Re: [PATCH] hwrng: virtio - prevent use-after-free after a failed restore

[PrasannaKumar Muralidharan]

Hi Thorsten,

On Fri, 16 Oct 2026 at 16:16, Thorsten Blum <blum@xxxxxxxxxx> wrote:
>
> remove_common() frees the driver data during freeze, but does not clear
> vdev->priv, which points to freed memory. If probe_common() then fails
> during restore, a later remove or freeze can dereference the dangling
> pointer.
>
> Clear vdev->priv on the probe_common() error cleanup path and before
> freeing the driver data in remove_common(). Also reset the device and
> return early from remove_common() if vdev->priv is already NULL for a
> safe teardown after a failed restore.
>
> Fixes: 08e53fbdb85c ("virtio-rng: support multiple virtio-rng devices")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Thorsten Blum <blum@xxxxxxxxxx>
> ---
>  drivers/char/hw_random/virtio-rng.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/drivers/char/hw_random/virtio-rng.c b/drivers/char/hw_random/virtio-rng.c
> index 5e83ffa105e4..a9ff520975a7 100644
> --- a/drivers/char/hw_random/virtio-rng.c
> +++ b/drivers/char/hw_random/virtio-rng.c
> @@ -190,6 +190,7 @@ static int probe_common(struct virtio_device *vdev)
>  err_find:
>         ida_free(&rng_index_ida, index);
>  err_ida:
> +       vdev->priv = NULL;
>         kfree(vi);
>         return err;
>  }
> @@ -198,6 +199,11 @@ static void remove_common(struct virtio_device *vdev)
>  {
>         struct virtrng_info *vi = vdev->priv;
>
> +       if (!vi) {
> +               virtio_reset_device(vdev);
> +               return;
> +       }
> +

The virtio_reset_device() is always called before setting vdev->priv
to NULL. So the virtio device is already quiesced, no need to do early
return. Isn't it?

>         vi->hwrng_removed = true;
>         vi->data_avail = 0;
>         vi->data_idx = 0;
> @@ -207,6 +213,7 @@ static void remove_common(struct virtio_device *vdev)
>         virtio_reset_device(vdev);
>         vdev->config->del_vqs(vdev);
>         ida_free(&rng_index_ida, vi->index);
> +       vdev->priv = NULL;
>         kfree(vi);
>  }
>
>

The rest of the hunks are fine.

Thanks,
PrasannaKumar