[Dnsmasq-discuss] Uppercase queries are forwarded differently depending on the protocol (tcp vs udp)

[Dmitry Pasiukevich]

Hi,

Good news is that on git HEAD there's no such bug! 🎉

But it's reproducible on dnsmasq 2.86
https://thekelleys.org.uk/dnsmasq/dnsmasq-2.86.tar.gz
Maybe it would be useful if you'd like to trace the cause/fix.

/usr/local/sbin/dnsmasq -k --log-facility=- --server=/com/8.8.8.8
--log-queries=extra --log-debug --port=10054 --cache-size=0

1. dig +short -p 10054 example.com
dnsmasq[1479386]: 1 127.0.0.1/54512 query[A] example.com from 127.0.0.1
dnsmasq[1479386]: 1 127.0.0.1/54512 forwarded example.com to 8.8.8.8

2. dig +short +tcp -p 10054 example.com
dnsmasq[1482914]: 3 127.0.0.1/35851 query[A] example.com from 127.0.0.1
dnsmasq[1482914]: 3 127.0.0.1/35851 forwarded example.com to 8.8.8.8

3. dig +short +tcp -p 10054 example.COM
dnsmasq[1484740]: 103 127.0.0.1/35249 query[A] example.COM from 127.0.0.1
dnsmasq[1484740]: 103 127.0.0.1/35249 forwarded example.COM to 127.0.0.1

On Thu, Sep 15, 2022 at 10:59 AM Simon Kelley <simon at thekelleys.org.uk>
wrote:

>
>
> On 14/09/2022 22:32, Dmitry Pasiukevich via Dnsmasq-discuss wrote:
> > Hi,
> >
> > TLDR: DNS request to dnsmasq with upper-case domain is handled
> > differently if request is sent over TCP vs UDP
> >
> > I run a server to forward "cluster.local" queries to another process:
> >
> /usr/sbin/dnsmasq-k--cache-size=1000--no-negcache--dns-forward-max=1500--log-facility=---server=/cluster.local/
> 127.0.0.1#10053--log-queries=extra--log-debug
> > <http://127.0.0.1/#10053--log-queries=extra--log-debug>
> >
> > dnsmasq 2.86 with IP 10.64.0.7
> >
> > 1. When I run:
> > dig +tcp kubernetes.default.svc.cluster.LOCAL @10.64.0.7 <
> http://10.64.0.7/>
> >
> > I get NOERROR but no data in the response. dnsmasq logs:
> > I0913 06:15:04.790606       1 nanny.go:146] dnsmasq[86]: 44065
> > 10.64.1.4/33015 <http://10.64.1.4/33015> query[A]
> > kubernetes.default.svc.CLUSTER.LOCAL from 10.64.1.4
> > I0913 06:15:04.851065       1 nanny.go:146] dnsmasq[86]: 44065
> > 10.64.1.4/33015 <http://10.64.1.4/33015> forwarded
> > kubernetes.default.svc.CLUSTER.LOCAL to 169.254.169.254
> >
> > As you can see dnsmasq doesn't modify the domain. Because it's a
> > "CLUSTER.LOCAL" and not a "cluster.local" it's forwarded to the server
> > 169.254.169.254 set in the /etc/resolv.conf. And not the
> > --server=/cluster.local/127.0.0.1#10053 <http://127.0.0.1/#10053>
> >
> > 2. When I run exactly the same query but over UDP not TCP:
> > dig kubernetes.default.svc.CLUSTER.LOCAL @10.64.0.7 <http://10.64.0.7/>
> >
> > I get NOERROR and correct response:
> > kubernetes.default.svc.CLUSTER.LOCAL. 30 IN A   10.68.0.1
> >
> > dnsmasq logs in this case:
> > I0913 06:19:20.820425       1 nanny.go:146] dnsmasq[11]: 44471
> > 10.64.1.4/49622 <http://10.64.1.4/49622> query[A]
> > kubernetes.default.svc.CLUSTER.LOCAL from 10.64.1.4
> > I0913 06:19:20.820866       1 nanny.go:146] dnsmasq[11]: 44471
> > 10.64.1.4/49622 <http://10.64.1.4/49622> forwarded
> > kubernetes.default.svc.cluster.local to 127.0.0.1
> >
> > In this case the domain in the query is changed to the lower-case and it
> > matches "cluster.local" and forwards to 127.0.0.1 as expected.
> >
> > 3. When I run exactly the same query over TCP but fully lower-case it
> > works as well.
> >
> > Is this a bug or intended behaviour or maybe I misunderstood the logs?
> > Thanks!
> >
>
> Definitely not intended behaviour.
>
> Also not immediately reproducible in the current development code,
> though I don't recall fixing anything that might cause this. Would it be
> easy for you to repeat the tests using the git HEAD branch for a quick
> win? If that fails for you I'll try harder to reproduce the problem.
>
>
> Cheers,
>
> Simon.
>
> > _______________________________________________
> > Dnsmasq-discuss mailing list
> > Dnsmasq-discuss at lists.thekelleys.org.uk
> > https://lists.thekelleys.org.uk/cgi-bin/mailman/listinfo/dnsmasq-discuss
>
> _______________________________________________
> Dnsmasq-discuss mailing list
> Dnsmasq-discuss at lists.thekelleys.org.uk
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>


-- 
Dmitry Pasiukevich
Software Engineer
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