netdev - Re: [PATCH nf-next,RFC 5/5] netfilter: Introduce egress hook

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Date:   Thu, 31 Oct 2019 23:39:58 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Lukas Wunner <lukas@...ner.de>
Cc:     Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        Florian Westphal <fw@...len.de>,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        netdev@...r.kernel.org, Martin Mares <mj@....cz>
Subject: Re: [PATCH nf-next,RFC 5/5] netfilter: Introduce egress hook

On 10/31/19 2:41 PM, Lukas Wunner wrote:
> Commit e687ad60af09 ("netfilter: add netfilter ingress hook after
> handle_ing() under unique static key") introduced the ability to
> classify packets on ingress.
> 
> Allow the same on egress.
> 
> The need for this arose because I had to filter egress packets which do
> not match a specific ethertype.  The most common solution appears to be

This seems like a /very/ weak justification for something that sits in
critical fastpath. NAK.

> to enslave the interface to a bridge and use ebtables, but that's
> cumbersome to configure and comes with a (small) performance penalty.
> An alternative approach is tc, but that doesn't afford equivalent
> matching options as netfilter.
Hmm, have you tried tc BPF on the egress hook (via sch_cls_act -> cls_bpf)?

> people have expressed a desire for egress filtering in the past:
> 
> https://www.spinics.net/lists/netfilter/msg50038.html

Adding another hook to catch misconfigurations of NAT in postrouting ...?

> https://unix.stackexchange.com/questions/512371

This talks about filtering / limiting ARP packets which can be done today
easily with existing means, including writing ARP responders sitting on tc
ingress/egress hook.

> An egress hook therefore seems like an obvious addition.
> 
> Signed-off-by: Lukas Wunner <lukas@...ner.de>
> Cc: Daniel Borkmann <daniel@...earbox.net>