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

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Date:	Wed, 29 Aug 2012 14:28:53 +0200 (MEST)
From:	Patrick McHardy <kaber@...sh.net>
To:	Jesper Dangaard Brouer <brouer@...hat.com>
cc:	Hans Schillstrom <hans@...illstrom.com>, netdev@...r.kernel.org,
	lvs-devel@...r.kernel.org, Julian Anastasov <ja@....bg>,
	Simon Horman <horms@...ge.net.au>,
	Wensong Zhang <wensong@...ux-vs.org>,
	netfilter-devel@...r.kernel.org
Subject: Re: Re[3]: [PATCH 2/3] ipvs: Fix faulty IPv6 extension header 
 handling in IPVS

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

> To Hans and Patrick,
>
> On Mon, 2012-08-27 at 14:02 +0200, Patrick McHardy wrote:
>> On Mon, 27 Aug 2012, Hans Schillstrom wrote:
>>
>>>>>>
>>>>>> On Mon, 20 Aug 2012, Jesper Dangaard Brouer wrote:
>>>>>>
>>>>>>> Based on patch from: Hans Schillstrom
>>>>>>>
>>>>>>> IPv6 headers must be processed in order of appearance,
>>>>>>> neither can it be assumed that Upper layer headers is first.
>>>>>>> If anything else than L4 is the first header IPVS will throw it.
>>>>>>>
>>>>>>> IPVS will write SNAT & DNAT modifications at a fixed pos which
>>>>>>> will corrupt the message. Proper header position must be found
>>>>>>> before writing modifying packet.
>>>>>>>
>>>>>>> This patch contains a lot of API changes.  This is done, to avoid
>>>>>>> the costly scan of finding the IPv6 headers, via ipv6_find_hdr().
>>>>>>> Finding the IPv6 headers is done as early as possible, and passed
>>>>>>> on as a pointer "struct ip_vs_iphdr *" to the affected functions.
>>>>>>
>>>>>> 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?

I don't think we can do much better than using inet6_skb_parm. I think
the main question is whether it is really worth it, the iteration 
shouldn't be that expensive in most cases.
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