nvme-fc: Prevent null pointer dereference in nvme_fc_io_getuuid()

The nvme_fc_fcp_op structure describing an AEN operation is initialized with a
null request structure pointer. An FC LLDD may make a call to
nvme_fc_io_getuuid passing a pointer to an nvmefc_fcp_req for an AEN operation.

Add validation of the request structure pointer before dereference.
Signed-off-by: Nigel Kirkland <nkirkland2304@gmail.com>
Reviewed-by: James Smart <jsmart2021@gmail.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>

drivers/nvme/host/fc.c

@@ -1924,7 +1924,7 @@ char *nvme_fc_io_getuuid(struct nvmefc_fcp_req *req)
 	struct nvme_fc_fcp_op *op = fcp_req_to_fcp_op(req);
 	struct request *rq = op->rq;
 
-	if (!IS_ENABLED(CONFIG_BLK_CGROUP_FC_APPID) || !rq->bio)
+	if (!IS_ENABLED(CONFIG_BLK_CGROUP_FC_APPID) || !rq || !rq->bio)
 		return NULL;
 	return blkcg_get_fc_appid(rq->bio);
 }