ptp: ocp: fix use-after-free bugs causing by ptp_ocp_watchdog

The ptp_ocp_detach() only shuts down the watchdog timer if it is
pending. However, if the timer handler is already running, the
timer_delete_sync() is not called. This leads to race conditions
where the devlink that contains the ptp_ocp is deallocated while
the timer handler is still accessing it, resulting in use-after-free
bugs. The following details one of the race scenarios.

(thread 1)                           | (thread 2)
ptp_ocp_remove()                     |
  ptp_ocp_detach()                   | ptp_ocp_watchdog()
    if (timer_pending(&bp->watchdog))|   bp = timer_container_of()
      timer_delete_sync()            |
                                     |
  devlink_free(devlink) //free       |
                                     |   bp-> //use

Resolve this by unconditionally calling timer_delete_sync() to ensure
the timer is reliably deactivated, preventing any access after free.

Fixes: 773bda9 ("ptp: ocp: Expose various resources on the timecard.")
Signed-off-by: Duoming Zhou <[email protected]>
Reviewed-by: Vadim Fedorenko <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: stonezdm

drivers/ptp/ptp_ocp.c

@@ -4557,8 +4557,7 @@ ptp_ocp_detach(struct ptp_ocp *bp)
 	ptp_ocp_debugfs_remove_device(bp);
 	ptp_ocp_detach_sysfs(bp);
 	ptp_ocp_attr_group_del(bp);
-	if (timer_pending(&bp->watchdog))
-		timer_delete_sync(&bp->watchdog);
+	timer_delete_sync(&bp->watchdog);
 	if (bp->ts0)
 		ptp_ocp_unregister_ext(bp->ts0);
 	if (bp->ts1)