netdev - Re: [PATCH rfc] netfilter: two xtables matches

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Date:	Wed, 5 Dec 2012 16:45:51 -0500
From:	Willem de Bruijn <willemb@...gle.com>
To:	Jan Engelhardt <jengelh@...i.de>
Cc:	netfilter-devel@...r.kernel.org, netdev@...r.kernel.org,
	Eric Dumazet <edumazet@...gle.com>,
	David Miller <davem@...emloft.net>,
	Patrick McHardy <kaber@...sh.net>, pablo@...filter.org
Subject: Re: [PATCH rfc] netfilter: two xtables matches

On Wed, Dec 5, 2012 at 3:00 PM, Jan Engelhardt <jengelh@...i.de> wrote:
> On Wednesday 2012-12-05 20:28, Willem de Bruijn wrote:
>
>>Somehow, the first part of this email went missing. Not critical,
>>but for completeness:
>>
>>These two patches each add an xtables match.
>>
>>The xt_priority match is a straighforward addition in the style of
>>xt_mark, adding the option to filter on one more sk_buff field. I
>>have an immediate application for this. The amount of code (in
>>kernel + userspace) to add a single check proved quite large.
>
> Hm so yeah, can't we just place this in xt_mark.c?

I'm happy to do so, but note that that breaks the custom of
having one static struct xt_$NAME for each file xt_$NAME.[ch].

It may be reasonable, as the same issue may keep popping up
as additional sk_buff fields are found useful for filtering. For
instance, skb->queue_mapping could be used in conjuction with
network flow classification (ethtool -N). All the ancillary data
accessible from BPF likely has some use and could be ported
to iptables (rxhash, pkt_type, ...).

To avoid rule explosion, I considered an xt_skbuff match rule that
applies the same mask operation, range and inversion tests, and
takes a field id to select the sk_buff field to operate on. I think
the BPF patch is a better long term solution.
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