Executive brief
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():
free_buf remove_vqs virtcons_remove unbind_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.