s390/dasd: fix null pointer dereference for ERP requests

commit 6f117cb upstream.

When requeueing all requests on the device request queue to the blocklayer
we might get to an ERP (error recovery) request that is a copy of an
original CQR.

Those requests do not have blocklayer request information or a pointer to
the dasd_queue set. When trying to access those data it will lead to a
null pointer dereference in dasd_requeue_all_requests().

Fix by checking if the request is an ERP request that can simply be
ignored. The blocklayer request will be requeued by the original CQR that
is on the device queue right behind the ERP request.

Fixes: 9487cfd ("s390/dasd: fix handling of internal requests")
Cc: <[email protected]> #4.16
Signed-off-by: Stefan Haberland <[email protected]>
Reviewed-by: Jan Hoeppner <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: Stefan Haberland

drivers/s390/block/dasd.c

@@ -2980,6 +2980,12 @@ static int _dasd_requeue_request(struct dasd_ccw_req *cqr)
 
 	if (!block)
 		return -EINVAL;
+	/*
+	 * If the request is an ERP request there is nothing to requeue.
+	 * This will be done with the remaining original request.
+	 */
+	if (cqr->refers)
+		return 0;
 	spin_lock_irq(&cqr->dq->lock);
 	req = (struct request *) cqr->callback_data;
 	blk_mq_requeue_request(req, false);