[Qemu-devel] [PATCH] virtio-serial: fix heap-over-flow

[linzhecheng]

Check device having the feature of VIRTIO_CONSOLE_F_EMERG_WRITE before
get config->emerg_wr. It is neccessary because sizeof(virtio_console_config)
is 8 byte if VirtIOSerial doesn't have the feature of
VIRTIO_CONSOLE_F_EMERG_WRITE(see virtio_serial_device_realize),
read/write emerg_wr will lead to heap-over-flow.

Signed-off-by: linzhecheng <address@hidden>

diff --git a/hw/char/virtio-serial-bus.c b/hw/char/virtio-serial-bus.c
index 9470bd7be7..3695172f37 100644
--- a/hw/char/virtio-serial-bus.c
+++ b/hw/char/virtio-serial-bus.c
@@ -580,11 +580,12 @@ static void set_config(VirtIODevice *vdev, const uint8_t 
*config_data)
     VirtIOSerial *vser = VIRTIO_SERIAL(vdev);
     struct virtio_console_config *config =
         (struct virtio_console_config *)config_data;
-    uint8_t emerg_wr_lo = le32_to_cpu(config->emerg_wr);
     VirtIOSerialPort *port = find_first_connected_console(vser);
     VirtIOSerialPortClass *vsc;
+    uint8_t emerg_wr_lo;
 
-    if (!config->emerg_wr) {
+    if (!virtio_has_feature(vser->host_features,
+        VIRTIO_CONSOLE_F_EMERG_WRITE) || !config->emerg_wr) {
         return;
     }
     /* Make sure we don't misdetect an emergency write when the guest
@@ -594,6 +595,7 @@ static void set_config(VirtIODevice *vdev, const uint8_t 
*config_data)
         return;
     }
     vsc = VIRTIO_SERIAL_PORT_GET_CLASS(port);
+    emerg_wr_lo = le32_to_cpu(config->emerg_wr);
     (void)vsc->have_data(port, &emerg_wr_lo, 1);
 }
 
-- 
2.12.2.windows.2