taken for
      granted that a co-operating set of UNIX kernels would provide a
      uniform infrastructure to govern internode sharing within a
      network.  Within this framework, security concerns focused on
      issues related to the appropriateness of granting or withholding
      of privileges by UNIX kernels and there was little concern for
      network security as understood today.  As a result, NFS
      administrators came to take for granted the use of AUTH_SYS making
      it difficult to restrict its use, despite the security weaknesses
      we perceive in it today.  The assumptions underlying AUTH_SYS fit



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      so well with the way UNIX systems were managed in general led to
      the use of AUTH_SYS becoming so well-entrenched that concrete
      steps to eliminate it or to substantially restrict its use were
      never seriously considered.

   o  When NFSv4 was developed, around twenty years ago, serious steps
      were taken to improve the security situation by requiring the
      implementation of RPCSEC_GSS.  This included support for
      encryption, necessary to support use on the internet.  AUTH_SYS
      was retained as an additional optional means of authentication,
      which would have allowed implementations to drop support at a
      later point, although, as things developed, that became less and
      less likely as use of AUTH_SYS remained quite common.

      While it is possible to interpret the treatment of the matter in
      [RFC3530] as implying that these two (i.e.  RPCSEC_GSS and
      AUTH_SYS) were equivalent and to find fault with that implication,
      it is not clear how different choices would have led to a better
      result.  In particular, attempts to deprecate AUTH_SYS (e.g.  by
      using the phrase "SHOULD NOT") would have been problematic in that
      they might have retarded adoption of NFSv4 rather than enhancing
      adoption of RPCSEC_GSS.

   o  When NFSv4.1 was developed, there appeared to be no reason to
      change the security decisions made for NFSv4.0.  Although it might
      have been possible to change the status of AUTH_SYS in NFSv4.1,
      there was no reason to tie the session architecture to changes in
      security that many implementers would have been unwilling to make.

      The only significant security-related extension was the provision
      made for state protection, which required the server to protect
      clients from one another, apart from the users on whose behalf
      requests were being made.

   o  In the ten years since [RFC5661] was published, there was no way
      to address new security needs without creating an essentially new
      protocol, on the order of NFSv4.1, and there was little interest
      in doing that.  Within the framework established by [RFC8178],
      there was provision for the addition of OPTIONAL features, while
      addressing lingering security issues for existing minor versions
      did not fit in that framework.

   With the above history in mind, we will look at why NFSv4 security
   needs are different today and take advantage of some options that
   were not available on earlier occasions in which NFSv4 security
   decisions were made.





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   o  We have the option of providing better security for AUTH_SYS use
      by implementing client host authentication.

   o  We have the option of providing confidentiality and integrity even
      when RPCSEC_GSS is not used.

   o  We have the option of providing confidentiality and integrity
      universally, without special configuration effort or interfering
      with performance by requiring non-offloadable encryption/
      decryption on the client and server.

   o  We have the option of providing state protection (to prevent
      clients interfering with one another) without the special
      implementation work specified in [RFC5661]

   These options have been made available by the work at the RPC layer
   described in Section 7 while the specifics of having NFSv4 take
   advantage of these options are described in Section 8.

   Providing a new security approach for multiple existing protocols is
   potentially disruptive and due care will need to be taken to avoid
   damaging implementation incompatibilities.  However, as will be
   discussed below, the existing situation, in which serious security
   inadequacies need to be addressed, requires that significant changes
   be made.  It is our expectation that the situation will be resolved
   by the eventual publication of a Standards-track document updating
   [RFC7530] and [RFC5661] and much of this document will concern itself
   with determining how the needed changes can resolve existing security
   issues without undue disruption.

5.  Major Problems to Address

   The problems to be addressed concern the way that security
   information has been conveyed in earlier specifications (discussed in
   Section 5.1) as well as two sets of substantive security weaknesses
   discussed in Sections 5.2 and 5.3.

   Although the inadequacies in the presentation of security issues have
   contributed to prolongation of the substantive weaknesses and will be
   discussed in the latter two sections, there is no reason to believe
   that correction of the presentation problems, will, by itself,
   improve the security situation, since the substantive problems still
   need to be addressed.  Nevertheless, correction of the presentation
   issues is necessary so that the proposed solutions to the substantive
   security issues receive the proper attention and analysis, both now
   in connection with the changes to be proposed, and also going
   forward, as needs change.




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5.1.  Problems with Security Presentation/Organization

   While attention has previously focused on the deficiencies of the
   Security Considerations sections (e.g.  Lack of a threat analysis),
   this is not the only presentation issue that needs to be addressed.

   Problems with the overall presentation of NFSv4 security,
   particularly the discussion of the security architecture will be
   dealt with in Section 5.1.1.

   Problems with the evaluation of NFSv4 security including the lack of
   a threat analysis and the contents of the Security considerations
   sections will be dealt with in Section 5.1.2.

5.1.1.  Problems with Presentation of Security Architecture

   The presentation of the NFSv4 security architecture (for both minor
   versions) focuses on the work done to make RPCSEC_GSS usable in view
   of the basic architectural decisions made in going from NFSv3 to
   NFSv4.  These include the use of NFS4ERR_WRONGSEC and SECINFO to
   allow the server namespace to be carved into regions with the use of
   particular security flavors and services (associated with particular
   quality-of- protection values) required in each one.

   Unfortunately, features added later in the NFSv4.0 development cycle
   were not integrated into the description of the security
   architecture.  A list of such noteworthy features follows.

   Another consequence of the approach taken to writing Security
   Considerations sections has been that these sections may have not
   appropriately highlighted the security implications of new features
   being added to the protocols.

   o  The addition of callbacks to NFS was not accompanied by an
      explanation of how security for callbacks was to be dealt with, It
      was never made clear whether the existing mandate to provide
      support for RPCSEC_GSS applied to reverse-direction operation.
      The fact that there is no reverse-direction complement to
      NFS4ERR_WRONGSEC and SECINFO means that there is no way that the
      client, as a responder, could force use of another flavor if it
      did not provide support for RPCSEC_GSS authentication, in the role
      of a responder.

      The fact that callbacks are normally issued by the server itself
      and not on behalf a specific user, means that the typical function
      of RPCSEC_GSS authentication is not relevant to the application.
      However, if RPCSEC_GSS is used in the forward direction, then the
      mutual authentication of client and server should be adequate to



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      provide authentication of the server to the client, although the
      possibility that an attacker might inject a spurious callback to
      the reverse-direction request stream remains a concern.

      In any case, the absence of mention of reverse-direction
      authentication in a description of the NFSv4 security approach is
      troubling.  The lack of mention in the Security Considerations
      section is noteworthy because this creates a large set of requests
      and responses for which there is no available facility to mandate
      encryption, and that lack could be exploited by monitoring
      attacks.

   o  The addition of pNFS to NFSv4.1 [RFC5661] required that there be a
      means of providing that the proper quality of protection by
      provided by the a pNFS data server implementing the files mapping
      type.  Given that SECINFO is namespace-oriented, it was necessary
      to define SECINFO_NONAME, implementable by the data server, to
      provide this functionality.

      This security-related change, while explained adequately in
      [RFC5661], is not mentioned in the description of the security
      architecture or the Security Considerations section.  As this
      feature does create new threats, it should have been mentioned in
      the Security Considerations section.  Also, this change while
      compatible with the existing NFSv4 security architecture, does
      represent a considerable change to it.  It seems to call for
      special mention in a standards-track document devoted to NFSv4
      security issues.  It makes sense to include it in an introductory
      section providing an overview of the NFSv4 security architecture.

   o  The implementation of sessions in NFSv4.1 [RFC5661] created a
      requirement to protect clients from one another, even when they
      were making requests on behalf of the same user.  Although
      adequate means of dealing with this issue were described in
      [RFC5661], they were OPTIONAL features and implementation has been
      very limited.

      In this case, the additional exposure makes the absence of mention
      of the issue in the Security Considerations section troublesome,
      although its role in the limited implementation of the
      corresponding security features is hard to evaluate at this point.
      In any case, this was a major architectural change to the security
      architecture which requires more attention.  Over the years, there
      has been considerable discussion on the NFSv4 mailing list of the
      lack of authentication of the client, as opposed to the client
      users on whose behalf it is acting, although no work has been
      undertaken to make this a basic element of NFSv4 security.
      Despite the delay, the issue now seems on its way to effective



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      resolution, using the work done in [I-D.ietf-nfsv4-rpc-tls], as
      described in Section 8.5.

   As we have seen, the description of the security architecture of
   NFSv4 is quite limited and a new security document will have some
   gaps to fill.

5.1.2.  Problems with Security Evaluation

   The principal difficulty in the overall approach to security taken in
   the Security Considerations section of [RFC7530] and [RFC5661]
   concerns the absence of a threat analysis within these documents.
   The absence of such an analysis has meant that:

   o  There was no occasion to determine whether the security
      improvements made relative to earlier versions of NFS were
      adequate to realize any particular reasonable interpretation of
      the goal of "secure use on the internet", which goal was never
      clearly defined.

   o  In the absence of a clear goal or a means of testing whether that
      goal had been met, a choice of security facilities was made based
      on their likely availability.  The prevalent assumption that
      security against network-based attacks was not important in most
      NFS environments made it difficult to consider improvements, or to
      forthrightly discuss existing security weaknesses and make plans
      to address them.

5.2.  Problems with treatment of AUTH_SYS

   While [RFC3530], [RFC7530], and [RFC5661] provide for the MANDATORY
   implementation of RPCSEC_GSS, they do not require its use, allowing
   an opportunity for unauthenticated requests to be issued by attackers
   targeting the many NFSv4 servers in which RPCSEC_GSS is not the only
   form of authentication provided, which appears to be the vast
   majority in operation.

   Although there are a number of nominal authentication flavors that
   allow unauthenticated requests to be presented in circumstances in
   which they will typically be executed by the server, AUTH_SYS is of
   greatest importance for a number of reasons:

   o  It is almost universally implemented by existing NFSv4 servers and
      clients.

   o  Unlike AUTH_NONE, whose name gives fair warning that requests are
      not, in fact, authenticated, AUTH_SYS is described as a means of




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      authentication, without clearly addressing the question of what is
      being authenticated, and by whom.

   o  The substance of the server and client implementations are not
      clearly described in standards-track documents, although there is
      some incomplete information on the topic in [RFC5531].

   o  There is no clear and complete description of the security
      consequences of implementing it and using it.

   o  Despite the fact that it was designated "insecure" in [RFC5531],
      it continued to be used heavily by implementations of all NFSv4
      minor versions.

