netdev - Re: [PATCH v2] act_nat: fix the wrong checksum when addr isn't in old

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Message-ID: <20100530125811.GA8120@gondor.apana.org.au>
Date:	Sun, 30 May 2010 22:58:11 +1000
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	jamal <hadi@...erus.ca>
Cc:	Changli Gao <xiaosuo@...il.com>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH v2] act_nat: fix the wrong checksum when addr isn't in
	old_addr/mask

On Sun, May 30, 2010 at 08:43:41AM -0400, jamal wrote:
> 
> Copying Herbert, taking linux-kernel off...

Thanks Jamal.

> On Sun, 2010-05-30 at 08:26 +0800, Changli Gao wrote:
> > fix the wrong checksum when addr isn't in old_addr/mask
> > 
> > For TCP and UDP packets, when addr isn't in old_addr/mask we don't do SNAT or
> > DNAT, and we should not update layer 4 checksum.
> > 
> > Signed-off-by: Changli Gao <xiaosuo@...il.com>
> > ----
> >  net/sched/act_nat.c |    4 ++++
> >  1 file changed, 4 insertions(+)
> > diff --git a/net/sched/act_nat.c b/net/sched/act_nat.c
> > index d885ba3..5709494 100644
> > --- a/net/sched/act_nat.c
> > +++ b/net/sched/act_nat.c
> > @@ -159,6 +159,9 @@ static int tcf_nat(struct sk_buff *skb, struct tc_action *a,
> >  			iph->daddr = new_addr;
> >  
> >  		csum_replace4(&iph->check, addr, new_addr);
> > +	} else if ((iph->frag_off & htons(IP_OFFSET)) ||
> > +		   iph->protocol != IPPROTO_ICMP) {
> > +		goto out;
> >  	}

Yes the patch is correct.

However, the fact that you need this patch means that your act_nat
setup isn't perfect.  Ideally all the unNATed packets should be
filtered out before you hit act_nat.

Thanks,
-- 
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Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
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