Re: [Qemu-devel] [PATCH v8 1/2] block/vxhs.c: Add support for a new block device type called "vxhs"

[Daniel P. Berrange]

On Tue, Feb 21, 2017 at 10:59:18AM +0000, Stefan Hajnoczi wrote:
> On Mon, Feb 20, 2017 at 03:34:57AM -0800, ashish mittal wrote:
> > On Mon, Feb 20, 2017 at 3:02 AM, Stefan Hajnoczi <address@hidden> wrote:
> > > On Sat, Feb 18, 2017 at 12:30:31AM +0000, Ketan Nilangekar wrote:
> > >> On 2/17/17, 1:42 PM, "Jeff Cody" <address@hidden> wrote:
> > >>
> > >>     On Thu, Feb 16, 2017 at 02:24:19PM -0800, ashish mittal wrote:
> > >>     > Hi,
> > >>     >
> > >>     > I am getting the following error with checkpatch.pl
> > >>     >
> > >>     > ERROR: externs should be avoided in .c files
> > >>     > #78: FILE: block/vxhs.c:28:
> > >>     > +QemuUUID qemu_uuid __attribute__ ((weak));
> > >>     >
> > >>     > Is there any way to get around this, or does it mean that I would 
> > >> have
> > >>     > to add a vxhs.h just for this one entry?
> > >>     >
> > >>
> > >>     I remain skeptical on the use of the qemu_uuid as a way to select 
> > >> the TLS
> > >>     cert.
> > >>
> > >> [ketan]
> > >> Is there another identity that can be used for uniquely identifying 
> > >> instances?
> > >> The requirement was to enforce vdisk access to owner instances.
> > >
> > > The qemu_uuid weak attribute looks suspect.  What is going to provide a
> > > strong qemu_uuid symbol?
> > >
> > > Why aren't configuration parameters like the UUID coming from the QEMU
> > > command-line?
> > >
> > > Stefan
> > 
> > UUID will in fact come from the QEMU command line. VxHS is not doing
> > anything special here. It will just use the value already available to
> > qemu-kvm process.
> > 
> > QemuUUID qemu_uuid;
> > bool qemu_uuid_set;
> > 
> > Both the above are defined in vl.c. vl.c will provide the strong
> > symbol when available. There are certain binaries that do not get
> > linked with vl.c (e.g. qemu-img). The weak symbol will come into
> > affect for such binaries, and in this case, the default VXHS UUID will
> > get picked up. I had, in a previous email, explained how we plan to
> > use the default UUID. In the regular case, the VxHS controller will
> > not allow access to the default UUID (non qemu-kvm) binaries, but it
> > may choose to grant temporary access to specific vdisks for these
> > binaries depending on the workflow.
> 
> That idea sounds like a security problem.  During this time window
> anyone could use the default UUID to access the data?

Any use of the VM UUID as a means to control authorization on the
server side is a security flaw, as this is a public value which
cannot be trusted on its own.

There needs to be some kind of authentication step to verify the
reported identity, eg a password associated with the VM UUID that
is validated before trusting the VM UUID.

Alternatively there needs to be a completely separate UUID, unrelated
to the VM UUID, which is treated as a private value (eg uses the
'-object secret' framework in QEMU)

> Just make the UUID (or TLS client certificate file) a command-line
> parameter that qemu-system, qemu-img, and other tools accept (e.g.
> qemu-img via the --image-opts/--object syntax).

Regards,
Daniel
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