netdev - Re: [PATCH net-next] sunvnet: don't change gso data on clones

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Message-ID: <54DC1B3F.8000507@oracle.com>
Date:	Wed, 11 Feb 2015 22:17:19 -0500
From:	David L Stevens <david.stevens@...cle.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH net-next] sunvnet: don't change gso data on clones

Yes, I've seen that patch. The bug I'm fixing has the same symptoms,
but the mangling is being done by the sunvnet driver and the fix is
the same-- don't mangle packets that are cloned (and unclone them if you
need to mangle them).

The original sunvnet code changed gso_size temporarily, but that still
had a race where TCP could see the driver-modified gso_size with low probability
and end up with a negative packets-in-flight.

The unclone removes that bug, created (by me) after your fix, but in the sunvnet driver
with the addition of TSO support.

						+-DLS

On 02/11/2015 09:52 PM, Eric Dumazet wrote:

> 
> Well, we had a very hard to find bug in TCP stack, I want to make sure
> we fixed all relevant points.
> 
> commit c52e2421f7368fd36cbe330d2cf41b10452e39a9
> Author: Eric Dumazet <edumazet@...gle.com>
> Date:   Tue Oct 15 11:54:30 2013 -0700
> 
>     tcp: must unclone packets before mangling them
>     
>     TCP stack should make sure it owns skbs before mangling them.
...
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