   The common use of AUTH_SYS, which has continued until now, arose from
   the early history of NFS and its development, as part of the RPC
   authentication function, together with NFSv2 [RFC1094] and NFSv3
   [RFC1813].  That approach, in which security was made the
   responsibility of large multi-user clients trusted by the servers,
   might have made sense when it was developed, but, as things changed,
   became less relevant to NFSv4 security needs.

   In the shift to NFSv4, RPCSEC_GSS was added on a mandatory-to-
   implement basis, while AUTH_SYS was left in place as an alternative
   without any effective consideration of the corresponding consequences
   for security.

   A number of common practices which servers have typically used in
   determining whether AUTH_SYS requests would be accepted are mentioned
   in associated standards-track documents (i.e. in [RFC5531],
   [RFC7530], RFC5661 [RFC5661]) often without clear discussion of their
   obvious security weaknesses.

   As a result of the lack of attention to AUTH_SYS, there is no
   standards-track description of its implementation in connection with
   NFSv4.  Nevertheless, the following practices seem to have been
   adhered to in providing whatever security does exist.

   o  A common server practice, deriving from use with earlier versions
      of NFS, has been to limit acceptance of such requests to requests
      from particular known clients, as determined by the source address
      of the request.

      The possibility of address spoofing is not discussed, although the
      Security Considerations section of [RFC7530] does state that this
      is "certainly not a safe model", most likely alluding to this
      possibility.  This recognition is not followed up on to call into
      question the use of AUTH_SYS as an optional security flavor



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      (stated earlier in the form "MAY be implemented").  Instead, it is
      used as justification for the mandatory nature of RPCSEC_GSS
      implementation, with the lack of security when AUTH_SYS is used
      not further mentioned.

   o  Another common server practice is to restrict use of AUTH_SYS
      based on the associated client source port, assuming that this
      assures that the kernel is making the request and that the kernel
      can be trusted.  That assumption has, over time, become more and
      more dubious, undercutting the underlying logic of AUTH_SYS,
      without any recognition of the consequent effect on the
      reasonableness of continued use of AUTH_SYS or other effective
      action to address the issue.

      Appendix A of [RFC5531] refers to this practice as follows:

         It should be noted that use of this flavor of authentication
         does not guarantee any security for the users or providers of a
         service, in itself.  The authentication provided by this scheme
         can be considered legitimate only when applications using this
         scheme and the network can be secured externally, and
         privileged transport addresses are used for the communicating
         end-points (an example of this is the use of privileged TCP/UDP
         ports in UNIX systems -- note that not all systems enforce
         privileged transport address mechanisms).

   o  Many servers do not execute AUTH_SYS requests specifying a user id
      of zero (i.e. root) under that user id or limit such execution to
      a small set of known clients using the source address checking
      referred to above.

      No mention of this practice (generally called "root squashing")
      has been found so far in IETF documents.  Nevertheless, it
      continues to be implemented in connection with IETF-defined
      protocols such as NFSv4, despite this fact.  While it might make
      an attacker's task more complicated, there is little reason to
      assume that an attacker able to assume any identity he chooses
      other than that of root will be effectively prevented from taking
      advantage of the ability to get unauthenticated requests executed,
      when AUTH_SYS is implemented by a target server.

   As can be seen from the above, important elements of AUTH_SYS
   implementations are not specified within current standards-track
   documents in sufficient detail that interoperable implementations
   could be developed using these documents or subjected to a threat
   analysis, even if one were to be attempted.





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   The Security Considerations section of [RFC5531] states that AUTH_SYS
   is "known to be insecure" and further states "AUTH_SYS SHOULD NOT be
   used for services that permit clients to modify data.  Nevertheless,
   AUTH_SYS has been commonly used by NFSv4 clients modifying data since
   NFSv4 was first implemented, while the consequences for security have
   never been addressed.

   Given the security difficulties that use of AUTH_SYS gives rise to,
   we face a choice between two alternatives:

   o  Take steps to eliminate or otherwise minimize use of AUTH_SYS as a
      valid authentication flavor, either for NFSv4 as a whole or for
      minor versions based on NFSv4.1, whose description was published
      as a Proposed Standard after [RFC5531], which stated that AUTH_SYS
      was "known to be insecure".

      Given the many clients using AUTH_SYS, such steps might need to
      take the form of recommendations, with the difficulty of switching
      authentication models considered a valid reason to continue to use
      AUTH_SYS, as long as one is aware of the security consequences.

      Other alternatives are possible and will be discussed later.
      However, regardless of the working group's choice of normative
      terms, it is important that the security consequences of using
      AUTH_SYS are clearly explained.

   o  Revise AUTH_SYS to enable secure implementation of an
      authentication model in which authenticated client hosts are
      assigned the responsibility to determine, within appropriate
      limits, the user ids to be used for each request sent.

      To do this we would authenticate client hosts issuing AUTH_SYS
      requests taking advantage of the authentication provided by
      [I-D.ietf-nfsv4-rpc-tls] as described in Section 7.2.  There is
      also a more detailed discussion of issues to be addressed in
      establishing the rules for this form of authentication in
      Section 8.4.6.

   Although both of these alternatives should be considered, there is
   reason to believe that the first of these is not feasible, for
   reasons similar to those that have prevented such a step being
   attempted earlier, either as part of the transition to NFSv4 or to
   NFSv4.1.  The use of AUTH_SYS has continued despite the fact that
   alternatives were made available, and there is no reason to expect
   that the use of the words "SHOULD NOT" or "MUST NOT" would prevent
   implementers from continuing to support it, or administrators
   depending on such support, despite the negative effect on the
   security of NFSv4 implementations



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   Because of the current predominant role of AUTH_SYS in existing NFSv4
   implementations, providing better security while remaining within the
   AUTH_SYS framework will also be difficult because of the issues
   discussed in Section 6.2.  Nevertheless, we feel it needs to be
   attempted, as a new security framework cannot address AUTH_SYS
   without clearly discussing its security weaknesses.  Once that is
   done, we need to take advantage of the ability to effect client host
   authentication provided by [I-D.ietf-nfsv4-rpc-tls] to provide a
   modicum of security while allowing administrators to delegate
   credential checking to trusted clients as they are now accustomed to
   doing.

   While this approach is far from ideal, in that it requires a trust
   relationship between client and servers, adopting it provides a
   reasonable approach to support NFSv4 in the near-term while allowing
   development of a better alternative (e.g. a new authentication
   flavor) to proceed in parallel.  With regard to our immediate need
   for better NFSv4 security, the obvious alternatives might not be
   realizable:

   o  Given the security weaknesses of AUTH_SYS and the need to present
      a threat analysis, we cannot present AUTH_SYS without client host
      authentication as optional to use, either explicitly or by
      implication.

   o  Recommending that AUTH_SYS without host authentication not be
      used, with RPCSEC_GSS as the only alternative will not be
      effective and would limit adoption of a clearly better, although
      far-from-ideal, alternative

   Despite this summary of the author's views on this matter, this
   question is ultimately a matter for working group decision.  For a
   further discussion of related issues, see Section 8.4.3.  Although
   the rest of this document is written assuming that the author's
   choice will be selected, Section 8.4.3 explains the changes to the
   eventual standards-track document that would be required if different
   choices were to be made.

5.3.  Problems with Confidentiality

   Confidentiality is currently provided within NFSv4 by the use of
   RPCSEC_GSS, with the server charged with enforcing any administrator-
   specified needs to use these facilities on appropriate portions of
   the server namespace.  Requirements for the use of integrity
   protection are handled similarly.  This approach is capable of
   providing confidentiality when accessing certain directories or file
   systems, assuming that files that require such protection can be
   isolated in certain regions of the server namespace.



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   An important difficulty with regard to this approach to
   confidentiality is that there is significant non-encrypted data sent
   on NFSv4 connections which can allow extensive data to be gathered on
   the part of those engaged in monitoring attacks

   o  Certain parts of RPC requests and response are not encrypted and
      can be the basis of traffic analysis.  Fortunately, the structure
      of NFSv4 requests limits the data exposed since the requested
      operation is always COMPOUND (or CB_COMPOUND).  Nevertheless, the
      size of requests and information determinable from those allows
      patterns of reading and writing data by specific clients to be
      inferred.

   o  Because the focus of this approach is on areas of the server
      namespace, there is no way to force use of encryption on requests
      used to set up connections and sessions.

   o  Similarly, there is no provision for negotiating/enforcing the use
      of integrity or encryption on reverse-direction requests.

   Despite the availability of encryption in NFSv4, it is very rarely
   used, which makes its formal sufficiency essentially irrelevant.  In
   understanding why confidentiality is not more generally used, we need
   look at the issues below in order to understand how to address the
   problem going forward.

   o  The cost is such that its use has a noticeable effect on
      performance, given that the design (by requiring different keys
      for different users) makes it difficult or impossible for the work
      of encryption to be offloaded.

      It is likely that, given increasing network speeds, this factor is
      more important today than it was when this approach was settled
      upon.

   o  In many environments it might not be possible to isolate files
      needing such protection in a way consistent with the way file
      protections are normally managed.  As a result, encryption would
      be present for all files or for none, with none being chosen most
      often because of performance concerns.

   o  Implementation of confidentiality requirements may face
      difficulties due to uncertainty about whether client encryption
      support is available.  For example, [RFC7530] specifies that
      privacy support is required (although only for krb5), while
      [RFC5661] says only that clients "SHOULD" support privacy.  The
      document give no guidance regarding what might be considered valid
      reasons to not support privacy, leaving servers without any



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      reliable way of demanding confidentiality on certain portions of
      the server namespace.

   o  The concurrent use of AUTH_SYS might have a similar inhibiting
      effect.  While it is possible, within the protocol, to force a
      transition to use of RPCSEC_GSS with privacy, RPCSEC GSS access
      might not be possible in many cases (e. g. the proper id mapping
      facilities might not have been configured).

   o  The current Security Considerations sections for the NFSv4
      protocols may have contributed to the continuation of the problem
      by not drawing sufficient attention to the security issues
      involved in allowing access without encryption.

