netdev - Re: [PATCH 1/4] netfilter: xt_connlimit: fix daddr connlimit in SNAT scenario

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Message-ID: <AANLkTinZiVbVttzNuGdShC25=BtwJUzhSX_YZBxAr+qF@mail.gmail.com>
Date:	Tue, 15 Mar 2011 09:30:04 +0800
From:	Changli Gao <xiaosuo@...il.com>
To:	Jan Engelhardt <jengelh@...ozas.de>
Cc:	Patrick McHardy <kaber@...sh.net>,
	"David S. Miller" <davem@...emloft.net>,
	netfilter-devel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH 1/4] netfilter: xt_connlimit: fix daddr connlimit in SNAT scenario

On Tue, Mar 15, 2011 at 9:16 AM, Jan Engelhardt <jengelh@...ozas.de> wrote:
>
>
> The original tuple may not be updated, but the reply tuple is.
> And we are taking the reply tuple in
>
>        tuple_ptr = &ct->tuplehash[IP_CT_DIR_REPLY].tuple;
>
> which is subsequently copied to conn->tuple on the first invocation.
>
> Afterwards, SNAT will update ct->tuplehash[reply].tuple, and so
> conn->tuple is outdated. Calling nf_conntrack_find_get(conn->tuple)
> in count_them would then fail, would it not?
>

After my patch, tuple is only used to look up the corresponding
conntrack. And as you know, one conntrack has two tuples, you can look
up a conntrack by either one. The old implementation uses the
conn->tuple.src.u3 to save target address, so you need to use the
reply tuple to work around the DNAT issue. In my patch, the target
address isn't saved in conn->tuple.src.u3 but in conn->addr, so we can
use the constant tuple in the original direction to look up the
corresponding conntrack in count_them(). No reply tuple involved, no
failed nf_conntrack_find_get().

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