netdev - Re: strange tcp behavior

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Date:	Fri, 3 Aug 2007 12:21:46 +0100
From:	"Simon Arlott" <simon@...e.lp0.eu>
To:	"Evgeniy Polyakov" <johnpol@....mipt.ru>
Cc:	john@...een.lv, netdev@...r.kernel.org,
	"David Miller" <davem@...emloft.net>
Subject: Re: strange tcp behavior


On Fri, August 3, 2007 09:25, Evgeniy Polyakov wrote:
> On Thu, Aug 02, 2007 at 07:58:03PM +0100, Simon Arlott (simon@...e.lp0.eu) wrote:
>> 19:24:32.897071 IP 192.168.7.4.50000 > 192.168.7.8.2500: S 705362199:705362199(0) win 1500
>> 19:24:32.897211 IP 192.168.7.8.2500 > 192.168.7.4.50000: S 4159455228:4159455228(0) ack 705362200 win
>> 14360 <mss 7180>
>> 19:24:32.920784 IP 192.168.7.4.50000 > 192.168.7.8.2500: . ack 1 win 1500
>> 19:24:32.921732 IP 192.168.7.4.50000 > 192.168.7.8.2500: P 1:17(16) ack 1 win 1500
>> 19:24:32.921795 IP 192.168.7.8.2500 > 192.168.7.4.50000: . ack 17 win 14360
>> 19:24:32.922881 IP 192.168.7.4.50000 > 192.168.7.8.2500: R 705362216:705362216(0) win 1500
>> 19:24:34.927717 IP 192.168.7.8.2500 > 192.168.7.4.50000: R 1:1(0) ack 17 win 14360
>>
>> According to RFC 793, the RST from .4 means that the connection
>> is CLOSED.
>
> RFC 2525 - common tcp problems, says we should send RST in this case,
> although it does not specify should we send it if socket is in CLOSED
> state or not. Well, we send :)
> Even if tcp_send_active_reset() will check if socket is in CLOSED state
> and will not send data, but is still there, it will not be easily
> triggered though, but it can be possible.

Since the connection is considered closed, couldn't another socket re-use it?

Socket A: Recv data (unread)
Socket A: Recv RST
Socket B: Reuses connection (same IPs/ports)
Socket A: Close

Wouldn't that disrupt socket B's use of the connection?

-- 
Simon Arlott
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