netdev - Re: [PATCH net-next] net: fix possible wrong checksum generation

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Message-Id: <20130128.002801.200824996474874108.davem@davemloft.net>
Date:	Mon, 28 Jan 2013 00:28:01 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	pshelar@...ira.com, netdev@...r.kernel.org, jesse@...ira.com
Subject: Re: [PATCH net-next] net: fix possible wrong checksum generation

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Fri, 25 Jan 2013 22:34:37 -0800

> From: Eric Dumazet <edumazet@...gle.com>
> 
> Pravin Shelar mentioned that GSO could potentially generate
> wrong TX checksum if skb has fragments that are overwritten
> by the user between the checksum computation and transmit.
> 
> He suggested to linearize skbs but this extra copy can be
> avoided for normal tcp skbs cooked by tcp_sendmsg().
> 
> This patch introduces a new SKB_GSO_SHARED_FRAG flag, set
> in skb_shinfo(skb)->gso_type if at least one frag can be
> modified by the user.
> 
> Typical sources of such possible overwrites are {vm}splice(),
> sendfile(), and macvtap/tun/virtio_net drivers.
> 
> Tested:
 ...
> Performance of the SENDFILE is impacted by the extra allocation and
> copy, and because we use order-0 pages, while the TCP_STREAM uses
> bigger pages.
> 
> Reported-by: Pravin Shelar <pshelar@...ira.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Applied, thanks Eric.
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