linux-kernel - Re: [BUG] SNAT sometimes allows packets to pass through unchanged

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Message-ID: <Pine.LNX.4.44L0.0902121008050.2388-100000@iolanthe.rowland.org>
Date:	Thu, 12 Feb 2009 10:11:32 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Patrick McHardy <kaber@...sh.net>
cc:	netdev@...r.kernel.org,
	Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: [BUG] SNAT sometimes allows packets to pass through unchanged

On Thu, 12 Feb 2009, Patrick McHardy wrote:

> If the connection has already timed out (from conntracks perspective),
> it has lost its state. Unless connection pickup is enabled, the packet 
> will be marked as INVALID because it doesn't belong to a connection.
> You can control dropping of these packets yourself by adding the
> appropriate "-m state --state INVALID" rules.

I tried adding a rule to log these unaccounted-for packets.  Nothing 
showed up, even when I could see the packets being sent.

> That said, there were
> some bugs in the past few releases that caused some bad interaction
> between TCP and TCP conntrack (not sure anymore which one of both was
> to blame). Its possible that this is the root cause for this, so
> you might want to consider a kernel update.

It does sound like the result of a bug.  Do you have any pointers to 
patches or locations to check in the source?

Alan Stern

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