   Looking at the relevant Security Considerations sections, we find the
   following:

   o  Although the cost of performing encryption is mentioned as a
      reason not to perform it, there is no discussion of the security
      consequences of not performing it.

   o  Similarly, there is no discussion of the use of integrity services
      in preventing modification of user data in flight and the data
      corruption that attackers could cause when these services are not
      used.

   o  There are a number of references to integrity protection for
      various sort of operations but none connected with the protection
      of user data, possibly suggesting to the reader that this issue is
      not important.  Ironically, while the operations used to obtain
      security requirements for a given portion of the namespace are
      among these mentioned, an attacker could not use these to obtain
      transmission in the clear but would instead cause denial-of-
      service, as would happen the bogus security parameters were
      rejected.

   All of the issues discussed above may have contributed to the lack of
   use of encryption with NFSv4, but the issues of poor performance due
   to the a non-offloadable nature of encryption appears to have had a
   critical role in creating an unsatisfactory situation for a protocol
   where high performance is often of critical importance.

   Once the choice was made to limit encryption to specific file systems
   or directories, there was commonly a perceived need to avoid the cost
   of encryption and the difficulties that approach to the matter led to
   were exacerbated by the lack within the Security Considerations
   sections of information about the damage thus done.  Because there
   was insufficient attention to these issues, effective action to



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   address them was delayed, until the problem could no longer be
   ignored.

   Given these weaknesses with regard to encryption, those needing to
   use NFSv4 outside local area networks often implemented NFSv4 over
   secure tunnels.  As this work proceeded, it served as an inspiration
   for the work done in [I-D.ietf-nfsv4-rpc-tls] that provided the
   opportunity to provide encryption uniformly and potentially with high
   performance.  An overview of steps necessary to address these issues
   appears in Section 7.1

6.  Framework for Correcting Problems

   This section addresses the fundamental issues of the organization and
   presentation of a new security framework.  The complementary issues
   involved in making substantive improvements in NFSv4 security will be
   dealt with in Section 7.

6.1.  Correcting Problems with Regard to Threat Analyses

   Of prime importance is the inclusion of appropriate threat analyses,
   even apart from the requirement (in BCP72 [RFC3552]) that such
   analyses appear in Security Considerations sections.  As we have
   already seen, without such an analysis, there is no way to determine
   whether any security changes adopted are adequate to address NFSv4's
   security difficulties.  In the case of NFSv4, because of its
   complicated history and the conflict between the status of AUTH_SYS
   as specified by the NFSv4 specification documents ([RFC7530],
   [RFC5661]) and that in [RFC5531], there might be multiple analyses,
   located in different places:

   o  Because the security needs of the various minor versions are so
      similar, the bulk of the analysis could appear in an NFSv4-wide
      standards-track document updating [RFC7530] and [RFC5661].

   o  The case of a threat analysis for AUTH_SYS raises a special set of
      issues.  Currently, AUTH_SYS is discussed and declared "insecure"
      within [RFC5531] with no threat analysis appearing within the
      document.  A new threat analysis could appear in the NFSv4-wide
      security document referred to above but the fact that AUTH_SYS
      might be considered as part of RPC rather than of NFSv4, might
      dictate otherwise.  Such an analysis might appear in a document
      updating [RFC5531], or in a new document devoted to that specific
      purpose.  Whichever choice is made, there will be a need for a
      document updating [RFC5531].

   The appropriate location of a threat analysis for AUTH_SYS as
   currently used depends on the question of whether to consider



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   AUTH_SYS as part of RPC, as it formally is, or to transfer
   responsibility to NFSv4, since it was deprecated as insecure in
   [RFC5531], while at the same time embedded as a heavily used optional
   feature for all minor versions of NFSv4, including a new protocol,
   NFSv4.1 published as a Proposed Standard subsequently, in [RFC5661].

   Also relevant to the question of the appropriate location for this
   threat analysis is the question of whether there might be a need for
   a revised treatment of AUTH_SYS including client host authentication.
   The possible existence of such a revised treatment, together with
   issues related to a threat analysis necessary for its inclusion is
   discussed in Section 8.4.4.

6.2.  Correcting Problems with Regard to Use of Normative Terms

   Another important issue concerns the potential need for adjustment of
   inappropriate use of terms defined by RFC2119 [RFC2119], particularly
   any suggestion that use of AUTH_SYS may be validly used without
   important security consequences, as suggested by the current
   understanding that its use is optional.

   However, as desirable as such clarifications might be, it is
   necessary that we be realistic about what such changes can
   accomplish, even if the particular issues cited in Section 3 are
   properly attended to.  Documents can be written to define certain
   implementations as non-conformant, but the ability of any such
   designation to affect implementer behavior is strongly affected by
   circumstances, particularly when the term is a hard one to pin down
   such as "SHOULD" or "SHOULD NOT".

   The ability of such term choices to affect implementer behavior is at
   its maximum when a new protocol is defined.  In this case, the
   specification document formalizes a contract between implementations,
   so that the consequence of not following these terms is a lack of
   interoperability rather the fact that one's implementation may be,
   formally speaking, non-conformant.  In the case of a protocol such as
   NFSv4,intended to build and extend the work of earlier NFS versions,
   the ability of the IETF to affect implementer choices is
   significantly reduced, as interoperability with the existing protocol
   and the existing infrastructure to support it will be of greater
   importance to implementers.  Further, it needs to be recognized that
   when these terms are used to constrain security-related behavior
   rather than interoperability per se, their effect on implementer
   choice is likely to be similarly reduced.

   Although [RFC2119] provides definitions of "SHOULD" and "SHOULD NOT",
   it is difficult to determine the proper interpretation unless it is
   clear what the "valid reasons" that might supersede the



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   recommendation or the expected consequences of doing so.  For this
   reason, when these terms are used in proposed text, we will make such
   matters explicit, where they are not otherwise clear, as suggested by
   Section 7 of [RFC2119].

7.  Opportunities for Improvement Provided by Recent Work within the RPC
    Layer

   The work done to provide TLS support for RPC (in
   [I-D.ietf-nfsv4-rpc-tls]) presents an important opportunity to
   address the substantive security problems described in Sections 5.2
   and 5.3.  While there will be a need to specify appropriate policies
   for its use by NFSv4 as a ULP (see Sections 8.3.2 and 8.4.6 for
   details), the following opportunities present themselves and are
   likely to be taken advantage of:

   o  The use of transport-level encryption is a good way of dealing
      with the inadequacies discussed in Section 5.3.  The use of a
      single key per connection makes offloaded implementations possible
      allowing use for all requests including those currently not
      encrypted.  This is discussed in more detail in Section 7.1

   o  Authentication of the client host, as provided by the
      authentication material presented at connection initialization
      might be used to authenticate the client host, to avoid acceptance
      of AUTH_SYS requests from unauthenticated clients.  This is
      discussed in more detail in Section 7.2

   Although [I-D.ietf-nfsv4-rpc-tls]) does not provide support for RDMA
   transports, parallel services to provide encryption and
   authentication are expected to be available, as discussed in
   Section 7.3.

7.1.  Opportunities for Improvement in Encryption

   [I-D.ietf-nfsv4-rpc-tls] provides the ability to encrypt all traffic
   on the connection used between an NFSv4 client and server.  This
   requires that that both the client and server provide support for
   RPC-over-TLS.  Appropriate requirements/recommendations are discussed
   in Section 8.3.2.

   Because this facility is based on an opportunistic use of TLS, there
   is a need for ULP-defined policies to deal with situations in which
   the server rejected the request for a TLS connection.  These matters
   are discussed in Section 8.3.2 as well, as is the policy that servers
   are to adopt when dealing with a connection on which RPC-over-TLS is
   not requested.




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   Because this new form of encryption is being added to an existing
   protocol, all of these policies are more complicated than would be
   the case for a new protocol, since there might be a need to
   accommodate earlier implementations, which might not have had time to
   be enhanced, while providing the ability to take advantage of
   whatever confidentiality support that might be present for a given
   client and server.

7.2.  Opportunities for Improvement in Authentication

   When establishing a connection, as provided for by
   [I-D.ietf-nfsv4-rpc-tls], authentication material is provided by the
   client and could be used to authenticate the client host to the
   server.

   By using this authentication material to authenticate the client
   host, it would be possible to correct some of the issues discussed in
   Section 5.2.  This would involve clearly specifying how that material
   is to be used, in contrast to the situation for the existing
   AUTH_SYS, for which current documentation (in Appendix A of
   [RFC5531]) is quite limited.  Any such respecification would need to
   be acceptable to those used to using AUTH_SYS while avoiding the
   security issues that make its further use, in the old form,
   inadvisable.

   This could allow the following improvements:

   o  This would avoid dependence on the use of source request IP
      address, which is insecure, given the possibility of address
      spoofing.

   o  Authentication material could be separately defined for user and
      kernel-mode clients to avoid dependence on the outdated privileged
      port mechanism.

   o  More options could be provided to allow limitation of the user ids
      upon behalf of which requests are made, to address the limitations
      of "root squashing".

   The details of how the authentication material could be used are
   discussed Section 8.4.6.

7.3.  Opportunities for Improvement when Using RDMA Transports

   As noted above, [I-D.ietf-nfsv4-rpc-tls]) is not supported on RDMA
   transports, making it necessary to provide appropriate support for
   encryption and client host authentication in other ways.




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   o  Often RNICs used to implement RDMA transports will often implement
      encryption to secure inter-RNIC traffic.  When, as is often the
      case, the inter-RNIC protocols are not standardized, the judgment
      as to the adequacy of the encryption is out-of-scope, from our
      point of view.  However, the client and server could be configured
      to take advantage of this encryption, when it is judged
      appropriate to do so by those responsible.  In addition, the
      transport characteristics mechanism defined in
      [I-D.ietf-nfsv4-rpcrdma-version-two] could allow those configuring
      the client and server to make independent judgments on encryption
      adequacy, with RPCSEC_GSS integrity and encryption only
      superseded, when both agree.  (See Section 8.3.2 for details).

   o  Authentication material to support client host authentication can
      be provided by using the transport properties mechanism provided
      for in [I-D.ietf-nfsv4-rpcrdma-version-two].

