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

[David Miller <davem@davemloft.net>]

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

> From: Eric Dumazet <edumazet@google.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@nicira.com>
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Applied, thanks Eric.