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Date: Fri, 13 Dec 2013 04:07:11 +0100
From: Hannes Frederic Sowa <hannes@stressinduktion.org>
To: Eric Dumazet <eric.dumazet@gmail.com>,
        Christian Grothoff <grothoff@in.tum.de>,
        Jacob Appelbaum <jacob@appelbaum.net>,
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        David Miller <davem@davemloft.net>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, knock@gnunet.org
Subject: Re: [PATCH] TCP: add option for silent port knocking with integrity protection
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On Thu, Dec 12, 2013 at 04:46:37PM +0100, Hannes Frederic Sowa wrote:
> On Thu, Dec 12, 2013 at 06:34:24AM -0800, Eric Dumazet wrote:
> > With various proposals (like TCP minion), maybe its time to be able to
> > implement part of TCP stack in user land (Keep the mux inside the
> > kernel, and forward raw incoming packets to user land where all the
> > crazy things can be done without kernel patching.)
> 
> Maybe this knocking scheme is implementable with a socket filter and we could
> add a switch to tweak drop behaviour.

Just fyi, maybe it is useful. I haven't tested it:

For the sending side one could craft the handshake by hand (raw/packet
sockets) and splice in an already established socket via tcp connection
repair.