netdev - Re: [PATCH net 1/2] ip_tunnel: Fix a memory corruption in ip_tunnel

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Message-ID: <20130926082552.GB7660@secunet.com>
Date:	Thu, 26 Sep 2013 10:25:52 +0200
From:	Steffen Klassert <steffen.klassert@...unet.com>
To:	Pravin Shelar <pshelar@...ira.com>
Cc:	David Miller <davem@...emloft.net>, netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net 1/2] ip_tunnel: Fix a memory corruption in
 ip_tunnel_xmit

On Wed, Sep 25, 2013 at 09:55:50AM -0700, Pravin Shelar wrote:
> On Tue, Sep 24, 2013 at 10:54 PM, Steffen Klassert
> <steffen.klassert@...unet.com> wrote:
> > We might extend the used aera of a skb beyond the total
> > headroom when we install the ipip header. Fix this by
> > calling skb_cow_head() unconditionally.
> >
> It is better to call skb_cow_head() from ipip_tunnel_xmit() as it is
> consistent with gre.

I think this would just move the bug from ipip to gre. ipgre_xmit()
uses dev->needed_headroom which is based on the guessed output device
in ip_tunnel_bind_dev(). If the device we get from the route lookup
in ip_tunnel_xmit() is different from the guessed one and the resulting
max_headroom is bigger than dev->needed_headroom, we run into that bug
because skb_cow_head() will not be called with the updated
dev->needed_headroom.

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