TCP zombie connections with 7-RELEASE and STABLE from 15th june

[Mike Silbersack]

On Fri, 18 Jul 2008, Bernd Walter wrote:

> 443 is a self written server, but it also happens with port 80 and
> sslproxy.
> The client is a telnet, which disconnects directly after connecting,
> so the disconnect is initiated from the client, which seems to be
> important for this problem to trigger.
>
> You can see that the FIN handshake completes and netstat on the
> client box shows the connection in TIME_WAIT.
> The server however has the connection still in ESTABLISHED state.

Well, syncookies allow the ack of the 3WHS to establish a connection. 
Just a quick look at your tcpdump shows that since you aren't sending any 
data you are not advancing the sequence number.  As a result, it looks 
like one of the ACKs the client sends during connection shutdown may 
actually be causing the server to re-establish the connection.

You might want to file a PR with exact instructions (and code) that'll 
easily reproduce this so that it can be solved at some point in the 
future.  I don't have time to look into it now, although I'd be happy to 
code review a fix!

-Mike