xhci: Add an assertion to check for virt_dev=0 bug.

During a "plug-unplug" stress test on an NEC xHCI card, a null pointer
dereference was observed.  xhci_address_device() dereferenced a null
virt_dev (possibly an erroneous udev->slot_id?); this patch adds a WARN_ON &
message to aid debug if it can be recreated.

Signed-off-by: Matt Evans <matt@ozlabs.org>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>

diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
index e8ab1899c88e03112095b170a92db428eabd42da..5c0ae90df31ec83feef099f3686dab90559fc8fe 100644 (file)
--- a/drivers/usb/host/xhci.c
+++ b/drivers/usb/host/xhci.c
@@ -2546,6 +2546,17 @@ int xhci_address_device(struct usb_hcd *hcd, struct usb_device *udev)
 
        virt_dev = xhci->devs[udev->slot_id];
 
+       if (WARN_ON(!virt_dev)) {
+               /*
+                * In plug/unplug torture test with an NEC controller,
+                * a zero-dereference was observed once due to virt_dev = 0.
+                * Print useful debug rather than crash if it is observed again!
+                */
+               xhci_warn(xhci, "Virt dev invalid for slot_id 0x%x!\n",
+                       udev->slot_id);
+               return -EINVAL;
+       }
+
        slot_ctx = xhci_get_slot_ctx(xhci, virt_dev->in_ctx);
        /*
         * If this is the first Set Address since device plug-in or