Messages in this thread | | | Date | Tue, 27 Feb 2024 09:07:44 -0600 | From | Bjorn Helgaas <> | Subject | Re: CVE-2023-52466: PCI: Avoid potential out-of-bounds read in pci_dev_for_each_resource() |
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[+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.
The same address computation is used for "pci_resource_start(dev, bar)", which is used in hundreds of places where drivers supply the BAR index, and the index is not checked.
We could consider adding a bounds check in pci_resource_n() to turn a potential out-of-bounds reference into a NULL pointer dereference, e.g.,
#define pci_resource_n(dev, bar) (bar < PCI_NUM_RESOURCES ? &(dev)->resource[(bar)] : NULL)
But of course, there's nothing stopping drivers from computing "&dev->resource[junk]" themselves.
Bjorn
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