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

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Date:	Fri, 30 Jul 2010 18:10:19 +0800
From:	Changli Gao <xiaosuo@...il.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Jamal Hadi Salim <hadi@...erus.ca>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] act_nat: the checksum of ICMP doesn't have pseudo header

On Fri, Jul 30, 2010 at 5:09 PM, Herbert Xu <herbert@...dor.apana.org.au> wrote:
> On Fri, Jul 30, 2010 at 08:04:18AM +0800, Changli Gao wrote:
>> after updating the value of the ICMP payload, inet_proto_csum_replace4() should
>> be called with zero pseudohdr.
>>
>> Signed-off-by: Changli Gao <xiaosuo@...il.com>
>
> No, the code is correct as is.  We need to update the checksum
> even if the checksum is partial, which is what the 1 is for.
>

Is it really necessary, and I have noticed that netfilter doesn't call
inet_proto_csum_replace4 in this way.

static bool
icmp_manip_pkt(struct sk_buff *skb,
               unsigned int iphdroff,
               const struct nf_conntrack_tuple *tuple,
               enum nf_nat_manip_type maniptype)
{
        const struct iphdr *iph = (struct iphdr *)(skb->data + iphdroff);
        struct icmphdr *hdr;
        unsigned int hdroff = iphdroff + iph->ihl*4;

        if (!skb_make_writable(skb, hdroff + sizeof(*hdr)))
                return false;

        hdr = (struct icmphdr *)(skb->data + hdroff);
        inet_proto_csum_replace2(&hdr->checksum, skb,
                                 hdr->un.echo.id, tuple->src.u.icmp.id, 0);
        hdr->un.echo.id = tuple->src.u.icmp.id;
        return true;
}

Thanks.

-- 
Regards,
Changli Gao(xiaosuo@...il.com)
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