From mboxrd@z Thu Jan  1 00:00:00 1970
From: Pablo Neira Ayuso <pablo@netfilter.org>
Subject: Re: [PATCH] xt_owner: enable xt_owner on INPUT chain
Date: Wed, 4 Sep 2013 14:34:59 +0200
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Cc: netfilter-devel@vger.kernel.org, Patrick McHardy <kaber@trash.net>,
	Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>,
	"David S. Miller" <davem@davemloft.net>
To: valentina.giusti@bmw-carit.de
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On Fri, Aug 30, 2013 at 02:43:43PM +0200, valentina.giusti@bmw-carit.de wrote:
> From: Valentina Giusti <valentina.giusti@bmw-carit.de>
> 
> Since (41063e9 ipv4: Early TCP socket demux), we can apply the owner
> extension on the INPUT chain and match established TCP sockets.
> However, because of the same commit, we can have skb->sk pointing to a
> timewait socket, in which case accessing skb->sk->sk_socket is invalid.

This only works for established TCP sockets. Thus, this rule:

-A INPUT -m owner --socket-exists -j ACCEPT
-A OUTPUT -m owner --socket-exists -j ACCEPT

are semantically different depending on the path.