netdev - Re: [PATCH nf-next 0/8] netfilter: untangle bridge and bridge netfilter

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Date:	Mon, 9 Mar 2015 14:02:53 +0100
From:	Pablo Neira Ayuso <pablo@...filter.org>
To:	Florian Westphal <fw@...len.de>
Cc:	netfilter-devel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH nf-next 0/8] netfilter: untangle bridge and bridge
 netfilter

Hi Florian,

On Thu, Mar 05, 2015 at 12:52:32AM +0100, Florian Westphal wrote:
> bridge_netfilter.h contains various helpers, some only used by br_netfilter,
> others however are also called in bridge or even ip stack.
> 
> Lets start untangling bridge, bridge netfilter, and the
> rest of the ip stack (esp. ip_fragment).
> 
> This changes ip_fragment() so that bridge netfilter
> can pass in the required information as arguments instead
> of using skb->nf_bridge to pass some extra information to it.
> 
> Another problem with br_netfilter and the way its plumbed to
> ip/ip6-tables (physdev match) is skb->nf_bridge.
> 
> nf_bridge is kmalloced blob with some extra information, including
> the bridge in and outports (mainly for iptables' physdev match).
> It also has various state bits so we know what manipulations
> have been performed by bridge netfilter on the skb (e.g.
> ppp header stripping).
>
> nf_bridge also provides scratch space where br_netfilter saves
> (and later restores) various things, e.g. ipv4 address for
> dnat detection, mac address to fix up ip fragmented skbs, etc.
> 
> But in almost all cases we can avoid using ->data completely.

I think one of the goals of this patchset is to prepare the removal of
that nf_bridge pointer from sk_buff which sounds as a good idea to me.

Did you consider to implement this scratchpad area using a per-cpu
area? I mean, something similar to what we used to have in
ip_conntrack for events:

http://www.cs.fsu.edu/~baker/devices/lxr/http/source/linux/net/netfilter/nf_conntrack_ecache.c?v=2.6.25#L65

Following that approach, I think we could avoid changing the
ip_fragment() interface. My concern is that these changes are too
specific of br_netfilter, which is not a good reference client of it
given all its design problems.

I'm preparing a new net-next batch, I can quickly take these three if
you agree:

1/8 bridge: move mac header copying into br_netfilter
2/8 netfilter: bridge: move nf_bridge_update_protocol to where its used
4/8 netfilter: bridge: refactor conditional in br_nf_dev_queue_xmit

Regarding 3/8, I think we can move that code to br_netfilter.c so we
reduce ifdef pollution a bit and keep as much of this monster code
fenced under that file. Please, see patch attached.

BTW, 6/8 I think needs some ifdef to make sure NF_CONNTRACK is in
placed. 7/8 needs NF_BRDIGE_MAX_MAC_HEADER_LENGTH which seems to have
a small typo in it, well these are dependent of 4/8 anyway.

Let me know, thanks a lot!

View attachment "0001-netfilter-brige-move-DNAT-helper-to-br_netfilter.patch" of type "text/x-diff" (4238 bytes)