PCI: ACPI: Check parent pointer in acpi_pci_find_companion()

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@linux.ibm.com/
Reported-by: Niklas Schnelle <schnelle@linux.ibm.com>
Tested-by: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>

diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
index 0f40943a9a18a6302c4fc8079ac391f5223dbe1a..260a06fb78a6132b27ba839b082625e4c2e44e9f 100644 (file)
--- a/drivers/pci/pci-acpi.c
+++ b/drivers/pci/pci-acpi.c
@@ -1249,6 +1249,9 @@ static struct acpi_device *acpi_pci_find_companion(struct device *dev)
        bool check_children;
        u64 addr;
 
+       if (!dev->parent)
+               return NULL;
+
        down_read(&pci_acpi_companion_lookup_sem);
 
        adev = pci_acpi_find_companion_hook ?