netdev - Re: [PATCH 2/3] ipvs: Fix faulty IPv6 extension header handling in IPVS

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Date:	Wed, 29 Aug 2012 14:34:34 +0200 (MEST)
From:	Patrick McHardy <kaber@...sh.net>
To:	Jesper Dangaard Brouer <brouer@...hat.com>
cc:	Hans Schillstrom <hans@...illstrom.com>,
	Hans Schillstrom <hans.schillstrom@...csson.com>,
	netdev@...r.kernel.org, lvs-devel@...r.kernel.org,
	Julian Anastasov <ja@....bg>,
	Simon Horman <horms@...ge.net.au>,
	netfilter-devel@...r.kernel.org
Subject: Re: [PATCH 2/3] ipvs: Fix faulty IPv6 extension  header handling in
 IPVS

On Wed, 29 Aug 2012, Jesper Dangaard Brouer wrote:

> To Patrick,
>
> On Wed, 2012-08-29 at 11:47 +0200, Hans Schillstrom wrote:
>>>
>>> On Mon, 2012-08-27 at 14:02 +0200, Patrick McHardy wrote:
>>>> On Mon, 27 Aug 2012, Hans Schillstrom wrote:
>>>>
>>>>>>>> How about we change netfilter to set up the skb's transport header
>>>>>>>> at an early time so we can avoid all (most of) these header scans
>>>>>>>> in netfilter?
>>>>>>>
>>>>>>> I think that would be great, maybe it should be global i.e. not only a netfilter issue.
>>>>>>
>>>>>> I think in most other cases the headers are supposed to be processed
>>>>>> sequentially. One problem though - to be useful for netfilter/IPVS
>>>>>> we'd also need to store the transport layer protocol somewhere.
>>>>>
>>>>> I guess that's the problem, adding it to the skb will not be popular ....
>>>>> Right now I don't have a good solution, maybe a more generic netfilter ptr in the skb ...
>>>>
>>>> I guess inet6_skb_parm will be at least slightly more popular than
>>>> adding it to the skb itself. The netfilter pointers are all used for
>>>> optional things, so we can't really add it to any of those.
>>>
>>> Okay, but how do we go from here?
>>>
>>> Hans, should this hold back the patch ("ipvs: Fix faulty IPv6 extension
>>> header handling in IPVS").  Or should we pursue our patch, and circle
>>> back later once e.g. Patrick have found a generic solution for IPv6
>>> transport header handling?
>>
>> Should we give it a try to put it in inet6_skb_parm
>> and minimize what we put there ?
>> I think it could be worth it.
>
> Okay, but then I do need some help and guidance, especially from
> Patrick, think.
>
> First of all, where in the netfilter code, should we update the new
> fields in inet6_skb_parm?

Good question. I think we'd need at least three spots since every one
of these subsystems can be used indepedently from each other:

- conntrack/IPVS: PRE_ROUTING/LOCAL_OUT at lowest priority
- ip6tables: first time packet hits ip6t_do_table()?

Actually, looking at ipv6_rcv(), this might not work at all since it
sets skb->transport_header to the first header following the IPv6
header. This is used when processing extension headers by IPv6.


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