[Dnsmasq-discuss] [PATCH] Make ECC-GOST optional only

[Simon Kelley]

On 10/11/2022 17:02, Petr Menšík wrote:
> Hi!
> 
> I were testing my builds on rootcanary.org test, where dnsmasq is the 
> only one failing with DNSSEC validation enabled. I am not sure why, I 
> think gost crypto algorithm might be broken intentionally on Fedora or 
> RHEL for legal reason. But I have tested it on Debian unstable and the 
> result were same. It passes other algorithms, but fails on this one.
> 
> I have therefore made it possible to skip GOST support. In addition it 
> makes that default as well. Is there any distribution, which has GOST 
> support working? Is it possible that rootcanary.org has wrong signatures?
> 
> All other implementations return already insecure status - not 
> implemented algorithm. This change makes the same for dnsmasq.
> 
> Opinions on that?
> 


This sent me down something of a rabbit hole.

I've found and fixed multiple issues.

1) The code relies on algo_digest_name() returning NULL for any 
signature algorithm that's not supported, but the combination of a bug 
in the #defines in that code and a bug in libnettle made that not always 
true, so the DNSSEC code tried to validate things it shouldn't and 
failed,resulting in a SERVFAIL.

https://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=commit;h=f52cfdd8c37e09d77abdc151a4ddcf94f49f4821

fixes that.


2) The code to handle the GOST algorithms was broken; it used the wrong 
digest parameters and got the byte-order of the keys wrong and the order 
of the fields in the signature wrong. libnettle needs to be version 3.6 
or later to support the correct digest and signature algo.

https://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=commit;h=1f9215f5f92c5478c8aaba8054d192a5e6280e95


fixes.

3) The handling of unsupported hash algorithms in DS records was wrong. 
A correctly signed DS RRset which contains only unsupported hashes 
should be treated the same as a signed empty DS RRset and allow answers 
for the domain it covers to be returned unvalidated, and not to generate 
SERVFAIL responses.

https://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=commit;h=9ed3ee67ecd2388d319bff116b27bcc62286ccc

Fixes that.

With those three patches, rootcanary.org gives sensible results, both 
with dnsmasq compiled against Nettle-3.5 (which doesn't support ED488 
and GOST) and complied against Nettle-3.8, which does support both 
those. In the nettle-3.8 case records signed with RSA-MD5, DSA and 
DSA-NSEC-SHA1 are returned without being verified as specified in the 
DNSSEC Validation column of RFC 8624 para 3.1 The GOST signature and DS 
hash algorithms are still marked as MAY in that column, so I think it's 
fine to leave them in.


Given the above, I don't think there's a need to be able to disable the 
GOST algorithms, but I'm happy to hear arguments to the contrary.


Cheers,

Simon.

> Cheers,
> Petr
> 
> 
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