netdev - Re: Regression with commit 971f10eca186 ("tcp: better TCP_SKB

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Date:	Mon, 22 Dec 2014 08:15:39 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	nicolas.dichtel@...nd.com
Cc:	netdev <netdev@...r.kernel.org>, Eric Dumazet <edumazet@...gle.com>
Subject: Re: Regression with commit 971f10eca186 ("tcp: better TCP_SKB_CB
 layout to reduce cache line misses")

On Mon, 2014-12-22 at 16:17 +0100, Nicolas Dichtel wrote:
> One of our engineer (Huaibin Wang <huaibin.wang@...nd.com>) has reported and
> analysed this bug:
> 
> This commit introduces a regression with IPv6 + IPsec transport + TCP.
> 
> In TCP (net/ipv6/tcp_ipv6.c), xfrm6_policy_check() is called and thus, after
> some intermediate functions, _decode_session6() is also called.
> 
> This function uses IP6CB() (u8 nexthdr = nh[IP6CB(skb)->nhoff]), which is wrong
> becauses it has been moved to the end of TCP_SKB_CB().
> 
> Not sure what is the best way to fix this, any suggestion?

Thanks for the report

Presumably tcp_v6_rcv() needs to be reordered so that
xfrm6_policy_check() calls are done before the CB swap.

swap should probably be done right before bh_lock_sock_nested()

I am currently traveling and I am not sure if I can get Internet access
to post a patch soon.



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