netdev - Re: b118509076b3 (probably) breaks my firewall

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Date:   Fri, 9 Sep 2022 19:21:47 +0100
From:   Chris Clayton <chris2553@...glemail.com>
To:     Pablo Neira Ayuso <pablo@...filter.org>,
        Florian Westphal <fw@...len.de>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        regressions@...muis.info
Subject: Re: b118509076b3 (probably) breaks my firewall



On 09/09/2022 11:19, Pablo Neira Ayuso wrote:
> On Thu, Sep 08, 2022 at 11:48:59PM +0200, Florian Westphal wrote:
>> Chris Clayton <chris2553@...glemail.com> wrote:
>>
>> [ CC Pablo ]
>>
>>> On 08/09/2022 20:19, Florian Westphal wrote:
>>>> Chris Clayton <chris2553@...glemail.com> wrote:
>>>>> Just a heads up and a question...
>>>>>
>>>>> I've pulled the latest and greatest from Linus' tree and built and installed the kernel. git describe gives
>>>>> v6.0-rc4-126-g26b1224903b3.
>>>>>
>>>>> I find that my firewall is broken because /proc/sys/net/netfilter/nf_conntrack_helper no longer exists. It existed on an
>>>>> -rc4 kernel. Are changes like this supposed to be introduced at this stage of the -rc cycle?
>>>>
>>>> The problem is that the default-autoassign (nf_conntrack_helper=1) has
>>>> side effects that most people are not aware of.
>>>>
>>>> The bug that propmpted this toggle from getting axed was that the irc (dcc) helper allowed
>>>> a remote client to create a port forwarding to the local client.
>>>
>>>
>>> Ok, but I still think it's not the sort of change that should be introduced at this stage of the -rc cycle.
>>> The other problem is that the documentation (Documentation/networking/nf_conntrack-sysctl.rst) hasn't been updated. So I
>>> know my firewall is broken but there's nothing I can find that tells me how to fix it.
>>
>> Pablo, I don't think revert+move the 'next' will avoid this kinds of
>> problems, but at least the nf_conntrack-sysctl.rst should be amended to
>> reflect that this was removed.
> 
> I'll post a patch to amend the documentation.
> 
>> I'd keep it though because people that see an error wrt. this might be
>> looking at nf_conntrack-sysctl.rst.
>>
>> Maybe just a link to
>> https://home.regit.org/netfilter-en/secure-use-of-helpers/?
>>
but
I'm afraid that document isn't much use to a "Joe User" like me. It's written by people who know a lot about the subject
matter to be read by other people who know a lot about the subject matter.

>> What do you think?
> 
> I'll update netfilter.org to host a copy of the github sources.
> 
> We have been announcing this going deprecated for 10 years...


That may be the case, it should be broken before -rc1 is released. Breaking it at -rc4+ is, I think, a regression!
Adding Thorsten Leemuis to cc list