CVE-2026-63874

In the Linux kernel, the following vulnerability has been resolved:

net: mctp: usb: fix race between urb completion and rx_retry cancellation

It's possible that sequencing between setting ->stopped and cancelling
the rx_retry work (in ndo_stop) could leave us with an urb queued:

    T1: ndo_stop                  T2: rx_retry_work
    ------------                  ----------------
                                  LD: ->stopped => false
    ST: ->stopped <= true
    usb_kill_urb()
                                  mctp_usb_rx_queue()
                                    usb_submit_urb()
    cancel_delayed_work_sync()

That urb completion can then re-schedule rx_retry_work.

Strenghen the sequencing between the stop (preventing another requeue)
and the cancel by updating both atomically under a new rx lock. After
setting ->rx_stopped, and cancelling pending work, we know that the
requeue cannot occur, so all that's left is killing any pending urb.