   It should be noted that our need to normatively reference
   [I-D.ietf-nfsv4-rpcrdma-version-two] would affect the schedule of a
   standards-track document dealing with NFSv4 security.  Given that the
   current milestone for requesting publication is December 2020, this
   not expected to pose an obstacle.

8.  Issues that Need to be Addressed

   These sections discuss the issues that need to be addressed by new
   standards-track documents including both issues of the presentation/
   evaluation of NFSv4 (discussed in Section 5.1) and the substantive
   security weaknesses discussed in Sections 5.2 and 5.3.  For each
   issue there is a section providing background followed by information
   suggesting how the issue would be addressed or issues that would need
   to be resolved before the issue could be addressed.

8.1.  Threat Analysis Goals

8.1.1.  Background

   For reasons that remain unclear, none of the specification documents
   for the existing NFSv4 minor versions contain a threat analysis.  As
   a result, for the reasons discussed in Section 5.1, we need to
   provide an appropriate threat analysis for all NFSv4 minor versions.
   Because of the high degree of overlap between pairs of NFSv4 minor
   versions, most of the analysis will be common to all versions.
   However, there are some areas where features in later minor versions
   have significant security implications:

   o  In NFSv4.1 [RFC5661], SECINFO_NO_NAME was added, in large part
      because it would be necessary to allow the data server, when the



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      pNFS file mapping type is used, to communicate to the client that
      either integrity or encryption would be required when access to
      file data was provided through the data server (as opposed to the
      metadata server).

      The use of TLS-based encryption, which we expect to be recommended
      (see Section 8.3.2, may limit the need for this feature, but it
      will remain REQUIRED, when file-based pNFS is implemented.

   o  NFSv4.1 [RFC5661] facilities were added to protect locking and
      session-related state from modification by other servers (i.e.
      SP4_MACHCRED and SP4_SSV).

      These features have had very limited implementation work, so it
      would be desirable to provide alternative means to achieve the
      goal, as described in Section 8.5.

   While the bulk of the threat analysis would be minor-version-
   independent, differences between minor version will have to be noted,
   as will differences that reflect uses of the facilities discussed in
   Section 7.

   Beyond the lack of NFsv4 threat analyses, there is a further problem
   in that there is no threat analysis dealing with the AUTH_SYS case in
   the existing RPC specification, RFC5531 [RFC5531].  In this case, the
   gap is easier to understand since RPC deals with security on a per-
   flavor basis and declares AUTH_SYS as "insecure".  It may well be
   that the authors, the working group and the IESG thought this was
   adequate, and it would have been if this had resulted in its not
   being used subsequently.  As things happened however, AUTH_SYS
   continued to be used extensively, including for NFsv4, so that there
   still remains a gap in this regard.

   The following facts are relevant to the continued use of AUTH_SYS
   despite its security problems:

   o  It was stated that AUTH_SYS "SHOULD NOT" be used for services
      capable of modifying data.  Given that its further use was still
      anticipated, in some circumstances, a security analysis would
      still be required.  In addition, use within the purview of the
      "SHOULD NOT" would make such analysis even more important, since
      that recommendation would allow use presumably based on balancing
      of possible benefits and corresponding problems.  Without an
      understanding of the security problems (i.e. the substance behind
      the designation of AUTH_SYS as insecure), such balancing would not
      be possible.





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   o  Despite the recommendation that AUTH_SYS not be used for services,
      such as NFSv4, that are capable of modifying data, NFSv4 was
      specified allowing such use with very limited attention to the
      security issues that uses of AUTH_SYS gives rise to.  As a result,
      there remains a needs for an appropriate threat analysis including
      for AUTH_SYS, since no matter what the working group decides to do
      in this area, use of AUTH_SYS, in connection with all NFS
      protocols (and possible other ONCRPC protocols) will continue for
      some time.

   o  The reason stated for considering AUTH_SYS insecure, the lack of a
      verifier, while worthwhile to note, does not touch the substance
      of the problem, that unauthenticated requests are accepted and
      potentially acted upon.  The difficulty is further compounded by
      the fact that the client validation checks made by actual
      implementations are not fully described within RFC (They are
      described above in Section 5.2)

8.1.2.  Issues to be Addressed

   It is expected that a threat analysis dealing with all NFSv4 minor
   will be dealt with in new standards-track document dealing with NFSv4
   security.  Because this document will address security for all minor
   versions, it will update [RFC7530], [RFC5661], and [RFC7862].

   There will, in addition, be a need for a threat analysis dealing with
   AUTH_SYS, which might or might not appear in the NFSv4-wide security
   document for reasons explained in Section 6.1.  The question of where
   this best be done is discussed in Section 8.4.4.

8.2.  NFSv4 Extension Policies

8.2.1.  Background

   The basic framework for the extension of NFSv4 was established by
   [RFC8178].  Given that the anticipated standards-track document
   dealing with NFSv4 security will, in a sense, extend NFSv4, there
   might be some uncertainty about whether the changes anticipated are
   in line with that extension framework and whether there might be a
   need for that document to update [RFC8178].

   The following questions need to be addressed:

   o  Whether the changes in policies anticipated here, with regard to
      encryption and use of AUTH_SYS, are consistent with [RFC8178].

   o  How the use of new security-related facilities provided at the RPC
      level relates to the extension framework established by [RFC8178].



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   o  How further extensions might relate to use of such new RPC-level
      facilities.

8.2.2.  Addressing Extension Issues

   We anticipate that the material would be in a section entitled,
   "NFSv4 Security Changes and the Existing NFSv4 Extension Model"

   The following introductory material seems appropriate:

      The security-related changes recommended in this document are
      outside the scope of the extension model presented in [RFC8178].
      However, they do not contradict it and there is no need for this
      document to update that one.

      Normally, changes requiring coordinated work on the client and
      server are signaled using a new minor version.  In that case, the
      new minor version is essentially treated as a new protocol and
      there is no need to update [RFC8178] or specifications for
      existing minor versions.

   The following paragraphs discuss the core issues:

      That approach is not possible in this case since the basic need is
      to change the handling of existing minor versions to improve
      security.  This create the possibility of interoperability issues
      since there is neither a new minor version nor a means of
      distinguishing a consistent set of OPTIONAL features supported by
      the server and known to the client.

      In order to limit the possibility of interoperability issues, the
      security changes are made in the form of recommendations, but,
      because there exist implementations built before these
      recommendations were in effect, clients and server have to be
      aware of the possibility that these recommendations might not be
      followed.  As a result, the effect of these recommendations, made
      to limit security issues, is, from an interoperability point of
      view, similar to those that might arise from OPTIONAL features.
      With regard to the NFSv4 extension framework,

      *  The use of the new RPC-level facilities does not raise any
         extension issues, since the existing specification do not limit
         the transport used, except to require reliable and in-order
         delivery.  For this reason, these facilities can be used
         without updating the existing minor version specifications.

         Use of these facilities does not raise additional
         interoperability issues since [I-D.ietf-nfsv4-rpc-tls], by



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         using the opportunistic TLS model, provided for
         interoperability between those that do and do not support these
         extensions.

      *  The policies to use these facilities, made the responsibility
         of the ULP by [I-D.ietf-nfsv4-rpc-tls] are significant
         additions to existing minor versions, requiring that the new
         standards-track document dealing with NFSv4 security update
         [RFC7530] and [RFC5661].

         These changes do not raise interoperability issues since the
         policies apply to all uses of these transport-level facilities
         for NFSV4.  That addresses the case in which client and server
         both provide support while other cases are dealt with as
         indicated in the previous bullet.

      *  The new recommendations regarding use of existing features
         (e.g. encryption, AUTH_SYS) often contradict existing guidance
         and so also require that new standards-track document dealing
         with NFSv4 security update [RFC7530] and [RFC5661].

         These change do potentially raise interoperability issues which
         need to be dealt with by giving sufficient scope, within the
         framework of new recommendations, to accommodate existing
         behavior.  As a result, from an interoperability standpoint,
         these changes are compatible with the previous designation of
         OPTIONAL use, even though the security consequences make it
         necessary that the use of these previously OPTIONAL facilities
         (e.g. transferring data in the clear, use of AUTH_SYS without
         client host authentication) be something to be warned against.

8.3.  TLS Encryption Policies

8.3.1.  Background

   As discussed in Section 5.3, NFSv4 as currently defined, has serious
   problems providing the appropriate level of confidentiality for its
   transmissions.  Providing encryption at the transport layer, whether
   as described in Section 7.1 or otherwise, can be expected to resolve
   this issue by providing encryption in a potentially offloadable way,
   making use of RPC-level privacy and integrity services unnecessary.

   If we were defining a new protocol, such transport-level encryption
   could be REQUIRED without difficulty.  However, given that we are
   upgrading the security for an existing protocol, it might not be
   possible to designate this encryption as "REQUIRED", since this might
   give rise to extensive interoperability problems between new and old
   implementations.  In any case, existing implementers of the existing



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   protocol would not have the same interest in specification compliance
   as in the corresponding situation with a new protocol, leading to a
   situation in which one group of implementations essentially ignored
   the issue of specification-compliance with regard to the latest
   protocol specifications.

   We need to be aware that,

   o  In implementation of a new protocol, any requirements on the
      client the server such as we have been discussing act
      synergistically to marginalize non-compliant implementations.
      Since non-compliant server will not interoperate with a compliant
      client and vice versa.

   o  The corresponding case of a requirement providing for a security
      upgrade, as in this case, is different.  Implementers, and those
      charged with allocating resources to their work will naturally
      focus on improvement/maintenance of the working protocol and limit
      the effort devoted to being the first to do an implementation that
      would not be used until others do their part.  In such cases, if
      there are parties who are not convinced of the necessity for the
      upgrade, it takes strong input from users/customers to ensure that
      the needed upgrade is given sufficient attention.

   o  In some cases, a new protocol containing an important security
      upgrade can result in a situation more like the latter case than
      the former.

