musl - Re: getaddrinfo() fails for domains with no AAAA records (regression?)

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Message-ID: <CAMhVC3YtPgVhU46L1VnT9zOyxQTkuFQAA5CV=f9s=uryKROyhQ@mail.gmail.com>
Date: Fri, 23 Jul 2021 23:25:36 +0300
From: Yuri Kanivetsky <yuri.kanivetsky@...il.com>
To: musl@...ts.openwall.com
Cc: "Olivier A." <olivier.antoine@...il.com>
Subject: Re: getaddrinfo() fails for domains with no AAAA records (regression?)

Can you possibly provide some quotes from the RFCs? The closest I could find is:

>      QNAME=host3.example. QTYPE=A, QCLASS=IN
>           the answer will reflect "no error, but no data"
>           because there is no A RR set at '*.example.'

https://datatracker.ietf.org/doc/html/rfc4592

And it's from an example.

Also, all other software I could get my hands on (basically, glibc, I
guess) ignores NXDOMAIN for AAAA RRs.

On Tue, Jul 20, 2021 at 12:12 AM Rich Felker <dalias@...c.org> wrote:
>
> On Mon, Jul 19, 2021 at 11:07:21PM +0200, Olivier A. wrote:
> > On 19/07/2021 14:58, Yuri Kanivetsky wrote:
> > >  [..]
> >
> > Hi,
> >
> > I notice that too. If both A and AAAA are sent and there is a
> > response for A and NXDomain for AAAA
> >
> > musl-libc discard both results. It's the expected behaviour
> > according to this commit:
> >
> > https://git.musl-libc.org/cgit/musl/commit/src/network/lookup_name.c?id=5cf1ac2443ad0dba263559a3fe043d929e0e5c4c
> >
> > And it conform to https://datatracker.ietf.org/doc/html/rfc8020
> >
> > It's was not the case before Alpine-Linux 3.13
> >
> > But I also notice that if the DNS reply ServFailed instead of
> > NXDomain for AAAA request, musl-libc retry 10 times, return 'bad
> > address' and do not fallback to return a A record.
> >
> > According to
> > https://datatracker.ietf.org/doc/html/rfc4074#section-4.3 it's not
> > expected.
>
> This behavior is necessary/mandatory to provide secure behavior under
> DNSSEC. Otherwise a forged response (causing ServFail) would result in
> a false answer returned to the application, indicating that only one
> or the other exists, rather than the correct inconclusive answer.
>
> This is https://sourceware.org/bugzilla/show_bug.cgi?id=27929

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