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:

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On Mon, 2012-08-27 at 14:02 +0200, Patrick McHardy wrote:

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On Mon, 27 Aug 2012, Hans Schillstrom wrote:

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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.