   As we consider how to discuss the need for encryption in
   Section 8.3.2, we will be mindful of the above.  Since it not
   possible to REQUIRE encryption, we will RECOMMEND it.  However, in
   discussing the valid reasons that encryption might not be provided,
   we will try to restrict them to the degree we can reasonably do so.
   Further, we will try to clearly state the security consequences which
   implementers and those configuring clients and server need to be
   aware of when choosing to not provide the RECOMMENDED encryption.

8.3.2.  Issues to Address

   There is a need to recommend the implementation and use of
   appropriate encryption by the server and client, as is done, for
   example, by the following paragraphs.

      Data sent over connections used to connect an NFSv4 client and
      server SHOULD be encrypted, whether this uses TLS encryption, as
      described in [I-D.ietf-nfsv4-rpc-tls] (to be used for TCP
      connections) or another form of encryption.  For example,
      [I-D.ietf-nfsv4-rpc-tls] does not address encryption for RPC-over-



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      RDMA ([RFC8166], [I-D.ietf-nfsv4-rpcrdma-version-two]) but RNICs
      used to implement RDMA transports will often implement encryption
      to secure inter-RNIC traffic.

      Valid reasons for not implementing the encryption recommendation
      include insufficient time and resources to code, test, and deploy
      an appropriate implementation.  Implementers and those deploying
      NFSv4 servers and clients and those deploying NFSv4 services need
      to remain aware of the consequences of not providing encryption.
      These consequences are of concern regardless of the validity of
      the reasons for not doing so, which may be expected to become more
      restricted as time goes on.

      Given that it is necessary for both the client and the server to
      provide implementations capable of transport-level encryption,
      those deploying NFSv4 implementations need to be aware of possible
      steps to provide remediation, the difficulties involved in
      providing it and the consequences of not doing do.

      The lack of encryption for the connection as a whole can be
      addressed by encryption of individual requests using the
      facilities within RPCSEC_GSS specified in [RFC7530] and [RFC5661]
      as providing "privacy".  When doing so, the following complicating
      issues need to be taken account of:

      *  Such facilities are not likely to be offloadable and often will
         reduce performance dramatically.

      *  Support for confidentiality via encryption is not required by
         [RFC5661] but only recommended, saying it "SHOULD be
         supported"> Unfortunately, the document does not specify what
         might be valid reasons not to provide such support.  Also,
         although [RFC2119] states the one choosing not to follow such a
         recommendation should be aware of the consequences, given the
         general reticence of NFSv4 specification Security
         Considerations sections about such matters, it is not clear
         that implementers have been able to properly consider the issue
         in the past.  In any case, implementations without such support
         probably exist, making encryption unavailable for some existing
         client-server pairs.

      When encryption is not provided, or, because of its effect on
      performance, not used, all of the user data read or written is
      transmitted in the clear, subject to interception or modification
      in flight.  While this is clearly unacceptable for use on the
      internet, it should not be assumed that it is acceptable in more
      restricted environments.




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      Where this problem exists, it will often be necessary to restrict
      such traffic to specific network segments, and make it impossible,
      via administrative measures, to limit access to such network
      segments or monitor them extensively.

   Although, as indicated in [I-D.ietf-nfsv4-rpc-tls], that there should
   be no need to negotiate security flavors to be used to provide
   integrity and confidentiality, the exact effect on existing clients
   and servers needs to be made clearer.

   The text below is a suggested way of doing this.

      Although the pseudo-flavors created to indicate use of integrity
      or encryption continue to be a part of NFSv4, when transport-level
      encryption is provided, their use is unnecessary, although server
      responses to SECINFO and SECINFO_NONAME may continue to include
      them.

      When TLS is used to provide encryption, as specified in
      [I-D.ietf-nfsv4-rpc-tls], the client and server will, as indicated
      by that document, be aware that encryption, is present.  In the
      case of RPC-over-RDMA, when the RNICs provide encryption
      transparently, the server and client have the opportunity to each
      make their own judgment about the adequacy of the encryption
      provided and communicate this to their peer as a transport
      property as provided for by [I-D.ietf-nfsv4-rpcrdma-version-two]).
      In either case, the client and server will only act, as described
      below, on knowledge about the existence of encryption shared by
      both parties:

      *  The server treats all requests as being made requesting
         encryption, even if a different pseudo-flavor is used.  As a
         result, the server will never return, NFS4ERR_WRONGSEC because
         of a quality-of-protection issue, despite a possible mismatch
         between the pseudo-flavor specified in SECINFO response and the
         one actually used.

         The server will still return NFS4ERR_WRONGSEC when an
         inappropriate security flavor or oid is used and clients need
         to be prepared to use SECINFO to determine the security to be
         used.

      *  The client is free to ignore the quality-of-protection issues
         in a SECINFO response, making use of authentication-only
         variant of RPCSEC_GSS most efficient.






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      *  Although use of integrity or privacy pseudo-flavors is
         unnecessary on an encrypted channel, the server still needs to
         accept such requests.

      *  Within NFSv4.1 [RFC5661], support for SECINFO_NONAME is still
         REQUIRED when pNFS is supported, even if the server only
         accepts connection on which encryption is used, making
         generation of NFS4ERR_WRONGSEC on a connection to the metadata
         server impossible.

8.4.  Handling of AUTH_SYS

8.4.1.  Historical Background

   During the development of NFSv2 [RFC1094], little attention was
   directed to network security and no attention was directed to the
   possibility that a machine on the network might represent itself as a
   client, with the ability to make requests on behalf of non-existent
   client processes it identified by user id.  During this time, NFS
   clients were multi-user machines and it made sense to many for the
   client kernel to have the same responsibilities to verify user
   credentials and keep track of process user ids as it had successfully
   been doing with local file systems.  This was the origin of AUTH_UNIX
   (later renamed AUTH_SYS) which was based on a model of co-operating
   UNIX kernels and provided no protection against an attacker with
   kernel privileges.  Despite the later name change, actual
   implementations were strongly focused on UNIX, deriving the necessary
   implementation requirements from shared code and from informal inter-
   developer communications, rather than standards documents.  As a
   result, as discussed in Section 5.2, when it was necessary to discuss
   the security of AUTH_SYS in connection with RPC (in [RFC5531], there
   was insufficient information on which to base a threat analysis,
   although it was correctly concluded that the result of use was a lack
   of security.

   With regard to the following aspects of AUTH_SYS, this UNIX
   orientation was significant.  In many cases as the computing
   environment changed, it was not possible to change the details to
   keep up with evolving needs.

   o  As the assumption of kernel trustworthiness became increasingly
      unviable as a basis for security, no action was taken to address
      the issue.  While the check for a privileged port retained some
      residual value, it was used to exclude requests issued by non-
      kernel clients as inherently untrustworthy.  The more significant
      and difficult problem of distinguishing trustworthy and
      untrustworthy kerenel-level access was never addressed, leaving




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      AUTH_SYS of little value as a means of authentication, despite its
      continuing use.

   o  AUTH_SYS was focused on the use of the non-hierarchical 32-bit
      user id space typical of UNIX.  Although later attempts were made
      to generalize this within NFSv4, the fact that this approach is
      embedded in many server filesystems meant that this aspect of
      AUTH_SYS, does not seriously obstruct access to such servers.

   o  The particular user id of zero (denoting "root" in UNIX) was often
      treated specially, by treating the request as issued by the
      predefined user id "nobody".  While this was undoubtedly helpful
      when first defined, it is now the case that other non-root users
      might have significant privileges and that the ability of an
      attacker to assume any chosen user id allows much important
      information to be obtained and corrupted.

   Later, with the development of NFSv3 [RFC1813], some of these
   assumptions started to seem less justifiable and alternate
   authentication models were developed.  However, because AUTH_SYS was
   so suited to the Unix environment, making NFS administration so
   similar to local file system administration, its use remained
   predominant despite its obvious weaknesses from the security
   standpoint.

8.4.2.  Background for Existing AUTH_SYS in NFSv4

   When NFSv4 was first defined (in [RFC3530]), RPCSEC_GSS was added as
   a MANDATORY to implement means of authentication which was optional
   to use, presumably under the assumption that other optional-to-
   implement authentication flavors, such as AUTH_SYS would be used by
   some clients

   The continued use of AUTH_SYS is troubling and hard to explain if one
   is focused on network security, but the following possibilities are
   worthy of note:

   o  It might well have been felt that the problems with AUTH_SYS,
      although troubling, did not really apply to the most common use
      case for NFS, on local area networks.

   o  The familiarity of AUTH_SYS to Unix administrators, and general
      consistency with existing UNIX methods of system administration
      may have made it difficult to contemplate its abrupt removal in
      NFSv4.0, with the expectation that doing so might have
      substantially impeded NFSv4 adoption.





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   Regardless of why this happened, the important fact is that it did
   happen, despite the serious security problems that it gave rise to.
   Later subsections of Section 8.4 will discuss ways to address the
   resulting situation.

8.4.3.  Core Issue to Resolve for AUTH_SYS

   Given the serious security weaknesses described in Section 5.2, there
   is clearly a need to discourage its further use in its existing form,
   since the difficulties with it will not be eliminated by the adoption
   of encryption of NFSv4 connections alone

   There are two basic forms that such an effort might take:

   o  Seek to discourage the use of AUTH_SYS in the expectation that it
      will be eventually replaced by RPCSEC_GSS or a new security
      flavor.

   o  Seek to eliminate or mitigate its security problems and to
      discourage the use AUTH_SYS variants that have not addressed the
      underlying problem, in favor of a revised approach to AUTH_SYS
      with better security, based on client host authentication.

   While the author is strongly of the opinion that the second choice is
   more likely to be successful, and this document reflects that view,
   there is no intention to foreclose the first option, should the
   working group choose it.  If that option is chosen, then the material
   in Section 8.4.6 becomes irrelevant and can be ignored while much of
   that in Section 8.4.5 can be simply modified to expand its scope, as
   described below in that section.

