Re: [Qemu-devel] [PATCH 1/1] io/channel-websock: handle continuous reads without any data

[Edgar Kaziakhmedov <edgar.kaziakhmedov@virtuozzo.com>]

ping


On 12/28/2017 12:36 PM, Denis V. Lunev wrote:
> From: Edgar Kaziakhmedov <edgar.kaziakhmedov@virtuozzo.com>
>
> According to the current implementation of websocket protocol in QEMU,
> qio_channel_websock_handshake_io tries to read handshake from the
> channel to start communication over tcp socket. But this subroutine
> doesn't cover scenario when socket was closed while handshaking. Therefore,
> if G_IO_IN is caught and qio_channel_websock_handshake_read returns
> zero, error has to be set and connection has to be done.
>
> Such behaviour causes 100% CPU load in main QEMU loop, because main loop
> poll continues to receive and handle G_IO_IN events from websocket.
>
> Step to reproduce 100% CPU load:
> - start qemu with the simplest configuration
>      $ qemu -vnc [::1]:1,websocket=7500
> 2) open any vnc listener (which doesn't follow websocket protocol)
>      $ vncviewer :7500
> 3) kill listener
> 4) qemu main thread eats 100% CPU usage
>
> Signed-off-by: Edgar Kaziakhmedov <edgar.kaziakhmedov@virtuozzo.com>
> Signed-off-by: Denis V. Lunev <den@openvz.org>
> CC: Daniel P. Berrange <berrange@redhat.com>
> ---
>   io/channel-websock.c | 8 +++++---
>   1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/io/channel-websock.c b/io/channel-websock.c
> index 87ebdeb..71f046a 100644
> --- a/io/channel-websock.c
> +++ b/io/channel-websock.c
> @@ -581,9 +581,11 @@ static gboolean qio_channel_websock_handshake_io(QIOChannel *ioc,
>           return FALSE;
>       }
>       if (ret == 0) {
> -        trace_qio_channel_websock_handshake_pending(ioc, G_IO_IN);
> -        /* need more data still */
> -        return TRUE;
> +        /* If G_IN_IO happened and there is no data to read, close connection */
> +        error_setg(&err, "connection was closed");
> +        qio_task_set_error(task, err);
> +        qio_task_complete(task);
> +        return FALSE;
>       }
>   
>       if (err) {