[PATCH] drm: Test for PCI root bus to avoid NULL pointer dereference

[Alex Williamson <alex.williamson@redhat.com>]

If we have a GPU on the PCI root bus that calls
drm_pcie_get_speed_cap_mask() we end up with a NULL pointer
dereference since pdev->bus->self is NULL.  We already protect
against callers passing non-PCI devices, so let's also catch this
case and return -EINVAL.

Root complex graphics are not terribly likely outside of IGD, but
when we assign a standard plugin GPU to a virtual machine, our
assumption that we have a parent device quickly becomes invalid.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
---

 drivers/gpu/drm/drm_pci.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_pci.c b/drivers/gpu/drm/drm_pci.c
index 020cfd9..411e806 100644
--- a/drivers/gpu/drm/drm_pci.c
+++ b/drivers/gpu/drm/drm_pci.c
@@ -390,7 +390,7 @@ int drm_pcie_get_speed_cap_mask(struct drm_device *dev, u32 *mask)
 	u32 lnkcap, lnkcap2;
 
 	*mask = 0;
-	if (!dev->pdev)
+	if (!dev->pdev || pci_is_root_bus(dev->pdev->bus))
 		return -EINVAL;
 
 	root = dev->pdev->bus->self;