netdev - Re: [PATCH net] sit: Set skb->protocol properly in ipip6_tunnel

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Date:   Mon, 28 Nov 2016 15:00:30 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     eric.dumazet@...il.com
Cc:     alexander.duyck@...il.com, sfr@...b.auug.org.au, elicooper@....com,
        netdev@...r.kernel.org
Subject: Re: [PATCH net] sit: Set skb->protocol properly in
 ipip6_tunnel_xmit()

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Mon, 28 Nov 2016 10:32:15 -0800

> On Mon, 2016-11-28 at 10:17 -0800, Eric Dumazet wrote:
> 
>> I was referring to Stephen bug report.
>> 
>> It appears that Eli changelog was not very precise, because his bug was
>> because of XFRM being involved.
>> 
>> xfrm_output() -> xfrm_output_gso() -> skb_gso_segment()
>> 
>> So XFRM calls skb_gso_segment() before ip_output() or
>> ip6_finish_output2() had a chance to change skb->protocol
> 
> So maybe the real fix would be to set skb->protocol at the right place,
> before xfrm can be called, instead of chasing all skb producers ;)

And the key for this would be dst_output() invocations.