netdev - Re: [PATCH] act_nat: the checksum of ICMP doesn't have pseudo header

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Message-Id: <20100731.220518.212680999.davem@davemloft.net>
Date:	Sat, 31 Jul 2010 22:05:18 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	herbert@...dor.apana.org.au
Cc:	xiaosuo@...il.com, hadi@...erus.ca, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, kaber@...sh.net
Subject: Re: [PATCH] act_nat: the checksum of ICMP doesn't have pseudo
 header

From: Herbert Xu <herbert@...dor.apana.org.au>
Date: Fri, 30 Jul 2010 22:30:16 +0800

> On Fri, Jul 30, 2010 at 10:16:05PM +0800, Changli Gao wrote:
>> 
>> I know we need to update the ICMP checksum if we alter the payload(the
>> inner IP header here) of ICMP. But I doubt if the update is really
>> necessary if the checksum is partial, as the   checksum will be done
>> later(by ether skb_checksum_help() or NIC hardware). In fact, as there
>> isn't any pseudo header, the icmph->checksum should be always ZERO,
>> otherwise skb_checksum_help() or NIC will give the wrong checksums,
>> when the checksum is partial.
> 
> Actually you are right.  I suppose the only reason this has never
> shown up is because CHEKSUM_PARTIAL doesn't usually occur with
> forwarded packets.
> 
> Acked-by: Herbert Xu <herbert@...dor.apana.org.au>

Also applied, thanks.

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