netdev - Re: [PATCH 1/4] pch_gbe: fix the checksum fill to the error location

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Message-ID: <1341864963.2535.55.camel@bwh-desktop.uk.solarflarecom.com>
Date:	Mon, 9 Jul 2012 21:16:03 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Andy Cress <andy.cress@...kontron.com>
CC:	<netdev@...r.kernel.org>
Subject: Re: [PATCH 1/4] pch_gbe: fix the checksum fill to the error location

On Mon, 2012-07-09 at 06:30 -0700, Andy Cress wrote:
> From: Zhong Hongbo <hongbo.zhong@...driver.com>
> Date: Mon, 9 Apr 2012 10:51:28 +0800
> 
> Due to some unknown hardware limitations the pch_gbe hardware cannot
> calculate checksums when the length of network package is less
> than 64 bytes, where we will surprisingly encounter a problem of
> the destination IP incorrectly changed.
> 
> When forwarding network packages at the network layer the IP packages
> won't be relayed to the upper transport layer and analyzed there,
> consequently, skb->transport_header pointer will be mistakenly remained
> the same as that of skb->network_header, resulting in TCP checksum
> wrongly
> filled into the field of destination IP in IP header.
>
> We can fix this issue by manually calculate the offset of the TCP
> checksum
>  and update it accordingly.
[...]

You should be using skb_checksum_start_offset() instead.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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