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xhci: fix null pointer dereference on ring_doorbell_for_active_rings 

in some cases where device is attched to xhci port and do not responding,
for example ath9k_htc with stalled firmware, kernel will
crash on ring_doorbell_for_active_rings.
This patch check if pointer exist before it is used.

This patch should be backported to kernels as old as 2.6.35, that
contain the commit e9df17eb14 "USB: xhci:
Correct assumptions about number of rings per endpoint"

Signed-off-by: Oleksij Rempel <linux@rempel-privat.de>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Cc: stable@vger.kernel.org
This commit is contained in:
Oleksij Rempel 2013-07-21 15:36:19 +02:00 committed by Sarah Sharp
parent 07f3cb7c28
commit d66eaf9f89
1 changed files with 1 additions and 1 deletions
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2
drivers/usb/host/xhci-ring.c
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@ -434,7 +434,7 @@ static void ring_doorbell_for_active_rings(struct xhci_hcd *xhci,
/* A ring has pending URBs if its TD list is not empty */
if (!(ep->ep_state & EP_HAS_STREAMS)) {
if (!(list_empty(&ep->ring->td_list)))
if (ep->ring && !(list_empty(&ep->ring->td_list)))
xhci_ring_ep_doorbell(xhci, slot_id, ep_index, 0);
return;
}