netdev - Re: TCP output handling bug ?

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Message-ID: <1408715790.5604.13.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Fri, 22 Aug 2014 06:56:30 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Dave Jones <davej@...hat.com>
Cc:	Stephen Hemminger <stephen@...workplumber.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>, netdev@...r.kernel.org
Subject: Re: TCP output handling bug ?

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.


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