linux-kernel - Re: [patch v2.3 3/4] IPVS: make FTP work with full NAT support

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Date:	Sat, 10 Jul 2010 10:54:21 +0900
From:	Simon Horman <horms@...ge.net.au>
To:	Patrick McHardy <kaber@...sh.net>
Cc:	lvs-devel@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, netfilter@...r.kernel.org,
	netfilter-devel@...r.kernel.org,
	Malcolm Turnbull <malcolm@...dbalancer.org>,
	Wensong Zhang <wensong@...ux-vs.org>,
	Julius Volz <julius.volz@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Hannes Eder <heder@...gle.com>
Subject: Re: [patch v2.3 3/4] IPVS: make FTP work with full NAT support

On Fri, Jul 09, 2010 at 05:24:56PM +0200, Patrick McHardy wrote:
> Am 07.07.2010 08:53, schrieb Simon Horman:
> > On Tue, Jul 06, 2010 at 01:43:44PM +0200, Patrick McHardy wrote:
> >> Simon Horman wrote:
> >>> @@ -219,19 +358,23 @@ static int ip_vs_ftp_out(struct ip_vs_ap
> >>> 		buf_len = strlen(buf);
> >>> +		ct = nf_ct_get(skb, &ctinfo);
> >>> +		ret = nf_nat_mangle_tcp_packet(skb,
> >>> +					       ct,
> >>> +					       ctinfo,
> >>> +					       start-data,
> >>> +					       end-start,
> >>> +					       buf,
> >>> +					       buf_len);
> >>> +
> >>> +		if (ct && ct != &nf_conntrack_untracked)
> >> This does not make sense, you're already using the conntrack above
> >> in the call to nf_nat_mangle_tcp_packet(), so the check should
> >> probably happen before that. You also should be checking the
> >> return value of nf_nat_mangle_tcp_packet() before setting up the
> >> expectation.
> >>
> >>> +			ip_vs_expect_related(skb, ct, n_cp,
> >>> +					     IPPROTO_TCP, NULL, 0);
> > 
> > Good point. Is this better?
> > 
> > 		ct = nf_ct_get(skb, &ctinfo);
> > 		if (ct && !nf_ct_is_untracked()) {
> > 			ret = nf_nat_mangle_tcp_packet(skb, ct, ctinfo,
> > 						       start-data, end-start,
> > 						       buf, buf_len);
> > 			if (ret)
> > 				ip_vs_expect_related(skb, ct, n_cp,
> > 						     IPPROTO_TCP, NULL, 0);
> 
> Yes, that's better, although we're usually dropping packets
> when mangling fails. This can only happen under memory pressure,
> the assumption is that we might be able to properly mangle
> the packet when it is retransmitted.

I didn't notice this either, but ret will be end up being the return value
of ip_vs_ftp_out(), and if that is zero the packet will be dropped.

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