In the Linux kernel, the following vulnerability has been resolved: virtio_console: do not free control-out buffers on remove __send_contr

In the Linux kernel, the following vulnerability has been resolved:

virtio_console: do not free control-out buffers on remove

__send_control_msg() publishes &portdev->cpkt as the control-out
virtqueue cookie. remove_vqs() walks every virtqueue and passes leftover
cookies to free_buf(), which treats them as struct port_buffer and
reads sgpages.

If a control message is still on c_ovq when the device is unbound,
free_buf() reads past the ports_device object.

KASAN reported slab-out-of-bounds in free_buf():

 1free_buf
 2remove_vqs
 3virtcons_remove
 4unbind_store

The object was the ports_device allocated in virtcons_probe().

Drain c_ovq without freeing. The packet lives in portdev and is released
with it.