8.4.4.  Need to Better Document and Explain Issues with AUTH_SYS

   As described in Section 8.1 there is a need for an appropriate threat
   analysis for NFSv4.  For a number of reasons, issues with AUTH_SYS
   that would make it difficult to refer to in an NFSv4-wide security
   document without some additional work preparatory work:

   o  Unlike the case of RPCSEC_GSS, there is no discussion of possible
      security threats.

   o  There is no complete documentation how AUTH_SYS is to be used.

   o  The reason for deciding that AUTH_SYS is "insecure", while
      probably valid, adds considerable confusion since it makes it
      harder to address the issue complained of.





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   Under other circumstances, it might have been possible to dispense
   with further analysis of AUTH_SYS because of the following facts:

   o  AUTH_SYS is declared "insecure", which might be considered as
      making a further security analysis beside the point.

   o  There are a number of statements with [RFC5531] limiting the use
      of AUTH_SYS, which might lead a reader to conclude that it was, in
      essence, a historical artifact.

   Despite the above, we will need a more complete of treatment of
   AUTH_SYS security for a number of reasons.

   o  Despite the recognition of its insecurity and restrictions on its
      use, AUTH_SYS has been at least on a par with RPCSEC_GSS in terms
      of NFSv4 use, for over a decade following.

   o  Given that the ongoing security issues with AUTH_SYS might give
      rise to efforts to address them, an accurate understanding of
      these issues is even more important, regardless of how the working
      group chooses to resolve the issue discussed in Section 8.4.3>.

      If the decision is made to improve the security characteristics of
      AUTH_SYS, it is important to understand existing security issues
      and how they might be best addressed.

      If the decision is made to eliminate the use of AUTH_SYS, an
      adequate understanding of the security issues that made that
      decision necessary would seem to be required.  In that context,
      the current statement in [RFC5531], regarding the insecurity of
      AUTH_SYS needs to be clarified.

   o  It is likely that attempts to eliminate or restrict use of
      AUTH_SYS will take the form of a recommendation that it not be
      used or only be used in certain ways or under certain
      circumstances.  Such recommendations normally require that the
      user be made aware of the consequences of doing something other
      than what is recommended.  In this case that would be either to
      use AUTH_SYS or to use it without client host authentication.

   An important question is where such a treatment should appear.  In
   deciding this question, the important question is whether, at this
   point, it is best addressed as a feature associated with NFSv4 or
   with RPC.

   o  While structurally, AUTH_SYS, presented as one of security
      supported security flavors associated with RPC would seem to
      require treatment within the framework of RPC, its recent



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      treatment raises questions about continuing to deal with it solely
      within this framework.  This is not due solely because of the
      attempt (in [RFC5531]) to discourage its use, as was done for
      AUTH_DH.  In that case it remains appropriate to discuss it as
      part of RPC, without a threat analysis, since there is no
      continuing use justifying another course.

   o  The continued use of AUTH_SYS by all NFSv4 minor versions might
      well be considered to justify a transfer of responsibility to
      NFSv4, with the authentication flavor being mentioned, in RPC
      specifications, only as a historical artifact.

      The potential continued use of AUTH_SYS with client-host
      authentication strengthens the NFSv4 connection.  Since
      [I-D.ietf-nfsv4-rpc-tls] assigns the specification of policies
      related to authentication to the ULP, it seems that AUTH_SYS needs
      to be discussed by NFSv4 documents in a manner more substantial
      than simply listed as another authentication flavor.

   o  AUTH_SYS, both with and without client host authentication could
      be discussed in its own document, including an appropriate threat
      analysis.

      That document could be referenced by a new document updating or
      obsoleting [RFC5531].  This would provide an opportunity to
      address existing text which was essentially ignored by NFSv4.

      That document could also be referenced by a new standards-track
      document dealing with NFSv4 security.  The threat analysis would
      provide a basis for the whatever approach the working group
      decides to take with regard to the discussion of AUTH_SYS with
      client-host authentication.  See Section 8.4.6 for further
      details.

   The last of these is most likely to be adopted regardless of how the
   working group decides the issue described in Section 8.4.3.  However,
   if the working group decides to strongly discourage the use of
   AUTH_SYS even with client-host authentication, the first is a
   possibility that should be considered.

8.4.5.  Issues to Address for Existing Use of AUTH_SYS

   This section presents material that might be included in a standards-
   track document in an effort to suitably discourage use of AUTH_SYS in
   its current (insecure) form.

   While it is sometimes the case that such a task can be accomplished
   by substituting one of the terms defined in [RFC2119] by another,



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   that is not the case here While the designation of AUTH_SYS as
   optional (to implement) with [RFC7530] and [RFC5661] using the
   language "MAY be implemented", is wrong and probably needs to be
   fixed, the situation is more complex than generally recognized.  It
   should be kept in mind that these terms are, in many cases, ignored
   or followed while ignoring the underlying intent.  As a result, such
   changes, without supporting explanations might not be effective in
   changing implementer behavior.

   To summarize the confusing situation with AUTH_SYS and NFS and the
   role of the RPC specification, [RFC5531].

   o  At the time of publication of [RFC5531], AUTH_SYS was extensively
      used by NFSv2 [RFC1094], NFSv3 [RFC1813], and NFSv2 [RFC1094],
      NFSv4.0 [RFC3530].

   o  The Security Considerations Section of states "AUTH_SYS SHOULD NOT
      be used for services that permit clients to modify data", which
      all versions of NFS clearly are.

   o  Section 10 of [RFC5531] states "Implementors MAY include AUTH_SYS
      in their implementations to support existing applications."
      Although this statement was probably intended to authorize
      continued use of AUTH_SYS, the contradiction between this
      statement and the Security Consideration section is not noted so
      there is no way to determine how this contradiction is to be
      resolved or precisely what "an application" is.

   o  The case of NFsv4.1, later defined in [RFC5661], is different
      since, being a separate protocol, with additional vulnerabilities
      when AUTH_SYS is used, it would presumably not be an "existing
      application".

   o  Turning from [RFC5531] to [RFC5661] and [RFC7530], we find
      AUTH_SYS described as an OPTIONAL means of authentication, with
      its security weaknesses not being discussed or treated as a
      significant concern.

   While there may well be sufficient loopholes within [RFC5531] to
   avoid an outright contradiction of the rules established there, it is
   certainly troubling that the security implications of implementing
   and using AUTH_SYS are not properly recommended against.

   While we may need to adjust the normative language, the effect of
   doing so is limited for reasons that have already been discussed.  As
   a result, we need to put substantial emphasis on clearly stating the
   consequences of doing what "SHOULD NOT" (or "should not") be done, as
   is suggested by [RFC2119], at least for the former case.



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   The following text is one way to present the situation:

      The use of AUTH_SYS, as described (incompletely) in Appendix A of
      [RFC5531] is quite detrimental to security and so SHOULD NOT be
      used.

      This is so because it involves accepting requests from clients on
      behalf of specific users without authentication of the clients
      themselves.  In essence, the task of authentication is delegated
      to NFSv4 client implementations, with the server accepting such
      authentication decisions.  Normally, such an arrangement would
      require the establishment of a trust relationship between client
      and server.

      Typically, when using AUTH_SYS, use of a privileged port
      represents the client kernel's judgment (by granting root access)
      that the client proper is to be trusted but there is no good
      reason to trust the client kernels in this regard.

      Although [RFC5661] and [RFC7530] previously treated implementation
      of AUTH_SYS as optional, it appears that this treatment was in
      error in that it focused on the relevant interoperability
      constraints without attention to the security consequences of use
      (discussed in Section 7 of [RFC2119]).  While use of AUTH_SYS was
      not characterized using any of the keywords defined in [RFC2119],
      it was reasonable for implementers to assume this was valid given
      the lack of attention to network security issues and the fact that
      there would be no point in implementing support for AUTH_SYS in
      servers if it could not be used.

      Although, as a result of these previous approaches to AUTH_SYS
      without client host authentication, it might be used extensively
      despite the security issues that cause us to specify that it
      "SHOULD NOT" be used are sufficient to justify this shift.
      However, due to the difficulty of making such a shift, the need to
      maintain continuity of support is a valid reason to continue to
      use it in this way, as long as this decision is made with
      awareness of the security consequences:

      *  That it is possible for an attacker to impersonate a trusted
         client by using its IP address in source IP address of packet
         sent, enabling to send its own requests to read or modify data,
         as any particular user.

      *  That compromising any client whose AUTH_SYS requests are
         accepted allows it to create a connection from which its
         unauthenticated requests will be executed by the server.




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      *  That it is possible for attackers to work around "root
         squashing" since it can assume any identity it intends to,
         other than that of root.

8.4.6.  Issues to Resolve for Revised Approach to AUTH_SYS

   The availability of client-host authentication makes possible a
   revised approach to AUTH_SYS addressing some of its security
   vulnerabilities.  A revised approach to AUTH_SYS might provide:

   1.  The ability to prevent, using client host-authentication, another
       machine masquerading as the expected client.

       The authentication features described in
       [I-D.ietf-nfsv4-rpc-tls], would be assure that you could identify
       trusted client machines, eliminating a major security issue with
       AUTH_SYS.  On the other hand, it is not clear whether servers
       would be wise to trust clients to this degree, especially if the
       items below (#2 and #3) are not satisfactorily dealt with.

   2.  It would be possible to include, as part of the client
       authentication material, information known only to the client and
       the server.  The secret value would be chosen by the client, and
       saved so it is usable by later client instances.  If this were
       done, it would prevent any process with root privileges on a
       trusted machine from impersonating the trusted client.  If this
       were not done, then any compromise of a single trusted client
       would compromise any server which trusted it to present AUTH_SYS
       requests.

       To make this approach viable, servers would have to maintain, in
       persistent storage, a record of the secret value assigned to each
       authenticated client.  When an authenticated client connected
       with a different value it would indicate that a root process on
       the client-host was attempting to impersonate the NFSv4 client.

   3.  The power granted to the authenticated client-host, to make a
       request on behalf of user or group has troubling consequences.
       Although most implementations have the ability to exclude
       requests from the root user, that may not, as has been noted
       previously, be sufficient to satisfactorily deal with the
       problem, since many deployments contain security-critical files
       that can be accessed and modified but users other than root.

