vsock/virtio: add WARN_ON check on virtio_transport_get_ops()

virtio_transport_get_ops() and virtio_transport_send_pkt_info()
can only be used on connecting/connected sockets, since a socket
assigned to a transport is required.

This patch adds a WARN_ON() on virtio_transport_get_ops() to check
this requirement, a comment and a returned error on
virtio_transport_send_pkt_info(),
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/vmw_vsock/virtio_transport_common.c

@@ -34,6 +34,9 @@ virtio_transport_get_ops(struct vsock_sock *vsk)
 {
 	const struct vsock_transport *t = vsock_core_get_transport(vsk);
 
+	if (WARN_ON(!t))
+		return NULL;
+
 	return container_of(t, struct virtio_transport, transport);
 }
 
@@ -161,15 +164,25 @@ void virtio_transport_deliver_tap_pkt(struct virtio_vsock_pkt *pkt)
 }
 EXPORT_SYMBOL_GPL(virtio_transport_deliver_tap_pkt);
 
+/* This function can only be used on connecting/connected sockets,
+ * since a socket assigned to a transport is required.
+ *
+ * Do not use on listener sockets!
+ */
 static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
 					  struct virtio_vsock_pkt_info *info)
 {
 	u32 src_cid, src_port, dst_cid, dst_port;
+	const struct virtio_transport *t_ops;
 	struct virtio_vsock_sock *vvs;
 	struct virtio_vsock_pkt *pkt;
 	u32 pkt_len = info->pkt_len;
 
-	src_cid = virtio_transport_get_ops(vsk)->transport.get_local_cid();
+	t_ops = virtio_transport_get_ops(vsk);
+	if (unlikely(!t_ops))
+		return -EFAULT;
+
+	src_cid = t_ops->transport.get_local_cid();
 	src_port = vsk->local_addr.svm_port;
 	if (!info->remote_cid) {
 		dst_cid	= vsk->remote_addr.svm_cid;
@@ -202,7 +215,7 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
 
 	virtio_transport_inc_tx_pkt(vvs, pkt);
 
-	return virtio_transport_get_ops(vsk)->send_pkt(pkt);
+	return t_ops->send_pkt(pkt);
 }
 
 static bool virtio_transport_inc_rx_pkt(struct virtio_vsock_sock *vvs,