On Wed, Jan 10, 2018 at 06:13:22PM +0300, Edgar Kaziakhmedov wrote:
> 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 socket. But this approach
> doesn't cover scenario when socket was closed while handshaking.
> Therefore, if G_IO_IN is caught and qio_channel_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:
> 1) 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
>
> Signed-off-by: Edgar Kaziakhmedov <edgar.kaziakhme...@virtuozzo.com>
> ---
> io/channel-websock.c | 14 ++++++++++++--
> 1 file changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/io/channel-websock.c b/io/channel-websock.c
> index 87ebdebfc0..384c34b390 100644
> --- a/io/channel-websock.c
> +++ b/io/channel-websock.c
> @@ -81,6 +81,11 @@
> QIO_CHANNEL_WEBSOCK_HANDSHAKE_RES_COMMON \
> "Connection: close\r\n" \
> "\r\n"
> +#define QIO_CHANNEL_WEBSOCK_HANDSHAKE_RES_EOF \
> + "HTTP/1.1 403 Request Entity End Of File\r\n" \
> + QIO_CHANNEL_WEBSOCK_HANDSHAKE_RES_COMMON \
> + "Connection: close\r\n" \
> + "\r\n"
> #define QIO_CHANNEL_WEBSOCK_HANDSHAKE_DELIM "\r\n"
> #define QIO_CHANNEL_WEBSOCK_HANDSHAKE_END "\r\n\r\n"
> #define QIO_CHANNEL_WEBSOCK_SUPPORTED_VERSION "13"
> @@ -502,9 +507,14 @@ static int
> qio_channel_websock_handshake_read(QIOChannelWebsock *ioc,
> error_setg(errp,
> "End of headers not found in first 4096 bytes");
> return 1;
> - } else {
> - return 0;
> + } else if (ret == 0) {
> + qio_channel_websock_handshake_send_res_err(
> + ioc, QIO_CHANNEL_WEBSOCK_HANDSHAKE_RES_EOF);
> + error_setg(errp,
> + "End of headers not found before connection closed");
> + return -1;
Opps, my suggestion was slightly flawed - if we return -1, then we don't
need to call qio_channel_websock_handshake_send_res_err(), since we'll
just close the connection immediately.
Regards,
Daniel
--
|: https://berrange.com -o- https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org -o- https://fstop138.berrange.com :|
|: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
