vsock/virtio: initialize the_virtio_vsock before using VQs

Once VQs are filled with empty buffers and we kick the host, it can send
connection requests. If the_virtio_vsock is not initialized before,
replies are silently dropped and do not reach the host.

virtio_transport_send_pkt() can queue packets once the_virtio_vsock is
set, but they won't be processed until vsock->tx_run is set to true. We
queue vsock->send_pkt_work when initialization finishes to send those
packets queued earlier.

Fixes: 0deab087 ("vsock/virtio: use RCU to avoid use-after-free on the_virtio_vsock")
Signed-off-by: Alexandru Matei <alexandru.matei@uipath.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Link: https://lore.kernel.org/r/20231024191742.14259-1-alexandru.matei@uipath.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/vmw_vsock/virtio_transport.c

@@ -555,6 +555,11 @@ static int virtio_vsock_vqs_init(struct virtio_vsock *vsock)
 
 	virtio_device_ready(vdev);
 
+	return 0;
+}
+
+static void virtio_vsock_vqs_start(struct virtio_vsock *vsock)
+{
 	mutex_lock(&vsock->tx_lock);
 	vsock->tx_run = true;
 	mutex_unlock(&vsock->tx_lock);
@@ -569,7 +574,16 @@ static int virtio_vsock_vqs_init(struct virtio_vsock *vsock)
 	vsock->event_run = true;
 	mutex_unlock(&vsock->event_lock);
 
-	return 0;
+	/* virtio_transport_send_pkt() can queue packets once
+	 * the_virtio_vsock is set, but they won't be processed until
+	 * vsock->tx_run is set to true. We queue vsock->send_pkt_work
+	 * when initialization finishes to send those packets queued
+	 * earlier.
+	 * We don't need to queue the other workers (rx, event) because
+	 * as long as we don't fill the queues with empty buffers, the
+	 * host can't send us any notification.
+	 */
+	queue_work(virtio_vsock_workqueue, &vsock->send_pkt_work);
 }
 
 static void virtio_vsock_vqs_del(struct virtio_vsock *vsock)
@@ -664,6 +678,7 @@ static int virtio_vsock_probe(struct virtio_device *vdev)
 		goto out;
 
 	rcu_assign_pointer(the_virtio_vsock, vsock);
+	virtio_vsock_vqs_start(vsock);
 
 	mutex_unlock(&the_virtio_vsock_mutex);
 
@@ -736,6 +751,7 @@ static int virtio_vsock_restore(struct virtio_device *vdev)
 		goto out;
 
 	rcu_assign_pointer(the_virtio_vsock, vsock);
+	virtio_vsock_vqs_start(vsock);
 
 out:
 	mutex_unlock(&the_virtio_vsock_mutex);