Re[2]: Re[3]: [PATCH 2/3] ipvs: Fix faulty IPv6 extension header handl

To: "Patrick McHardy" <kaber@xxxxxxxxx>
Subject: Re[2]: Re[3]: [PATCH 2/3] ipvs: Fix faulty IPv6 extension header handling in IPVS
Cc: "Jesper Dangaard Brouer" <brouer@xxxxxxxxxx>, netdev@xxxxxxxxxxxxxxx, lvs-devel@xxxxxxxxxxxxxxx, "Julian Anastasov" <ja@xxxxxx>, "Simon Horman" <horms@xxxxxxxxxxxx>, "Wensong Zhang" <wensong@xxxxxxxxxxxx>, netfilter-devel@xxxxxxxxxxxxxxx
From: "Hans Schillstrom" <hans@xxxxxxxxxxxxxxx>
Date: Wed, 29 Aug 2012 14:36:01 +0200 (CEST)
>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.

Well, if we start using it it could be worth it...

As a first sketch I think adding protocol and offset to inet6_skb_parm would be 
and  then scan the header in ipv6_defrag() which is a quite early ...


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