netdev - Re: [PATCH net] tcp: do not mangle skb->cb[] in tcp_make

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Date:   Fri, 03 Nov 2017 14:32:14 +0900 (KST)
From:   David Miller <davem@...emloft.net>
To:     eric.dumazet@...il.com
Cc:     cpaasch@...le.com, edumazet@...gle.com, netdev@...r.kernel.org
Subject: Re: [PATCH net] tcp: do not mangle skb->cb[] in tcp_make_synack()

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Thu, 02 Nov 2017 12:30:25 -0700

> From: Eric Dumazet <edumazet@...gle.com>
> 
> Christoph Paasch sent a patch to address the following issue :
> 
> tcp_make_synack() is leaving some TCP private info in skb->cb[],
> then send the packet by other means than tcp_transmit_skb()
> 
> tcp_transmit_skb() makes sure to clear skb->cb[] to not confuse
> IPv4/IPV6 stacks, but we have no such cleanup for SYNACK.
> 
> tcp_make_synack() should not use tcp_init_nondata_skb() :
> 
> tcp_init_nondata_skb() really should be limited to skbs put in write/rtx
> queues (the ones that are only sent via tcp_transmit_skb())
> 
> This patch fixes the issue and should even save few cpu cycles ;)
> 
> Fixes: 971f10eca186 ("tcp: better TCP_SKB_CB layout to reduce cache line misses")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: Christoph Paasch <cpaasch@...le.com>

Applied and queued up for -stable.