netdev - Re: [PATCH] tcp: Reject invalid ack

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Message-ID: <1350943177.8609.1383.camel@edumazet-glaptop>
Date:	Mon, 22 Oct 2012 23:59:37 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	"H.K. Jerry Chu" <hkchu@...gle.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org, ncardwell@...gle.com,
	ycheng@...gle.com
Subject: Re: [PATCH] tcp: Reject invalid ack_seq to Fast Open sockets

On Mon, 2012-10-22 at 14:26 -0700, H.K. Jerry Chu wrote:
> From: Jerry Chu <hkchu@...gle.com>
> 
> A packet with an invalid ack_seq may cause a TCP Fast Open socket to switch
> to the unexpected TCP_CLOSING state, triggering a BUG_ON kernel panic.
> 
> When a FIN packet with an invalid ack_seq# arrives at a socket in
> the TCP_FIN_WAIT1 state, rather than discarding the packet, the current
> code will accept the FIN, causing state transition to TCP_CLOSING.
> 
> This may be a small deviation from RFC793, which seems to say that the
> packet should be dropped. Unfortunately I did not expect this case for
> Fast Open hence it will trigger a BUG_ON panic.
> 
> It turns out there is really nothing bad about a TFO socket going into
> TCP_CLOSING state so I could just remove the BUG_ON statements. But after
> some thought I think it's better to treat this case like TCP_SYN_RECV
> and return a RST to the confused peer who caused the unacceptable ack_seq
> to be generated in the first place.
> 
> Signed-off-by: H.K. Jerry Chu <hkchu@...gle.com>
> Cc: Neal Cardwell <ncardwell@...gle.com>
> Cc: Yuchung Cheng <ycheng@...gle.com>
> ---

Acked-by: Eric Dumazet <edumazet@...gle.com>


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