linux-kernel - Re: [RFC/GIT PULL] Linux KVM tool for v3.2

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Date:	Thu, 10 Nov 2011 10:21:57 +0200
From:	Pekka Enberg <penberg@...nel.org>
To:	Markus Armbruster <armbru@...hat.com>
Cc:	Anthony Liguori <anthony@...emonkey.ws>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Avi Kivity <avi@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, Christoph Hellwig <hch@....de>
Subject: Re: [RFC/GIT PULL] Linux KVM tool for v3.2

On Thu, Nov 10, 2011 at 9:57 AM, Markus Armbruster <armbru@...hat.com> wrote:
>>> 3) The block probing code replicates a well known CVE from three
>>> years ago[1]. Using kvm-tool, a malicious guest could write the
>>> qcow2 signature to the zero sector and use that to attack the host.
>>
>> We don't support QCOW2 snapshots so I don't see how the "arbitrary
>> file" thing can happen.
>
> You don't need snapshots for the hole.
>
> Start with a clean read/write raw image.  Probing declares it raw.
> Guest writes QCOW signature to it, with a backing file of its choice.
>
> Restart with the same image.  Probing declares it QCOW2.  Guest can read
> the backing file.  Oops.
>
> Probing images works when all image types can be probed reliably, and
> the guest can't mess with the probing.  Requires distinctive signatures
> the guest can't change.  Raw images spoil it.

We don't support that "backing file" thing either. ;-)

On Thu, Nov 10, 2011 at 9:57 AM, Markus Armbruster <armbru@...hat.com> wrote:
>> It's pretty sad though that we're replicating a known security issue :-/
>
> Maybe I'm wrong, but I got the impression you've been replicating quite
> a few of QEMU's early mistakes.
>
> I hope you can create something better than QEMU, I really, really do.
> But to successfully build a second system, you need to learn the right
> lessons from the first system.  Are you sure you do?

We do but it's a fair question if we're doing it enough. I don't have
a simple answer to that.

                        Pekka
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