Re: [PATCH] PCI: ACPI: Check parent pointer in acpi_pci_find_companion()

[Bjorn Helgaas]

On Fri, Oct 01, 2021 at 03:58:10PM +0200, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> 
> If acpi_pci_find_companion() is called for a device whose parent
> pointer is NULL, it will crash when attempting to get the ACPI
> companion of the parent due to a NULL pointer dereference in
> the ACPI_COMPANION() macro.
> 
> This was not a problem before commit 375553a93201 ("PCI: Setup ACPI
> fwnode early and at the same time with OF") that made pci_setup_device()
> call pci_set_acpi_fwnode() and so it allowed devices with NULL parent
> pointers to be passed to acpi_pci_find_companion() which is the case
> in pci_iov_add_virtfn(), for instance.
> 
> Fix this issue by making acpi_pci_find_companion() check the device's
> parent pointer upfront and bail out if it is NULL.
> 
> While pci_iov_add_virtfn() can be changed to set the device's parent
> pointer before calling pci_setup_device() for it, checking pointers
> against NULL before dereferencing them is prudent anyway and looking
> for ACPI companions of virtual functions isn't really useful.
> 
> Fixes: 375553a93201 ("PCI: Setup ACPI fwnode early and at the same time with OF")
> Link: https://lore.kernel.org/linux-acpi/8e4bbd5c59de31db71f718556654c0aa077df03d.camel@xxxxxxxxxxxxx/
> Reported-by: Niklas Schnelle <schnelle@xxxxxxxxxxxxx>
> Tested-by: Niklas Schnelle <schnelle@xxxxxxxxxxxxx>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>

Acked-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>

> ---
>  drivers/pci/pci-acpi.c |    3 +++
>  1 file changed, 3 insertions(+)
> 
> Index: linux-pm/drivers/pci/pci-acpi.c
> ===================================================================
> --- linux-pm.orig/drivers/pci/pci-acpi.c
> +++ linux-pm/drivers/pci/pci-acpi.c
> @@ -1243,6 +1243,9 @@ static struct acpi_device *acpi_pci_find
>  	bool check_children;
>  	u64 addr;
>  
> +	if (!dev->parent)
> +		return NULL;
> +
>  	down_read(&pci_acpi_companion_lookup_sem);
>  
>  	adev = pci_acpi_find_companion_hook ?
> 
> 
>