netdev - BSD 4.2 style TCP keepalives

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Message-Id: <20100105.163911.10233438.davem@davemloft.net>
Date:	Tue, 05 Jan 2010 16:39:11 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	netdev@...r.kernel.org
CC:	nhorman@...driver.com, ilpo.jarvinen@...sinki.fi
Subject: BSD 4.2 style TCP keepalives

To make a long story short, there are still some Windows 2000
machines out there emitting BSD 4.2 style keepalives (one garbage
byte instead of an empty out-of-window probe frame).

We don't ACK these because of how tcp_sequence() sees ->end_seq
as being equal to ->rcv_wup

But we can't change tcp_sequence() to reject these frames, because if
we do then we end up mishandling connection attempts (SYN, SYN+ACK)
and retransmits of such.

Neil has shown me a patch that does a by-hand special case of this
one-garbage-byte keepalive inside of tcp_rcv_established().

Anyone have suggestions for an alternative and perhaps cleaner
implementation of a fix?

Thanks!
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