Re: [DNSOP] Incompatibility with indicating client support for EDE (draft-ietf-dnsop-structured-dns-error)

On Wed, 24 May 2023 at 01:48, Tommy Pauly <tpauly=40apple.com@dmarc.ietf.org>
wrote:

> Using length=2 and INFO-CODE=0 sounds fine to me.
>
> For the dependency on draft-ietf-add-resolver-info, I don't think we need
> to impose that dependency. I'd much prefer to allow clients to look at that
> optionally, but still be able to include the hint and use the extra text if
> it parses correctly.
>

Dependency on draft-ietf-add-resolver-info was added to address the threat
where an attacker might inject (or modify) the EDE EXTRA-TEXT field with an
DNS proxy or DNS forwarder that is unaware of EDE.More details are
discussed in Section 10 of the draft.

Cheers,
-Tiru

>
> Tommy
>
> On May 23, 2023, at 9:52 AM, Dan Wing <danwing@gmail.com> wrote:
>
> EDE length=2 with INFO-CODE=0 works nicely.
>
> Also because non-EDE-aware DNS responders can be vulnerable to attacks
> described in Security Considerations, the Security Considerations section
> currently suggests clients use draft-ietf-add-resolver-info to check if
> server supports EDE. This needs better clarification in the document that
> client has to check draft-ietf-add-resolver-info before including EDE OPT
> in its DNS query. This check will further help interop by only sending EDE
> in requests to servers that indicated support via
> draft-ietf-add-resolver-info. However, it creates
> draft-ietf-add-resolver-info as another hurdle to deployment of Structured
> DNS error.  Thoughts?
>
> (I also put the above text into our github issues; I don't know which
> folks prefer.
> https://github.com/ietf-wg-dnsop/draft-ietf-dnsop-structured-dns-error/issues/26
> )
>
> -d
>
>
> On May 22, 2023, at 7:44 PM, Tommy Pauly <tpauly=
> 40apple.com@dmarc.ietf.org> wrote:
>
> Thanks, Mark.
>
> For what it's worth, I just ran two other tests, and for both of these
> cases, all of the resolvers I tried did accept the request:
> - Choose a new EDNS option code point (I just tested 50, randomly)
> - Use EDE but set the length to 2 and the error to 0 (other error), rather
> than a length of 0
>
> Both of these seem viable, and I’ll let the authors and WG decide which is
> the right way forward.
>
> Best,
> Tommy
>
> On May 22, 2023, at 5:00 PM, Mark Andrews <marka@isc.org> wrote:
>
>
>
> On 23 May 2023, at 02:20, Tommy Pauly <tpauly=40apple.com@dmarc.ietf.org>
> wrote:
>
> Hello DNSOP,
>
> In draft-ietf-dnsop-structured-dns-error, there’s a description of how
> clients should indicate that they understand extended DNS errors (EDE) by
> sending an empty EDE option.
>
>
> https://www.ietf.org/archive/id/draft-ietf-dnsop-structured-dns-error-02.html#name-client-generating-request
>
> This is something that makes a lot of sense to me, and provides a great
> way to indicate that a client would prefer to receive proper
> blocked/filtered errors (with possible extra text) as opposed to a forged
> answer.
>
> However, in testing this out, I’m seeing inconsistent compatibility with
> some public resolvers. I was testing enabling this for encrypted resolvers
> only, and I see the following behavior for a sampling of resolvers using
> DoH:
>
> 1.1.1.1 - NOERROR, works fine!
> 9.9.9.9 - NOERROR, works fine!
> 8.8.8.8 - FORMERR on all responses
> dns.adguard-dns.com - SERVFAIL on all responses
>
> Do we think that this should be allowed in queries (and thus this is a bug
> in resolvers like 8.8.8.8 or AdGuard)? Or is there a problem with the
> approach this document is suggesting?
>
>
> RFC 8914 left whether EDE in requests was permitted or not undefined.  I
> can see an EDE implementation making the option parser return FORMERR if
> the EDE option length was less than 2 and applying that to both requests
> and responses.  RFC 8914 really should have said that EDE in requests
> should be ignored and then there would have been a possibility on extending
> behaviour based on adding EDE to a request.  We are already 10 years into
> trying to fix unknown EDNS option behaviour and are still getting FORMERR
> on unknown EDNS options in requests.  If the working group want to allow
> extending EDE by adding it to a request is should obsolete RFC 8914 now
> with RFC8914bis that specifies that EDE in requests are to be ignored.
>
> At the moment draft-ietf-dnsop-structured-dns-error-02 really should use
> another EDNS option code point.  It really is not backwards compatible with
> EDE the way it is currently specified.
>
>
> Best,
> Tommy
> _______________________________________________
> DNSOP mailing list
> DNSOP@ietf.org
> https://www.ietf.org/mailman/listinfo/dnsop
>
>
> --
> Mark Andrews, ISC
> 1 Seymour St., Dundas Valley, NSW 2117, Australia
> PHONE: +61 2 9871 4742              INTERNET: marka@isc.org
>
> _______________________________________________
> DNSOP mailing list
> DNSOP@ietf.org
> https://www.ietf.org/mailman/listinfo/dnsop
>
>
> _______________________________________________
> DNSOP mailing list
> DNSOP@ietf.org
> https://www.ietf.org/mailman/listinfo/dnsop
>
>
> _______________________________________________
> DNSOP mailing list
> DNSOP@ietf.org
> https://www.ietf.org/mailman/listinfo/dnsop
>
>
> _______________________________________________
> DNSOP mailing list
> DNSOP@ietf.org
> https://www.ietf.org/mailman/listinfo/dnsop
>