Re: [bug report] PCI: Check BAR index for validity

[Philipp Stanner <phasta@mailbox.org>]

On Sat, 2025-03-08 at 15:07 -0600, Bjorn Helgaas wrote:
> On Sat, Mar 08, 2025 at 01:23:28PM +0300, Dan Carpenter wrote:
> > Hello Philipp Stanner,
> > 
> > Commit ba10e5011d05 ("PCI: Check BAR index for validity") from Mar
> > 4,
> > 2025 (linux-next), leads to the following Smatch static checker
> > warning:
> > 
> > 	drivers/pci/devres.c:632
> > pcim_remove_bar_from_legacy_table()
> > 	error: buffer overflow 'legacy_iomap_table' 6 <= 15
> 
> Thanks, I dropped this patch for now.
> 
> > drivers/pci/devres.c
> >     621 static void pcim_remove_bar_from_legacy_table(struct
> > pci_dev *pdev, int bar)
> >     622 {
> >     623         void __iomem **legacy_iomap_table;
> >     624 
> >     625         if (!pci_bar_index_is_valid(bar))
> > 
> > This line used to check PCI_STD_NUM_BARS (6) but now it's checking
> > PCI_NUM_RESOURCES (15).

What is even going on here. Why are thos different values? Does a PCI
device now have at most 6, or 15 BARs?

Or is a BAR different from a "resource"?

And why would it be 15? I haven't read the standard, but I would
suspect it should be 16.

And which of those two here should be used?
https://elixir.bootlin.com/linux/v6.14-rc4/source/include/linux/pci.h#L133

The comment doesn't say *which one* is "preserved for backwards
compatibility".

So many questions…

But granted, the check is wrong for the devres resource array, and I
suppose it should be made the same size as pci_dev.resource.


> > 
> >     626                 return;
> >     627 
> >     628         legacy_iomap_table = (void __iomem
> > **)pcim_iomap_table(pdev);
> >     629         if (!legacy_iomap_table)
> >     630                 return;
> >     631 
> > --> 632         legacy_iomap_table[bar] = NULL;
> >                 ^^^^^^^^^^^^^^^^^^^^^^^
> > Leading to a buffer overflow.

Leading to a *potential* buffer overflow.

Anyways, thanks for reporting.

P.


> > 
> >     633 }
> > 
> > regards,
> > dan carpenter