Re: [Qemu-devel] [PATCH] hw/virtio/virtio-balloon: zero-initialize the virtio_balloon_config struct

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 1/18/19 7:36 PM, Peter Maydell wrote:
> In virtio_balloon_get_config() we initialize a struct virtio_balloon_config
> which we then copy to guest memory. However, the local variable is not
> zero initialized. This works OK at the moment because we initialize
> all the fields in it; however an upcoming kernel header change will
> add some new fields. If we don't zero out the whole struct then we
> will start leaking a small amount of the contents of QEMU's stack
> to the guest as soon as we update linux-headers/ to a set of headers
> that includes the new fields.

Is it worth Cc'ing qemu-stable@?

> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>

> ---
> It looks like none of the other virtio devices have this bug.
> Tested with "make check" only.
> As the commit message notes, must go in before our next headers update.
> ---
>  hw/virtio/virtio-balloon.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
> index 1728e4f83af..a12677d4d5b 100644
> --- a/hw/virtio/virtio-balloon.c
> +++ b/hw/virtio/virtio-balloon.c
> @@ -311,7 +311,7 @@ out:
>  static void virtio_balloon_get_config(VirtIODevice *vdev, uint8_t *config_data)
>  {
>      VirtIOBalloon *dev = VIRTIO_BALLOON(vdev);
> -    struct virtio_balloon_config config;
> +    struct virtio_balloon_config config = {};
>  
>      config.num_pages = cpu_to_le32(dev->num_pages);
>      config.actual = cpu_to_le32(dev->actual);
>