Re: [PATCH v2] virtio: fix reference leak in register_virtio_device()

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Dec 18, 2024 at 11:12:01AM +0800, Ma Ke wrote:
> Once device_add(&dev->dev) failed, call put_device() to explicitly
> release dev->dev. Or it could cause double free problem.
> 
> As comment of device_add() says, 'if device_add() succeeds, you should
> call device_del() when you want to get rid of it. If device_add() has
> not succeeded, use only put_device() to drop the reference count'.
> 
> Found by code review.
> 
> Cc: stable@vger.kernel.org
> Fixes: f2b44cde7e16 ("virtio: split device_register into device_initialize and device_add")
> Signed-off-by: Ma Ke <make_ruc2021@163.com>


Did you actually test this, triggering an error,
and with debug options enabled to find double free
and use after free? Which configurations?

Because if you did, you would find for example this
in drivers/virtio/virtio_vdpa.c:

        ret = register_virtio_device(&vd_dev->vdev);
        reg_dev = vd_dev;
        if (ret)
                goto err;

        vdpa_set_drvdata(vdpa, vd_dev);

        return 0;
        
err:    
        if (reg_dev)
                put_device(&vd_dev->vdev.dev);
        else
                kfree(vd_dev);
        return ret;




> ---
> Changes in v2:
> - modified the bug description to make it more clear;
> - changed the Fixes tag.
> ---
>  drivers/virtio/virtio.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
> index b9095751e43b..ac721b5597e8 100644
> --- a/drivers/virtio/virtio.c
> +++ b/drivers/virtio/virtio.c
> @@ -503,6 +503,7 @@ int register_virtio_device(struct virtio_device *dev)
>  
>  out_of_node_put:
>  	of_node_put(dev->dev.of_node);
> +	put_device(&dev->dev);
>  out_ida_remove:
>  	ida_free(&virtio_index_ida, dev->index);
>  out:
> -- 
> 2.25.1
>