Check event delay function before calling it

If no event handler has been set or an event handler has been removed,
the delay function will be NULL. Nevertheless, events may still be sent
by the EC (whether configured to do so or not), so we need to check the
delay function and ensure it is non-NULL before calling it.

In case it is NULL, we assume a delay of zero, forwarding it to the
workq-queue and let the work function take care of logging it as
unhandled event.

Reported by: Blaž Hrastnik <blaz@mxxn.io>

Author: qzed

module/surface_sam_ssh.c

@@ -909,7 +909,7 @@ static void ssh_handle_event(struct sam_ssh_ec *ec, const u8 *buf)
 
 	surface_sam_ssh_event_handler_delay delay_fn;
 	void *handler_data;
-	unsigned long delay = 0;
+	unsigned long delay;
 
 	ctrl = (const struct ssh_frame_ctrl *)(buf + SSH_FRAME_OFFS_CTRL);
 	cmd  = (const struct ssh_frame_cmd  *)(buf + SSH_FRAME_OFFS_CMD);
@@ -945,7 +945,12 @@ static void ssh_handle_event(struct sam_ssh_ec *ec, const u8 *buf)
 	spin_lock_irqsave(&ec->events.lock, flags);
 	handler_data = ec->events.handler[work->event.rqid - 1].data;
 	delay_fn = ec->events.handler[work->event.rqid - 1].delay;
-	delay = delay_fn(&work->event, handler_data);
+
+	/* Note:
+	 * We need to check delay_fn here: This may have never been set as we
+	 * can't guarantee that events only occur when they have been enabled.
+	 */
+	delay = delay_fn ? delay_fn(&work->event, handler_data) : 0;
 	spin_unlock_irqrestore(&ec->events.lock, flags);
 
 	// immediate execution for high priority events (e.g. keyboard)