netdev - Re: sk->sk_socket seems to disappear before connection termination

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Message-ID: <4CDBCCD0.9040807@trash.net>
Date:	Thu, 11 Nov 2010 12:00:32 +0100
From:	Patrick McHardy <kaber@...sh.net>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	Jan Engelhardt <jengelh@...ozas.de>,
	David Howells <dhowells@...hat.com>,
	Netfilter Developer Mailing List 
	<netfilter-devel@...r.kernel.org>, netdev@...r.kernel.org,
	Rafał Maj <rafal.maj.it@...il.com>
Subject: Re: sk->sk_socket seems to disappear before connection termination

On 10.11.2010 18:37, Eric Dumazet wrote:
> Le mercredi 10 novembre 2010 à 18:17 +0100, Jan Engelhardt a écrit :
>> On Wednesday 2010-11-10 17:44, Eric Dumazet wrote:
>>>
>>> [ 9920.234680] ipt_LOG: sk=ffff880118bd32c0 sk->sk_socket=ffff88011d0d8c00 file=ffff88011cd4e100
>>> [ 9920.234731] IN= OUT=eth1 SRC=192.168.20.108 DST=192.168.20.110 LEN=52 TOS=0x10 PREC=0x00 TTL=64 ID=63704 DF PROTO=TCP SPT=60088 DPT=22 WINDOW=35 RES=0x00 ACK FIN URGP=0 UID=0 GID=0 
>>> [ 9920.235221] ipt_LOG: sk=ffff880078998000 sk->sk_socket=ffff880078c58300 file=          (null)
>>> [ 9920.235271] IN= OUT=eth1 SRC=192.168.20.108 DST=192.168.20.110 LEN=52 TOS=0x00 PREC=0x00 TTL=64 ID=0 DF PROTO=TCP SPT=60088 DPT=22 WINDOW=35 RES=0x00 ACK URGP=0 
>>>
>>> You can see in my log, that the last packet seems to be from a different
>>> socket ! (sk pointer changed to ffff880078998000 !)
>>
>> Yes, that's it.
>>
>>> Well well well, thats an ACK, in answer to FIN packet received from remote
>>> side.
>>
>> But why is it not handled by sk ffff880118bd32c0 anymore?
>> It does have, after all, the same (addr,port) tuple.
>> And it is sort of a hiccup for xt_owner users.
> 
> Its because of TIMEWAIT state : no more socket
> 
> We use a special tcp socket (net->ipv4.tcp_sock) in tcp_v4_send_ack()

Yeah, this has always been a problem with the owner match.
I don't think this fixable, it should probably only be used
in a stateful manner.
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