netdev - Re: [PATCH 07/31] netfilter: ctnetlink: Support L3 protocol-filter on flush

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Date:   Fri, 3 May 2019 09:02:42 +0200
From:   Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:     Pablo Neira Ayuso <pablo@...filter.org>
Cc:     Florian Westphal <fw@...len.de>,
        Kristian Evensen <kristian.evensen@...il.com>,
        Netfilter Development Mailing list 
        <netfilter-devel@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH 07/31] netfilter: ctnetlink: Support L3 protocol-filter on
 flush

Le 02/05/2019 à 17:06, Pablo Neira Ayuso a écrit :
> On Thu, May 02, 2019 at 02:56:42PM +0200, Nicolas Dichtel wrote:
>> Le 02/05/2019 à 13:31, Pablo Neira Ayuso a écrit :
>>> On Thu, May 02, 2019 at 09:46:42AM +0200, Florian Westphal wrote:
>>>> Nicolas Dichtel <nicolas.dichtel@...nd.com> wrote:
>>>>> I understand your point, but this is a regression. Ignoring a field/attribute of
>>>>> a netlink message is part of the uAPI. This field exists for more than a decade
>>>>> (probably two), so you cannot just use it because nobody was using it. Just see
>>>>> all discussions about strict validation of netlink messages.
>>>>> Moreover, the conntrack tool exists also for ages and is an official tool.
>>>>
>>>> FWIW I agree with Nicolas, we should restore old behaviour and flush
>>>> everything when AF_INET is given.  We can add new netlink attr to
>>>> restrict this.
>>>
>>> Let's use nfgenmsg->version for this. This is so far set to zero. We
>>> can just update userspace to set it to 1, so family is used.
>>>
>>> The version field in the kernel size is ignored so far, so this should
>>> be enough. So we avoid that extract netlink attribute.
>>
>> Why making such a hack? If any userspace app set this field (simply because it's
>> not initialized), it will show up a new regression.
>> What is the problem of adding another attribute?
> 
> The version field was meant to deal with this case.
> 
> It has been not unused so far because we had no good reason.
> 
Fair point, agreed.


Thank you,
Nicolas