Re: [PATCH] vfio: Fix NULL pointer dereference in vfio_pci_bus_notifier

[Kunwu Chan]

On 2024/1/12 23:30, Alex Williamson wrote:
> On Fri, 12 Jan 2024 14:22:21 +0800
> Kunwu Chan <chentao@xxxxxxxxxx> wrote:
>
> > kasprintf() returns a pointer to dynamically allocated memory
> > which can be NULL upon failure. Ensure the allocation was successful
> > by checking the pointer validity.
> >
> > Signed-off-by: Kunwu Chan <chentao@xxxxxxxxxx>
> > ---
> >   drivers/vfio/pci/vfio_pci_core.c | 2 ++
> >   1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
> > index 1cbc990d42e0..74e5b89a3a0c 100644
> > --- a/drivers/vfio/pci/vfio_pci_core.c
> > +++ b/drivers/vfio/pci/vfio_pci_core.c
> > @@ -2047,6 +2047,8 @@ static int vfio_pci_bus_notifier(struct notifier_block *nb,
> >   			 pci_name(pdev));
> >   		pdev->driver_override = kasprintf(GFP_KERNEL, "%s",
> >   						  vdev->vdev.ops->name);
> > +		if (!pdev->driver_override)
> > +			return -ENOMEM;
> >   	} else if (action == BUS_NOTIFY_BOUND_DRIVER &&
> >   		   pdev->is_virtfn && physfn == vdev->pdev) {
> >   		struct pci_driver *drv = pci_dev_driver(pdev);
>
> This is a blocking notifier callback, so errno isn't a proper return
> value, nor does it accomplish anything.  We're into the realm of
> worrying about small allocation failures here, which I understand
> essentially cannot happen, but about the best we could do at this
> point would be to WARN_ON if we weren't able to allocate an override.
Thanks for your reply.
I'll update v2 patch use WARN_ON to print some callstack msgs when we 
weren't able to allocate an override.

These msgs could reduce some of the worries and help us to find what happed.

> Thanks,
>
> Alex
--
Thanks,
  Kunwu