From: Michal Pecio michal.pecio@gmail.com
This check is performed before prepare_transfer() and prepare_ring(), so enqueue can already point at the final link TRB of a segment. And indeed it will, some 0.4% of times this code is called.
Then enqueue + 1 is an invalid pointer. It will crash the kernel right away or load some junk which may look like a link TRB and cause the real link TRB to be replaced with a NOOP. This wouldn't end well.
Use a functionally equivalent test which doesn't dereference the pointer and always gives correct result.
Something has crashed my machine twice in recent days while playing with an Etron HC, and a control transfer stress test ran for confirmation has just crashed it again. The same test passes with this patch applied.
Fixes: 5e1c67abc930 ("xhci: Fix control transfer error on Etron xHCI host") Cc: stable@vger.kernel.org Signed-off-by: Michal Pecio michal.pecio@gmail.com Signed-off-by: Mathias Nyman mathias.nyman@linux.intel.com --- drivers/usb/host/xhci-ring.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c index 4e975caca235..b906bc2eea5f 100644 --- a/drivers/usb/host/xhci-ring.c +++ b/drivers/usb/host/xhci-ring.c @@ -3777,7 +3777,7 @@ int xhci_queue_ctrl_tx(struct xhci_hcd *xhci, gfp_t mem_flags, * enqueue a No Op TRB, this can prevent the Setup and Data Stage * TRB to be breaked by the Link TRB. */ - if (trb_is_link(ep_ring->enqueue + 1)) { + if (last_trb_on_seg(ep_ring->enq_seg, ep_ring->enqueue + 1)) { field = TRB_TYPE(TRB_TR_NOOP) | ep_ring->cycle_state; queue_trb(xhci, ep_ring, false, 0, 0, TRB_INTR_TARGET(0), field);