Re: CVE-2023-52466: PCI: Avoid potential out-of-bounds read in pci_dev_for_each_resource()

[Bjorn Helgaas]

On Tue, Feb 27, 2024 at 06:24:38PM +0100, Greg Kroah-Hartman wrote:
> On Tue, Feb 27, 2024 at 09:07:44AM -0600, Bjorn Helgaas wrote:
> > [+cc Mika, author of 09cc90063240]
> > 
> > On Tue, Feb 27, 2024 at 02:26:26PM +0100, Greg Kroah-Hartman wrote:
> > > On Tue, Feb 27, 2024 at 02:18:51PM +0100, Carlos López wrote:
> > > > On 25/2/24 9:16, Greg Kroah-Hartman wrote:
> > > > > There is no actual issue right now because we have another check
> > > > > afterwards and the out-of-bounds read is not being performed. In
> > > > > any case it's better code with this fixed, hence the proposed
> > > > > change.
> > > > 
> > > > Given that there is no actual security issue this looks more like a
> > > > hardening, and thus not deserving of a CVE, no?
> > > 
> > > This was a tricky one, I think it's needed as we do not know how people
> > > are really using these macros, right?  If the PCI maintainer agrees (on
> > > the cc:), I'll be glad to revoke it, it's their call.
> > 
> > 09cc90063240 ("PCI: Introduce pci_dev_for_each_resource()") added
> > pci_dev_for_each_resource(), which expands to:
> > 
> >   for (...; res = (&(dev)->resource[(bar)]), bar < PCI_NUM_RESOURCES; ...)
> > 
> > We compute "res" before the bounds-check of "bar", so the pointer may
> > be out-of-bounds, but the body of the pci_dev_for_each_resource() loop
> > is never executed with that out-of-bounds value.
> > 
> > So I don't think this is a security issue, no matter how
> > pci_dev_for_each_resource() is used, unless the mere presence of an
> > invalid address in a register is an issue.
> 
> Ah, yeah, now I remember, stuff like this was fixed up in other loops as
> just reading off into the wild can be a speculation issue and so we had
> to fix up a bunch of places in the kernel where we did have "invalid
> data" in a register.  The code didn't use that, but the processor would
> fetch from there, and boom, speculation mess.  There's a whole research
> paper published on this type of thing somewhere...
> 
> So let's keep this as a CVE unless someone really doesn't want it marked
> as such.  Again, it is a "weakness that is fixed" in the kernel, and
> because of that, a CVE can be allocated for it.

Sounds good, I'm happy to have it as a CVE.  Thanks for the
speculation details; I'm certainly not an expert on that.

Bjorn