       It would be desirable to exclude a wider range of users such as
       all users within a given group (or alternatively include only
       users within a given group).  However, neither of these is viable
       since servers receiving AUTH_SYS requests typically have no



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       knowledge of what users belong to what groups, relying on the
       AUTH_SYS client to provide this information within the request.

       Given this lack of knowledge on the part of the servers, any
       restrictions on the ability of AUTH_SYS requests to access or
       modify files designate a set of protected files in some way.
       Since designating a list of files is complicated and hard to
       maintain, it might be possible to describe the files whose access
       and/or modification by means of an ACL.  When a request is made
       to access a file, that request is suppressed (i.e. treated as a
       request by "nobody") iff it would be allowed to access by the
       designated ACL and similarly in the case of modifying requests.

   How to address the question of the potential use of AUTH_SYS with
   client-host authentication would depend on the working group's
   judgement about how likely such an arrangement would be likely to be
   in providing security when AUTH_SYS is used.  This in turn would
   depend on the working group's judgment as to whether solutions for #2
   and #3 could be defined and effectively deployed, as well as the
   results of the threat analysis

   I am assuming that AUTH_SYS with client-host authentication needs to
   be considered inferior to RPCSEC_GSS but sufficiently superior to
   AUTH_SYS without client authentication, to make it desirable to
   encourage its use, given that it is impossible to eliminate use of
   AUTH_SYS, even with a "MUST NOT".  A number of potential
   introductions to the topic, of varying tone are explored below:

   o  If the working group wants to focus on the improvement relative to
      AUTH_SYS without client-host authentication, the following
      paragraphs might be an appropriate introduction:

      When AUTH_SYS is used with client-host authentication, then the
      server, by allowing use of AUTH_SYS for that specific client, is
      essentially delegating the user authentication task to that client
      who is trusted by the server to perform that task locally, just as
      typically done when authenticating users for the purpose of local
      file access, even though the scope of damage that could be enabled
      by any false authentication is likely to be much wider in this
      case.

      By accepting AUTH_SYS requests from a particular client, a server
      is relying on the security of the client for the security of all
      data stored on the server.  This is in contrast to RPCSC_GSS, in
      which authentication is provided for each request issued.  Because
      of this, the use of AUTH_SYS should only be allowed from client
      hosts that can reasonably be trusted.




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   o  If the working group wants to adopt a more cautionary tone
      regarding use of AUTH_SYS with client-host authentication, the
      following paragraphs might be an appropriate introduction:

      By accepting AUTH_SYS requests from a particular client, a server
      is relying on the security of the client for the security of all
      data stored on the server.  This is in contrast to RPCSC_GSS, in
      which authentication is provided for each request issued.  Because
      of this, the use of AUTH_SYS should only be allowed from client
      hosts that can reasonably be trusted and whose internal security
      is sufficiently robust that the additional risk to server data can
      be considered reasonable.

   o  If the working group wants to focus more on encouraging use of
      RPCSEC_GSS, then on improving the security of those choosing to
      use AUTH_SYS, a paragraph like the following might be appropriate.

      While the use of AUTH_SYS with client-host authentication
      eliminates some of the major security issues that arise from use
      of AUTH_SYS, it is still inferior, from a security point of view,
      to RPCSEC_GSS.  As a result, its use should be limited to
      situations in which, use of RPCSEC_GSS is not a practical
      possibility.

   The following paragraph might be added if item #2 is not successfully
   addressed:

      It should be noted that any security weaknesses in the client host
      kernel which might allow an attacker to execute in privileged
      mode, are likely to allow that that attacker to present AUTH_SYS
      requests to the server and have them executed without any
      authentication beyond verifying that they were issued by a trusted
      host.

   The following paragraph might be added if item #2 is successfully
   addressed:

      In order to assure that it is not possible for a process running
      as root to successfully masquerade as a previously active kernel-
      based client on that machine, user-level clients even privileged
      ones, will present distinct authentication material from a kernel-
      based client and from each other.  Servers SHOULD maintain,
      persistently, sufficient information so to be able to detect a
      situation in which process with root privileges on a trusted
      server masquerades as a client previously recognized on that and
      judged secure.





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   The following paragraph might be added if item #3 is not successfully
   addressed:

      There is no standardized way the server can effectively limit the
      range of client user identities and group memberships assumed by
      AUTH_SYS requests except for the commonly implemented practice of
      "root squashing".

   The following paragraph might be added if item #3 is successfully
   addressed:

      Server SHOULD provide a means by which specific sets of sensitive
      files are made inaccessible or unmodifiable by use of AUTH_SYS
      requests, in order to limit the damage that could occur in the
      event that a client compromise allows unauthenticated requests to
      be generated and acted upon.  One desirable way of providing such
      a facility would be to allow an ACL to be associated with each
      authenticated client host (e.g. by designating a file whose ACL is
      to be used).  If this is done any request whose user together with
      a group set would allow it to be accepted by the specified ACL
      would be rejected.

   The following closing paragraphs are proposed for an eventual
   introduction to AUTH_SYS, as revised.  In these paragraphs, material
   to be added only if a particular item above is addressed or not
   addressed will appear in brackets with the prefix "if-#x:" or "if-
   not-#x:".

      The ability to make AUTH_SYS requests of a server SHOULD be
      limited to those cases in which the client host making those
      requests can be trusted to appropriately verify a user's
      credentials (e.g. passwords) before issuing RPC requests on that
      user's behalf. [if-#3: This limitation should be applied even when
      the set of users or owning groups is restricted to specially
      protect files deemed sensitive.] [if-not-#3: When not so limited,
      requests purportedly from any user except possibly root, can be
      synthesized and acted upon, without effective authentication.]

      For that reason, accepting AUTH_SYS requests from a large set of
      client hosts is a practice to be avoided, with individual hosts
      included where their security has been verified.  The only
      possible exception is where a set of policies is in place which
      effectively limits the kernel software allowed to run on those
      hosts to ensure that those hosts appropriately providing user
      authentication [if-not-#2: and capable of excluding untrusted code
      from masquerading as an NFSv4 server by assuming root privileges.]





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8.5.  Handling of State Protection

8.5.1.  Background

   The inclusion of state management within NFSv4 created new security
   issues in which the objects requiring protection were not files
   associated with particular users but locks, opens, and delegations,
   associated with particular clients.

   In NFSv4.0, some protection could be provided when RPCSEC_GSS was
   used by limiting modification of state objects to users having access
   to the associated file.  Nevertheless, the fundamental issue remained
   unresolved.

   When sessions were introduced into NFSv4 (in NFSv4.1) there were
   additional vulnerabilities that needed to be protected against.
   There needed to be protection to prevent a session established by one
   client being bound to a connection established by another client,
   leading to the following possibilities:

   o  The existing session could be destroyed.

   o  The associated clientid could be destroyed.

   o  The existing session slots could be used resulting in the
      legitimate owner of the session having his requests rejected
      because his slot sequence values had been rendered invalid because
      of the interloper's requests using the same slots.

   Facilities were defined in [RFC5661] to allow such client-based
   protection to be implemented: SP4_MACHCRED and SP4_SSV but
   implementation has been quite limited.  Client-host authentication
   makes it possible to apply such protection more generally, as
   described below.

8.5.2.  Issues to be Addressed

   While transport-level encryption would make it harder for attackers
   to mount attacks based on these vulnerabilities, the authentication
   material provided when a TLS connection is established could enable
   the vulnerabilities discussed above to be eliminated without the work
   of implementing SP4_MACHCRED or SP4_SSV, and irrespective of whether
   the client is using AUTH_SYS or RPCSEC_GSS.

   If one has a TLS connection including suitable authentication
   material, then the server is in a position to reject attempts to bind
   to sessions established under this connection by other connections
   that are not TLS connections or are not established by the same



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   client, unless SP4_MACHCRED or SP4_SSV is in effect.  This would make
   state protection available to those using SP4_NONE, i.e. the vast
   majority, whether they used RPCSEC_GSS or AUTH_SYS with client-host
   authentication.

   The fact that this is an NFSv4.1-only security feature make it
   difficult to fully it address solely in the NFSv4-wide security
   document which we writing.  The following plan is intended to allow
   the security document to be published before proceeding to publish
   the anticipated rfc5661bis:

   o  In the anticipated standards-track NFSv4 security document, it can
      be stated that when SP4_NONE is specified and the client owning
      the session is authenticated, then the session is protected from
      being bound-to or destroyed by an unauthenticated client or a
      different authenticated client, then effect is the same as if
      SP4_MACHCRED or SP4_SSV were used by the owning client and a non-
      matching client was found.  Since the new standards-track document
      will update [RFC5661], that provides adequate notice of this
      change

   o  Later, when rfc5661bis is ready to be published, there would
      opportunity to provide introductory material explaining the
      various ways clients can be authenticated for the purpose of state
      protection, including use of SP4-MCHCRED, SP4_SSV and
      authentication of part of use of RPC-TLS and defining the
      circumstances under which one connection can access/modify state
      owned by an authenticated client.  References to abstract
      relationships would replace most current mentions of SP4_NONE,
      SP4_MCHCRED, and SP4_SSV in [RFC5661].

   It should be noted that this use of client-host authentication
   provides applicable protection even when AUTH_SYS is used.  This is
   so however the issues discussed in Section 8.4.6 are addressed, and
   independent of the decision made regarding the choice discussed in
   Section 8.4.3 unless it is decided that AUTH_SYS MUST NOT be used.
   Issues regarding the impersonation of a large set of users are not
   relevant because user ids are not referenced.  Furthermore, the
   possibility of a privileged user-level client implementing a denial-
   of-service attach (if issue #2 in Section 8.4.6 is not addressed), is
   not of concern since such a privileged process would find it far
   easier to deny service directly on the client host.

9.  Steps Going Forward

   This document is expected to facilitate concrete discussion of how to
   address security in NFSv4.  It is expected to be modified to reflect
   working group comments.  If the working group is amenable to this



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   approach, at some point a request will be made to adopt it as a
   working group item.

   A large part of the discussion is expected to concern how AUTH_SYS
   will be dealt with.  However, it is not expected that the working
   group needs to reach consensus on this issue immediately.  This
   document could be adopted as a working group item if it is an
   appropriate vehicle to organize the discussion of related issues,
   such as formulating a consensus regarding the treatment of AUTH_SYS.

