rdma_cm: fail iwarp accepts w/o connection params

cma_accept_iw() needs to return an error if conn_params is NULL.
Since this is coming from user space, we can crash.

Reported-by: Shaobo He <shaobo@cs.utah.edu>
Acked-by: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Steve Wise <swise@opengridcomputing.com>
Cc: stable@vger.kernel.org
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/core/cma.c

@@ -3683,6 +3683,9 @@ static int cma_accept_iw(struct rdma_id_private *id_priv,
 	struct iw_cm_conn_param iw_param;
 	int ret;
 
+	if (!conn_param)
+		return -EINVAL;
+
 	ret = cma_modify_qp_rtr(id_priv, conn_param);
 	if (ret)
 		return ret;