netdev - Re: [PATCH nf-next 3/3] netfilter: Introduce egress hook

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Date:   Tue, 28 Apr 2020 22:11:19 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Lukas Wunner <lukas@...ner.de>, Laura Garcia <nevola@...il.com>
Cc:     Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        Florian Westphal <fw@...len.de>,
        Netfilter Development Mailing list 
        <netfilter-devel@...r.kernel.org>, coreteam@...filter.org,
        netdev@...r.kernel.org, Martin Mares <mj@....cz>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Thomas Graf <tgraf@...g.ch>,
        Alexei Starovoitov <ast@...nel.org>,
        David Miller <davem@...emloft.net>
Subject: Re: [PATCH nf-next 3/3] netfilter: Introduce egress hook

Hey Lukas,

On 4/23/20 6:05 PM, Lukas Wunner wrote:
> On Thu, Apr 23, 2020 at 04:44:44PM +0200, Laura Garcia wrote:
>> On Sun, Mar 15, 2020 at 2:29 PM Pablo Neira Ayuso <pablo@...filter.org> wrote:
>>> On Sat, Mar 14, 2020 at 01:12:02AM +0100, Daniel Borkmann wrote:
>>>> On 3/13/20 3:55 PM, Pablo Neira Ayuso wrote:
>>>>> We have plans to support for NAT64 and NAT46, this is the right spot
>>>>> to do this mangling. There is already support for the tunneling
>>>>
>>>> But why is existing local-out or post-routing hook _not_ sufficient for
>>>> NAT64 given it being IP based?
>>>
>>> Those hooks are not coming at the end of the IP processing. There is
>>> very relevant IP code after those hooks that cannot be bypassed such
>>> as fragmentation, tunneling and neighbour output. Such transformation
>>> needs to happen after the IP processing, exactly from where Lukas is
>>> proposing.
>>>
>>> [...]
>>>>> infrastructure in netfilter from ingress, this spot from egress will
>>>>> allow us to perform the tunneling from here. There is also no way to
>>>>> drop traffic generated by dhclient, this also allow for filtering such
>>>>> locally generated traffic. And many more.
>>
>> Any chance to continue with this approach? I'm afraid outbound
>> af_packets also could not be filtered without this hook.
> 
> Thanks Laura, good to hear there's interest in the functionality.
> 
> Daniel submitted a revert of this series but didn't cc me:
> 
> https://lore.kernel.org/netdev/bbdee6355234e730ef686f9321bd072bcf4bb232.1584523237.git.daniel@iogearbox.net/
> 
> In the ensuing discussion it turned out that the performance argument
> may be addressed by a rearrangement of sch_handle_egress() and
> nf_egress() invocations.  I could look into amending the series
> accordingly and resubmitting, though I'm currently swamped with
> other work.

The rework of these hooks is still on my todo list, too swamped with
other stuff as well right now, but I'll see to have a prototype this
net-next development cycle.

Thanks,
Daniel