netdev - Re: [PATCH] L2TP: avoid skb truesize bug if headroom is increased

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Message-Id: <20080519.141038.267900372.davem@davemloft.net>
Date:	Mon, 19 May 2008 14:10:38 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	jchapman@...alix.com
Cc:	netdev@...r.kernel.org, bc-info@...x.cabel.net
Subject: Re: [PATCH] L2TP: avoid skb truesize bug if headroom is increased

From: James Chapman <jchapman@...alix.com>
Date: Mon, 19 May 2008 21:09:08 +0100

> A user reported seeing occasional bugs such as the following when
> using the L2TP driver.
> 
>   SKB BUG: Invalid truesize (272) len=72, sizeof(sk_buff)=208
> 
> When L2TP adds its header in the transmit path, it might need to
> increase the headroom of the skb. In some cases, the increased
> headroom trips a kernel bug when the skb is freed because the skb has
> grown beyond its truesize value. The fix is to increase the truesize
> by the amount of headroom added, after orphaning the skb.
> 
> While here, fix a misleading comment.
> 
> Thanks to Iouri Kharon <bc-info@...x.cabel.net> for the initial
> report and testing the fix.
> 
> Signed-off-by: James Chapman <jchapman@...alix.com>

Applied, thanks James.

Longer term I'll try to come up with a way to make it harder
to get this stuff wrong.
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