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

[Philipp Stanner <phasta@mailbox.org>]

On Mon, 2025-03-10 at 08:54 +0100, Philipp Stanner wrote:
> 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".

Furthermore, I just saw that the old pcim_ code would then also be
half-broken, because it also uses PCI_STD_NUM_BARS, whereas the pci_
functions use PCI_NUM_RESOURCES:

https://elixir.bootlin.com/linux/v6.8.9/source/drivers/pci/pci.c#L6555


P.


> 
> 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
>