Re: [PATCH] acpi: validate hotplug selector on access

[Michael S. Tsirkin]

On Thu, Dec 23, 2021 at 10:58:14AM +0100, Mauro Matteo Cascella wrote:
> Hi,
> 
> On Wed, Dec 22, 2021 at 9:52 PM Michael S. Tsirkin <mst@redhat.com> wrote:
> >
> > On Wed, Dec 22, 2021 at 09:27:51PM +0100, Philippe Mathieu-Daudé wrote:
> > > On Wed, Dec 22, 2021 at 9:20 PM Michael S. Tsirkin <mst@redhat.com> wrote:
> > > > On Wed, Dec 22, 2021 at 08:19:41PM +0100, Philippe Mathieu-Daudé wrote:
> > > > > +Mauro & Alex
> > > > >
> > > > > On 12/21/21 15:48, Michael S. Tsirkin wrote:
> > > > > > When bus is looked up on a pci write, we didn't
> > > > > > validate that the lookup succeeded.
> > > > > > Fuzzers thus can trigger QEMU crash by dereferencing the NULL
> > > > > > bus pointer.
> > > > > >
> > > > > > Fixes: b32bd763a1 ("pci: introduce acpi-index property for PCI 
> > > > > > device")
> > > > > > Cc: "Igor Mammedov" <imammedo@redhat.com>
> > > > > > Fixes: https://gitlab.com/qemu-project/qemu/-/issues/770
> > > > > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > > > >
> > > > > It seems this problem is important enough to get a CVE assigned.
> > > >
> > > > Guest root can crash guest.
> > > > I don't see why we would assign a CVE.
> > >
> > > Well thinking about downstream distributions, if there is a CVE assigned,
> > > it helps them to have it written in the commit. Maybe I am mistaken.
> > >
> > > Unrelated but it seems there is a coordination problem with the
> > > qemu-security@ list,
> > > if this isn't a security issue, why was a CVE requested?
> >
> > Right.  I don't think a priveleged user crashing VM warrants a CVE,
> > it can just halt a CPU or whatever. Just cancel the CVE request pls.
> 
> While I agree with you that this is kind of borderline and I expressed
> similar concerns in the past, I was told that:
> 
> 1) root guest users are not necessarily trustworthy (from the host 
> perspective).
> 2) NULL pointer deref and similar issues caused by an
> ill-handled/error condition are CVE worthy, even if triggered by root.
> 3) In other cases, DoS triggered by root is not a security issue
> because it's an expected behavior and not an ill-handled/error
> condition (think of assert failures, for example).
> 
> In other words, "ill-handled condition" is the crucial factor that
> makes a bug CVE worthy or not.

I guess the point is that a downstream might have a slightly different
code path where it would be more serious ...
OK then, not a big deal for me. So what's the CVE # then?

> +Prasad, can you shed some light on this? Is my understanding correct?
> 
> Also, please note that we regularly get CVE requests for bugs like
> this and many CVEs have been assigned in the past. Of course that
> doesn't mean we can't change things going forward, but I think we
> should make it clear (probably here:
> https://www.qemu.org/docs/master/system/security.html) that these
> kinds of bugs are not eligible for CVE assignment.


That would be good, yes.

> > > > > Mauro, please update us when you get the CVE number.
> > > > > Michael, please amend the CVE number before committing the fix.
> > > > >
> > > > > FWIW Paolo asked every fuzzed bug reproducer to be committed
> > > > > as qtest, see tests/qtest/fuzz*c. Alex has a way to generate
> > > > > reproducer in plain C.
> > > > >
> > > > > Regards,
> > > > >
> > > > > Phil.
> > > >
> >
> 
> -- 
> Mauro Matteo Cascella
> Red Hat Product Security
> PGP-Key ID: BB3410B0