From: Denis V. Lunev <den@openvz.org> qio_channel_websock_handshake_send() treats every negative return from qio_channel_write() as fatal and passes err to error_get_pretty(). QIO_CHANNEL_ERR_BLOCK is negative but leaves err NULL, so a socket which cannot take the response immediately crashes QEMU before the client has authenticated. Keep the G_IO_OUT watch armed and retry instead. Fixes: 2d1d0e70cf3e ("io: add QIOChannelWebsock class") Fixes: CVE-2026-84788 Cc: qemu-stable@nongnu.org Cc: Daniel P. Berrangé <berrange@redhat.com> Cc: Marc-André Lureau <marcandre.lureau@redhat.com> Reviewed-by: Daniel P. Berrangé <berrange@redhat.com> Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com> Signed-off-by: Denis V. Lunev <den@openvz.org> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com> --- io/channel-websock.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/io/channel-websock.c b/io/channel-websock.c index 66c91ed2a2..8f27b1f12b 100644 --- a/io/channel-websock.c +++ b/io/channel-websock.c @@ -562,6 +562,11 @@ static gboolean qio_channel_websock_handshake_send(QIOChannel *ioc, wioc->encoutput.offset, &err); + if (ret == QIO_CHANNEL_ERR_BLOCK) { + /* Socket buffer is full, the G_IO_OUT watch stays armed */ + return TRUE; + } + if (ret < 0) { trace_qio_channel_websock_handshake_fail(ioc, error_get_pretty(err)); qio_task_set_error(task, err); -- 2.55.0