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

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Message-ID: <20100730143016.GA10543@gondor.apana.org.au>
Date:	Fri, 30 Jul 2010 22:30:16 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Changli Gao <xiaosuo@...il.com>
Cc:	Jamal Hadi Salim <hadi@...erus.ca>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, Patrick McHardy <kaber@...sh.net>
Subject: Re: [PATCH] act_nat: the checksum of ICMP doesn't have pseudo
	header

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>

Thanks,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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