   It is anticipated that, once the document is adopted as a working
   group item, this document will be used to discuss the writing of
   multiple standards-track documents, which may need co-ordination
   since they address a set of related issues:

   o  A new standards-track document discussing security for all NFSv4,
      updating [RFC7530] and [RFC5661].  It is intended that this
      document be referred to by rfc5661bis when it is ready for
      publication but it should be able to be published, on its own
      before that, since it would update [RFC5661].

   o  A new standards-track document discussing AUTH_SYS, including
      discussion of the potential use of client-host authentication.

   o  A new standards-track document updating [RFC5531].

   This document is being written to guide the working group in
   preparing future standards-track documents.  There are no plans to
   publish it as an RFC.  If a milestone is to be associated with it,
   the appropriate goal would be completion of WGLC.

10.  IANA Considerations

   The current document does not require any actions by IANA.

11.  Security Considerations

   The convention of requiring a Security Considerations Section within
   an I-D encounters difficulties when applied to a document dealing
   solely with security, making it most unclear what such a section
   might contain for such documents.

   In addition, the nature of this particular document poses further
   issues regarding the possible content of a Security Consideration
   Section:






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   o  This document does not define a protocol or protocol feature that
      can be implemented, making it unclear how a threat analysis could
      be performed whose security considerations would be described.

   o  Despite this document's informational nature, it does attempt to
      address security issues for an existing set of protocols

   In light of the above, this section will summarize the security-
   related message of earlier sections and will, in subsections, discuss
   the appropriate contents of Security Considerations Sections for a
   eventual standards-track documents to be written

   The message of this document with regard to security issues can be
   summarized as follows

   o  The current security approach for the NFSv4 protocols has some
      significant weaknesses, requiring a major reworking of the
      security approach.

   o  This reworking can be accomplished without change to the NFS
      protocols per se, by taking advantage of recent security
      improvements defined within the RPC layer.

   o  A threat analysis, not provided in previous NFSv4 specification
      documents, will be the provided within a new standards-track
      document addressing security for all minor versions of NFSv4.

   o  Because there is no threat analysis of AUTH_SYS in existence, one
      needs to be provided, preferably in a new standard-track document
      dealing with AUTH_SYS.  This is despite the designation of
      AUTH_SYS (in [RFC5531] as "insecure", which was never, at least in
      the case of NFSv4, acted upon.  Such a document is needed to
      clarify the security weaknesses of AUTH_SYS and the degree such
      weakness could be rectified by the implementation of TLS-based
      encryption and/or client host authentication.

11.1.  Security Considerations Section for Eventual NFSv4-wide
       Standards-track Security Document

   Although it is clear that such a document would need to include a
   threat analysis, as provided for by RFC3552/BCP72 [RFC3552].
   However, the length of such an analysis might well be so large that
   it cannot be reasonably contained within a Security Considerations
   Section.  In that case, the Security Considerations Section will
   summarize the results of the threat analysis, referring to those
   parts that appear in other sections of the document.





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11.2.  Security Considerations Section for Revised RPC Specification
       Document

   The general form of this section in [RFC5531] in which references are
   made to documents for each security flavor, seem appropriate.
   However, the following changes are likely to be required:

   o  The treatment of AUTH_SYS needs to reference the new document
      describing AUTH_SYS, rather than the incomplete description in
      Appendix A, which needs to be removed.

      In addition, the last two sentences of the initial paragraph of
      section 14 need to be reworked to respond to the fact that while,
      there was no clear violation of them, this insecure authentication
      flavor was used by NFSv4 for over a decade subsequently.  Although
      the following attempt at loophole removal might not survive the
      editing and review process, the issues it raises are worth
      considering.

         As discussed in the referenced document, the use of AUTH_SYS in
         the clear without client host-authentication introduces
         significant security vulnerabilities in that it allows
         unauthenticated requests to be created by an unauthenticated
         client.  This make its use highly inappropriate for any RPC
         service, particularly those that allow clients to modify data.

         Similarly, in specifications of Standards track RPC services,
         it is inappropriate to make such use REQUIRED or RECOMMENDED.
         Where such use is allowed at all (whether by "MAY" or "SHOULD
         NOT" is used), viable non-disruptive alternatives need to
         provided and the associated Security Consideration sections
         need to clearly explain the security consequences of use.

   o  The case of AUTH_DH is similar to that of AUTH_SYS in that there
      is a simple declaration of insecurity.  However, there is a
      document referenced and there is no indication that the loopholes
      in the treatment were bypassed in this case, as they were for
      AUTH_SYS.  Still, it might worth revising the final two sentences
      as were done with AUTH_SYS.

   o  Given that the final paragraph of the Security Considerations
      section was drafted without consideration of reverse direction
      operation and without consideration the possibility that either
      TLs encryption or client host authentication might be available
      (and potentially REQUIRED), redrafting it to be more appropriate
      for the environment made possible by [I-D.ietf-nfsv4-rpc-tls] is
      likely.




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      The following replacement text is suggested to deal with these
      issues:

         Standards Track RPC services need to mandate server and client
         support for RPCSEC_GSS when used in the forward direction.  The
         treatment of authentication for reverse-direction operation
         needs provide for authentication of the identity of the
         requester (i.e. on the server) to the responder (i.e. on the
         client).  When reverse direction requests are not made on
         behalf of a specific user, the mutual authentication provided
         by RPC-TLS can be relied on but authentication of users on
         reverse-direction will need to use RPCSEC_GSS.

         For either direction of operation, when user identities must be
         authenticated, such services need to mandate support for an
         authentication pseudo-flavor.  In situation in which it is
         possible/allowed for RPC services to be used without TLS
         encryption there is also a need to mandate pseudo-flavors with
         additional appropriate levels of security, depending on the
         need for authentication only, integrity (a.k.a.  non-
         repudiation), or encryption to provide data confidentiality.

11.3.  Security Considerations Section for Standard-track Document
       dealing with AUTH_SYS

   As mentioned above, a prime goal of the threat analysis for AUTH_SYS
   would be to clarify the degree to which the security weaknesses of
   AUTH_SYS can be successfully addressed using transport-level security
   facilities.  Those pieces of the threat analysis might well appear
   outside the Security Consideration section proper.

   The Security Considerations needs to summarize these and provide a
   basis for ULPs that allow AUTH_SYS to specify the appropriate
   conditions for use and the consequences of not enforcing these.

12.  References

12.1.  Normative References

   [I-D.ietf-nfsv4-rpc-tls]
              Myklebust, T. and C. Lever, "Towards Remote Procedure Call
              Encryption By Default", draft-ietf-nfsv4-rpc-tls-07 (work
              in progress), April 2020.

   [I-D.ietf-nfsv4-rpcrdma-version-two]
              Lever, C. and D. Noveck, "RPC-over-RDMA Version 2
              Protocol", draft-ietf-nfsv4-rpcrdma-version-two-01 (work
              in progress), January 2020.



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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC3552]  Rescorla, E. and B. Korver, "Guidelines for Writing RFC
              Text on Security Considerations", BCP 72, RFC 3552,
              DOI 10.17487/RFC3552, July 2003,
              <https://www.rfc-editor.org/info/rfc3552>.

   [RFC5531]  Thurlow, R., "RPC: Remote Procedure Call Protocol
              Specification Version 2", RFC 5531, DOI 10.17487/RFC5531,
              May 2009, <https://www.rfc-editor.org/info/rfc5531>.

   [RFC5661]  Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed.,
              "Network File System (NFS) Version 4 Minor Version 1
              Protocol", RFC 5661, DOI 10.17487/RFC5661, January 2010,
              <https://www.rfc-editor.org/info/rfc5661>.

   [RFC7530]  Haynes, T., Ed. and D. Noveck, Ed., "Network File System
              (NFS) Version 4 Protocol", RFC 7530, DOI 10.17487/RFC7530,
              March 2015, <https://www.rfc-editor.org/info/rfc7530>.

   [RFC7862]  Haynes, T., "Network File System (NFS) Version 4 Minor
              Version 2 Protocol", RFC 7862, DOI 10.17487/RFC7862,
              November 2016, <https://www.rfc-editor.org/info/rfc7862>.

   [RFC8166]  Lever, C., Ed., Simpson, W., and T. Talpey, "Remote Direct
              Memory Access Transport for Remote Procedure Call Version
              1", RFC 8166, DOI 10.17487/RFC8166, June 2017,
              <https://www.rfc-editor.org/info/rfc8166>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

12.2.  Informative References

   [RFC1094]  Nowicki, B., "NFS: Network File System Protocol
              specification", RFC 1094, DOI 10.17487/RFC1094, March
              1989, <https://www.rfc-editor.org/info/rfc1094>.

   [RFC1813]  Callaghan, B., Pawlowski, B., and P. Staubach, "NFS
              Version 3 Protocol Specification", RFC 1813,
              DOI 10.17487/RFC1813, June 1995,
              <https://www.rfc-editor.org/info/rfc1813>.





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   [RFC3530]  Shepler, S., Callaghan, B., Robinson, D., Thurlow, R.,
              Beame, C., Eisler, M., and D. Noveck, "Network File System
              (NFS) version 4 Protocol", RFC 3530, DOI 10.17487/RFC3530,
              April 2003, <https://www.rfc-editor.org/info/rfc3530>.

   [RFC8178]  Noveck, D., "Rules for NFSv4 Extensions and Minor
              Versions", RFC 8178, DOI 10.17487/RFC8178, July 2017,
              <https://www.rfc-editor.org/info/rfc8178>.

Appendix A.  Acknowledgements

   The author would like to thank Chuck Lever (of Oracle) and Trond
   Myklebust (of Hammerspace) for their important work providing
   security at the RPC layer, enabling us to break the NFSv4 security
   logjam.

   The author would like to thank Tom Haynes (of Hammerspace) for
   introducing the idea of dealing with security for all minor versions
   in a single document.

Author's Address

   David Noveck
   NetApp
   1601 Trapelo Road
   Waltham, MA  02451
   United States of America

   Phone: +1 781 572 8038
   Email: davenoveck@gmail.com





















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