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

[Jeff Cody <jcody@redhat.com>]

On Tue, Feb 21, 2017 at 05:39:12PM +0000, Daniel P. Berrange wrote:
> On Tue, Feb 21, 2017 at 05:21:46PM +0000, Ketan Nilangekar wrote:
> > 
> > 
> > On 2/21/17, 5:59 AM, "Stefan Hajnoczi" <stefanha@gmail.com> 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 <stefanha@gmail.com> wrote:
> >     > > On Sat, Feb 18, 2017 at 12:30:31AM +0000, Ketan Nilangekar wrote:
> >     > >> On 2/17/17, 1:42 PM, "Jeff Cody" <jcody@redhat.com> 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?
> >     
> >     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).
> >     
> > [Ketan]
> > Sounds fair. Would it be ok to take this up after the driver is
> > merged for the upcoming QEMU release?
> 
> I don't think we can merge code with known security flaws, particularly
> if fixing these flaws will involve adding and/or changing command line
> parameters for the block driver.
>

We do support some protocols, such as gluster, that do not have robust
authentication frameworks over tcp/ip.  Of course, these protocols have been
in as a driver for several years (and, gluster does support unix sockets).

We seem to be establishing a rule for QEMU, that is "no new protocol drivers
without secure authentication".  That is a good thing. The existence of
current protocol drivers that don't meet that criteria is potentially
confusing for new contributors, however.  (As a side note to myself -- this
is probably a good thing to add to the wiki, if it is not there already).

I think a non-secure scheme is worse than no scheme at all, because it
becomes relied upon and promises something it cannot deliver.  In that vein,
would you object to a vxhs protocol driver that did no authentication at all
(similar to gluster), or do you think the above rule is a new hard rule for
protocol drivers?


Jeff