netdev - Re: [PATCH ipsec] xfrm: prevent ipcomp scratch buffer race condition

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Message-ID: <20131017110149.GA6747@unicorn.suse.cz>
Date:	Thu, 17 Oct 2013 13:01:49 +0200
From:	Michal Kubecek <mkubecek@...e.cz>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Steffen Klassert <steffen.klassert@...unet.com>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH ipsec] xfrm: prevent ipcomp scratch buffer race condition

On Wed, Oct 16, 2013 at 08:32:05PM +0800, Herbert Xu wrote:
> On Mon, Oct 14, 2013 at 06:03:34PM +0200, Michal Kubecek wrote:
> 
> > Add similar protection into ipcomp_decompress() as it can be
> > called from process context as well (even if such scenario seems
> > a bit artificial).
> 
> I don't think this is possible or otherwise xfrm_input will
> dead-lock.

When I was thinking about this, I came with two situations when this
might IMHO happen:

1. We are sending a packet to ourselves; this could mean not only a
local loop but also e.g. a packets between an LXC container and the host
or between two LXC containers. While it doesn't make much sense to use
compression in such case, it might happen while testing a solution which
is going to be used in a normal setup later.

2. The packet was passed to tun/tap device by a userspace application.

Am I wrong?

                                                        Michal Kubecek

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