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Re: [Qemu-block] [PATCH v2] block: drop support for using qcow[2] encryp

From: Eric Blake
Subject: Re: [Qemu-block] [PATCH v2] block: drop support for using qcow[2] encryption with system emulators
Date: Mon, 13 Jun 2016 09:22:43 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0

On 06/13/2016 05:30 AM, Daniel P. Berrange wrote:
> Back in the 2.3.0 release we declared qcow[2] encryption as
> deprecated, warning people that it would be removed in a future
> release.

> So the safety net is correctly preventing QEMU reading cipher
> text as if it were plain text, during startup and aborting QEMU
> to avoid bad usage of this data.
> For added fun this bug only happens if the encrypted qcow2
> file happens to have data written to the first cluster,
> otherwise the cluster won't be allocated and so qcow2 would
> not try the decryption routines at all, just return all 0's.
> That no one even noticed, let alone reported, this bug that
> has shipped in 2.4.0, 2.5.0 and 2.6.0 shows that the number
> of actual users of qcow2 is approximately zero.
> So rather than fix the crash, and backport it to stable
> releases, just go ahead with what we have warned users about
> and disable any use of qcow2 encryption in the system
> emulators. qemu-img/qemu-io/qemu-nbd are still able to access
> qcow2 encrypted images for the sake of data conversion.
> In the future, qcow2 will gain support for the alternative
> luks format, but when this happens it'll be using the
> '-object secret' infrastructure for gettings keys, which


> avoids this problematic scenario entirely.
> Signed-off-by: Daniel P. Berrange <address@hidden>
> ---

Reviewed-by: Eric Blake <address@hidden>

Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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