netdev - Re: [patch net-next 2/3] netfilter: ip6_tables: use reasm skb for matching

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Date:	Wed, 6 Nov 2013 16:29:07 +0100
From:	Jiri Pirko <jiri@...nulli.us>
To:	Patrick McHardy <kaber@...sh.net>
Cc:	Florian Westphal <fw@...len.de>, netdev@...r.kernel.org,
	davem@...emloft.net, pablo@...filter.org,
	netfilter-devel@...r.kernel.org, yoshfuji@...ux-ipv6.org,
	kadlec@...ckhole.kfki.hu, mleitner@...hat.com,
	kuznet@....inr.ac.ru, jmorris@...ei.org, wensong@...ux-vs.org,
	horms@...ge.net.au, ja@....bg, edumazet@...gle.com,
	pshelar@...ira.com, jasowang@...hat.com,
	alexander.h.duyck@...el.com, coreteam@...filter.org
Subject: Re: [patch net-next 2/3] netfilter: ip6_tables: use reasm skb for
 matching

Wed, Nov 06, 2013 at 03:51:04PM CET, kaber@...sh.net wrote:
>On Wed, Nov 06, 2013 at 03:44:53PM +0100, Jiri Pirko wrote:
>> Wed, Nov 06, 2013 at 03:33:49PM CET, fw@...len.de wrote:
>> >Jiri Pirko <jiri@...nulli.us> wrote:
>> >> >> >So if someone wants to change this, simply *only* pass the reassembled
>> >> >> >packet through the netfilter hooks and drop the fragments, as in IPv4.
>> >> >> 
>> >> >> This is unfortunatelly not possible because in forwarding use case, the
>> >> >> fragments have to be send out as they come in.
>> >> >
>> >> >No, the IPv6 NAT patches fixed that, we still do proper refragmentation
>> >> >and we still respect the original fragment sizes, thus are not responsible
>> >> >for potentially exceeding the PMTU on the following path.
>> >> 
>> >> Can you please point where this is done. Where the original fragment
>> >> sizes are stored and in which code are they restored? Thanks.
>> >
>> >Patrick is probably talking about
>> >
>> >commit 4cdd34084d539c758d00c5dc7bf95db2e4f2bc70
>> >(netfilter: nf_conntrack_ipv6: improve fragmentation handling)
>> >which introduces 'frag_max_size' in inet6_skb_parm struct.
>
>Indeed.
>
>> Thanks for the pointer. Interestingly though, according to my testing,
>> if reassembled packet would fit into outdev mtu, it is not fragmented
>> to the original frag size and it is send as single big packet. That is
>> I believe not correct.
>
>Hmm right, that wasn't the intention. We currently only use frag_max_size
>to send PKT_TOOBIG messages if the size exceeds the MTU, but not to trigger
>fragmentation itself.
>
>We probably need to handle this in ip6_finish_output(). Would you mind
>fixing this up as well in your patches?

I'm working on it atm.


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