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

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Date:	Wed, 10 Nov 2010 02:09:57 +0100 (CET)
From:	Jan Engelhardt <jengelh@...ozas.de>
To:	Netfilter Developer Mailing List <netfilter-devel@...r.kernel.org>
cc:	netdev@...r.kernel.org,
	Rafał Maj <rafal.maj.it@...il.com>
Subject: sk->sk_socket seems to disappear before connection termination

Hi,


Rafał reported this to us on IRC, paraphrasing what has been observed:

Using a simple rule like `iptables -A OUTPUT -p tcp --dport 80 -j LOG 
--log-uid`, one can observe on creating a connection and terminating
it that the trailing packets have skb->sk->sk_socket == NULL.
Is this intended? Is the socket not retained until after TCP has
sent out the closing exchange?

As I can reproduce:

$ telnet 134.76.13.21 80
Trying 134.76.13.21...
Connected to 134.76.13.21.
Escape character is '^]'.
^]
telnet> ^D
Connection closed.

[491419.500978] IN= OUT=tun0 SRC=134.76.2.163 DST=134.76.13.21 LEN=60 TOS=0x10 PREC=0x00 TTL=64 ID=35420 DF PROTO=TCP SPT=58613 DPT=80 WINDOW=5488 RES=0x00 SYN URGP=0 UID=25121 GID=100 
[491419.511533] IN= OUT=tun0 SRC=134.76.2.163 DST=134.76.13.21 LEN=52 TOS=0x10 PREC=0x00 TTL=64 ID=35421 DF PROTO=TCP SPT=58613 DPT=80 WINDOW=86 RES=0x00 ACK URGP=0 UID=25121 GID=100 
[491420.052182] IN= OUT=tun0 SRC=134.76.2.163 DST=134.76.13.21 LEN=52 TOS=0x10 PREC=0x00 TTL=64 ID=35422 DF PROTO=TCP SPT=58613 DPT=80 WINDOW=86 RES=0x00 ACK FIN URGP=0 UID=25121 GID=100 
[491420.063619] IN= OUT=tun0 SRC=134.76.2.163 DST=134.76.13.21 LEN=52 TOS=0x10 PREC=0x00 TTL=64 ID=35423 DF PROTO=TCP SPT=58613 DPT=80 WINDOW=86 RES=0x00 ACK URGP=0 
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