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

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Date:	Wed, 10 Nov 2010 06:47:17 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jan Engelhardt <jengelh@...ozas.de>
Cc:	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

Le mercredi 10 novembre 2010 à 02:09 +0100, Jan Engelhardt a écrit :
> 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 

Hmmm... skb->sk->sk_socket is really NULL ?

Are you sure its not skb->sk->sk_socket->file which is NULL ?

In this case, you might need to use sock_i_uid() / sock_i_ino() as a
fallback ? (expensive because they take a rwlock)




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