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>

1 files changed, 11 insertions, 0 deletions

diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
index e8ab1899c88e..5c0ae90df31e 100644
--- 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