Subject: Re: [PATCH net 1/4] netfilter: remove nf_conntrack_helper sysctl and modparam toggles

From: Florian Westphal <[email-masked]>
Date: Fri, 2 Sep 2022 07:39:28 +0200

Jakub Kicinski <[email-masked]> wrote:
> On Thu,  1 Sep 2022 09:12:35 +0200 Florian Westphal wrote:
> > From: Pablo Neira Ayuso <[email-masked]>
> > 
> > __nf_ct_try_assign_helper() remains in place but it now requires a
> > template to configure the helper.
> > 
> > A toggle to disable automatic helper assignment was added by:
> > 
> >   a9006892643a ("netfilter: nf_ct_helper: allow to disable automatic helper assignment")
> > 
> > in 2012 to address the issues described in "Secure use of iptables and
> > connection tracking helpers". Automatic conntrack helper assignment was
> > disabled by:
> > 
> >   3bb398d925ec ("netfilter: nf_ct_helper: disable automatic helper assignment")
> > 
> > back in 2016.
> > 
> > This patch removes the sysctl and modparam toggles, users now have to
> > rely on explicit conntrack helper configuration via ruleset.
> > 
> > Update tools/testing/selftests/netfilter/nft_conntrack_helper.sh to
> > check that auto-assignment does not happen anymore.
> 
> From the description itself it's unclear why this is a part of a net PR.
> Could you elucidate?

Yes, there is improper checking in the irc dcc helper, its possible to
trigger the 'please do dynamic port forward' from outside by embedding
a 'DCC' in a PING request; if the client echos that back a expectation/
port forward gets added.

A fix for this will come in the next net PR, however, one part of the
issue is that point-blank-autassign is problematic and that helpers
should only be enabled for addresses that need it.

If you like I can resend the PR with an updated cover letter, or resend
with the dcc helper fix included as well.