netdev - Re: [PATCH 3/3] [PPP] L2TP: Fix skb handling in pppol2tp

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Date:	Tue, 18 Sep 2007 21:19:33 +0100
From:	James Chapman <jchapman@...alix.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
CC:	"David S. Miller" <davem@...emloft.net>,
	Michal Ostrowski <mostrows@...akeasy.net>,
	Paul Mackerras <paulus@...ba.org>,
	Toralf Förster <toralf.foerster@....de>,
	netdev@...r.kernel.org
Subject: Re: [PATCH 3/3] [PPP] L2TP: Fix skb handling in pppol2tp_xmit

Herbert Xu wrote:
> [PPP] L2TP: Fix skb handling in pppol2tp_xmit
> 
> This patch makes pppol2tp_xmit call skb_cow_head so that we don't modify
> cloned skb data.  It also gets rid of skb2 we only need to preserve the
> original skb for congestion notification, which is only applicable for
> ppp_async and ppp_sync.
> 
> The other semantic change made here is the removal of socket accounting
> for data tranmitted out of pppol2tp_xmit.  The original code leaked any
> existing socket skb accounting.  We could fix this by dropping the
> original skb owner.  However, this is undesirable as the packet has not
> physically left the host yet.
> 
> In fact, all other tunnels in the kernel do not account skb's passing
> through to their own socket.  In partciular, ESP over UDP does not do
> so and it is the closest tunnel type to PPPoL2TP.  So this patch simply
> removes the socket accounting in pppol2tp_xmit.  The accounting still
> applies to control packets of course.
> 
> I've also added a reminder that the outgoing checksum here doesn't work.
> I suppose existing deployments don't actually enable checksums.
> 
> Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>

This one causes my test system to lock up. I'll investigate. Please 
don't apply this patch for now.

-- 
James Chapman
Katalix Systems Ltd
http://www.katalix.com
Catalysts for your Embedded Linux software development

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