netdev - Re: removing conntrack helper toggle to enable auto-assignment [was Re: b118509076b3 (probably) breaks my firewall]

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Date:   Mon, 19 Sep 2022 23:27:43 +0200
From:   Florian Westphal <fw@...len.de>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Florian Westphal <fw@...len.de>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Chris Clayton <chris2553@...glemail.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        regressions@...ts.linux.dev, netfilter-devel@...r.kernel.org,
        coreteam@...filter.org
Subject: Re: removing conntrack helper toggle to enable auto-assignment [was
 Re: b118509076b3 (probably) breaks my firewall]

Jakub Kicinski <kuba@...nel.org> wrote:
> I think we should do _something_ because we broke so many things 
> in this release if we let this rot until its smell reaches Linus -
> someone is getting yelled at...

Well, we can restore the knob and some strongly worded printk.
(or even tain/warn_on_once/whatever).

So its not like we no options, but autoassign=1 is a
problematic configuration and so it would prefer to finally get rid
of it.

> Now, Linus is usually okay with breaking uAPI if there is no other 
> way of preventing a security issue. But (a) we break autoload of
> all helpers and we only have security issue in one,

This isn't 100% correct either, because its not necessarliy about
a security bug.  Helpers (by design) make things reachable that
otherwise would not be, e.g. ftp with 'loose=1' modparam adds a
'from anywhere to x:y' reverse forward, so if client is behind nat
(and the helper is active) this can be used to expose a service to
a 3rd party (granted, this is unlikely, given its off by default).

> and (b) not loading
> the module doesn't necessarily mean removing the file (at least IMHO).

We did not disable module load, but loading a connection tracking
module has no effect anymore without the needed iptables (or nftables)
rules to tell the conntrack engine which connections need to be
monitored by which helper.