netdev - Re: b118509076b3 (probably) breaks my firewall

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Date:   Fri, 9 Sep 2022 19:31:31 +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@...ts.linux.dev
Subject: Re: b118509076b3 (probably) breaks my firewall

[the address I used for regressions was bounced. Using the right one...]

On 09/09/2022 19:21, Chris Clayton wrote:
> 
> 
> 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