netdev - Re: [PATCH nf-next v3 0/3] Netfilter egress hook

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Date:   Fri, 28 Aug 2020 11:14:25 +0200
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>,
        Lukas Wunner <lukas@...ner.de>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        Florian Westphal <fw@...len.de>
Cc:     netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        netdev@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Thomas Graf <tgraf@...g.ch>, Laura Garcia <nevola@...il.com>,
        David Miller <davem@...emloft.net>
Subject: Re: [PATCH nf-next v3 0/3] Netfilter egress hook



On 8/28/20 12:14 AM, Daniel Borkmann wrote:
> Hi Lukas,
> 
> On 8/27/20 10:55 AM, Lukas Wunner wrote:
>> Introduce a netfilter egress hook to allow filtering outbound AF_PACKETs
>> such as DHCP and to prepare for in-kernel NAT64/NAT46.
> 
> Thinking more about this, how will this allow to sufficiently filter AF_PACKET?
> It won't. Any AF_PACKET application can freely set PACKET_QDISC_BYPASS without
> additional privileges and then dev_queue_xmit() is being bypassed in the host ns.
> This is therefore ineffective and not sufficient. (From container side these can
> be caught w/ host veth on ingress, but not in host ns, of course, so hook won't
> be invoked.)


Presumably dev_direct_xmit() could be augmented to support the hook.

dev_direct_xmit() (packet_direct_xmit()) was introduced to bypass qdisc,
not to bypass everything.