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Date:	Fri, 22 Aug 2014 10:41:18 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	davej@...hat.com, stephen@...workplumber.org,
	alan@...rguk.ukuu.org.uk, netdev@...r.kernel.org, ycheng@...gle.com
Subject: Re: TCP output handling bug ?

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Fri, 22 Aug 2014 06:56:30 -0700

CC:'ing Yuchung Cheng

> On Thu, 2014-08-21 at 22:13 -0400, Dave Jones wrote:
>> On Thu, Aug 21, 2014 at 05:24:45PM -0700, Stephen Hemminger wrote:
>>  > On Thu, 21 Aug 2014 19:02:08 +0100
>>  > Alan Cox <alan@...rguk.ukuu.org.uk> wrote:
>>  > 
>>  > > 
>>  > > tcp_send_syn_data:
>>  > > 
>>  > >         TCP_SKB_CB(data)->tcp_flags &= ~TCPHDR_SYN;
>>  > >         TCP_SKB_CB(data)->tcp_flags = (TCPHDR_ACK|TCPHDR_PSH);
>>  > > 
>>  > > the reporter has a point 8)
>>  > > 
>>  > > https://bugzilla.kernel.org/show_bug.cgi?id=82101
>>  > 
>>  > I wonder if covertity or smatch could be smart enough to catch this kind of bug?
>> 
>> For coverity: it should be, but isn't :)
>> I've pointed them at the bugzilla, maybe they can add a check in a
>> future update.
>> 
>> I bet this isn't the only instance of a bug like this left in the tree.
>> We've definitely had similar cases before.
>> 
>> 	Dave
> 
> There is no bug here as a matter of fact.
> 
> You can simply remove the first line, as it is useless.
> 
> -	TCP_SKB_CB(data)->tcp_flags &= ~TCPHDR_SYN;
> 
> At the end of the day, data segment has ACK and PSH flags only.

What about ECE/CWR?
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