Re: [tor-dev] Support for full DNS resolution and DNSSEC validation

[Alexander Færøy <ahf@xxxxxxxxxxxxxx>]

Hello Christian,

On 2020/04/26 19:37, Christian Hofer wrote:
> I have a proposal regarding DNS name resolution.
> 
> Ticket: https://trac.torproject.org/projects/tor/ticket/34004
> Proposal: 
> https://trac.torproject.org/projects/tor/attachment/ticket/34004/317-secure-dns-name-resolution.txt
> Implementation: https://github.com/torproject/tor/pull/1869
> 
> All functioniality is behind the DNSResolver feature flag, so don't
> forget to activate it before you start testing.
> 
> Please let me know what you think.

Thanks for doing this work. I think our DNS subsystem has been lacking
behind for a while. This work is exciting.

Generally, after having done one pass over your code, I think the source
code is good quality, especially if this is your first contribution to
Tor! However, I think this is going to be a bit problematic for us to
import.

It will be hard, if not impossible, for Tor's Network Team to adopt 27k
LOC's in one pull-request. We will have to have multiple people going
over each line repeatedly and try to build up some confidence in this
code. If we are to go down this path, with having a complete DNS
subsystem in Tor, we need to add some capacity from our side to take
this in and maintain it. I think that with the recent layoffs in Tor, it
will be hard to achieve in a time-frame that is fair towards you.

One of the goals with our specification process is to have a set of
documents, which allows other people to understand how Tor is working to
the point where they should be able to implement Tor from scratch if
they found that useful. This isn't always possible today, but this is a
goal we should have in mind. Your proposal is mostly a specification of
the *implementation* of the DNS resolver patches and doesn't contain any
information on any changes to the network layer of Tor. Instead, those
seem to be referenced as the various DNS related RFCs from the IETF.
Configuration options of the Tor binary is largely an implementation
detail.

I wonder if it would make more sense to have an onion-aware
DNSSEC-enabled resolver *outside* of the Tor binary and have a way for
Tor to query an external tool for DNS lookups. Such tool should be
allowed to use Tor itself for transport of the actual queries. One of
the best parts of Tor (in my opinion) is the Pluggable Transport
subsystem. This subsystem allows external developers, researchers, and
hackers to build new technology that benefits users in censored areas
*without* having to alter a single line of C code in tor.git.

Let's say we had a "Pluggable DNS" layer in Tor. Users would be able to
configure their Tor process to *never* use the built-in DNS subsystem in
Tor, but instead outsource it to an external process that Tor spawns on
startup. This process could use .onion's to reach a
DNS-over-(TLS|HTTPS|TCP) server as onions themselves aren't looked up
via DNS.

A "Pluggable DNS" subsystem would be much less code, I believe, and it
wouldn't require us to have a DNS+DNSSEC implementation in the heart of
Tor to maintain in the future. Such a system would be similar to the
proposed design for Name => Onion lookups defined in proposal #279 by
asn, yawning, and dgoulet.

Lastly, I assume it's just for testing purpose, but I don't think we
could ship with CloudFlare's DNS-over-Onion services as the default
servers for a feature like this without having a discussion in the
community about it first :-)

All the best,
Alex.

-- 
Alexander Færøy
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