Re: [PATCH v3 9/9] pci: fix UAF when probe runs concurrent to dyn ID removal

[Bjorn Helgaas <helgaas@kernel.org>]

On Thu, Jul 23, 2026 at 07:57:58PM +0100, Gary Guo wrote:
> On Tue Jul 21, 2026 at 11:35 PM BST, Bjorn Helgaas wrote:
> > On Mon, Jul 06, 2026 at 03:11:21PM +0100, Gary Guo wrote:
> >> Dynamic IDs are only guaranteed to be valid when dynids.lock is held,
> >> as remove_id_store can free the node. Thus, make a copy in
> >> pci_match_device. Also, clarify that the id parameter is only valid during
> >> probe.
> >> 
> >> Reported-by: Sashiko <sashiko-bot@kernel.org>
> >> Link: https://lore.kernel.org/all/20260619170503.518F61F00A3A@smtp.kernel.org/
> >> Fixes: 0994375e9614 ("PCI: add remove_id sysfs entry")
> >> Signed-off-by: Gary Guo <gary@garyguo.net>
> >> ---
> >>  drivers/pci/pci-driver.c | 28 +++++++++++++++-------------
> >>  include/linux/pci.h      |  1 +
> >>  2 files changed, 16 insertions(+), 13 deletions(-)
> >> 
> >> diff --git a/include/linux/pci.h b/include/linux/pci.h
> >> index 64b308b6e61c..92c17c116de6 100644
> >> --- a/include/linux/pci.h
> >> +++ b/include/linux/pci.h
> >> @@ -979,6 +979,7 @@ struct module;
> >>   *		function returns zero when the driver chooses to
> >>   *		take "ownership" of the device or an error code
> >>   *		(negative number) otherwise.
> >> + *		The pci_device_id parameter is only valid during probe.
> >
> > The probe function takes a pointer to a struct pci_device_id, so I
> > think the requirement is that the struct pci_device_id only *needs* to
> > be valid during .probe(), right, i.e., the PCI core probe path makes
> > its own copy of the ID and doesn't retain the pointer after .probe()
> > returns, right?
> >
> > I assume the caller determines the struct pci_device_id lifetime, and
> > it could be forever.
> >
> > Could say something like:
> >
> >   The pci_device_id parameter only needs to be valid during probe.
> 
> As a contract on function parameter, the caller needs to guarantee that it lives
> at least as long as documented (i.e. during the whole probe) and the callee
> cannot assume that it will be valid beyond what's guaranteed.
> 
> How about:
> 
>     The pci_device_id parameter is only guaranteed to be valid during probe.

That's ok with me.  My only niggle is that this documentation is that the
*consumer* end, and of course the consumer, i.e., the PCI core probe path,
can't guarantee anything about the parameters it receives.  But I guess
your point is that the *caller* must guarantee that the parameter remains
valid during probe.

The only thing the consumer can guarantee is that it doesn't depend on the
pci_device_id parameter after the probe returns.