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 rxretry work (in ndostop) 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 rxretrywork.

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.