netdev - Re: [PATCH v3] tcp: fix wrong checksum calculation on MTU probing

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Date:   Fri, 23 Sep 2016 07:58:39 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     douglascs@...hos.com.br
Cc:     sergei.shtylyov@...entembedded.com, kuznet@....inr.ac.ru,
        jmorris@...ei.org, yoshfuji@...ux-ipv6.org, kaber@...sh.net,
        netdev@...r.kernel.org
Subject: Re: [PATCH v3] tcp: fix wrong checksum calculation on MTU probing

From: Douglas Caetano dos Santos <douglascs@...hos.com.br>
Date: Thu, 22 Sep 2016 15:52:04 -0300

> With TCP MTU probing enabled and offload TX checksumming disabled,
> tcp_mtu_probe() calculated the wrong checksum when a fragment being copied
> into the probe's SKB had an odd length. This was caused by the direct use
> of skb_copy_and_csum_bits() to calculate the checksum, as it pads the
> fragment being copied, if needed. When this fragment was not the last, a
> subsequent call used the previous checksum without considering this
> padding.
> 
> The effect was a stale connection in one way, as even retransmissions
> wouldn't solve the problem, because the checksum was never recalculated for
> the full SKB length.
> 
> Signed-off-by: Douglas Caetano dos Santos <douglascs@...hos.com.br>

Applied and queued up for -stable, thanks.