[PATCH v11 21/40] virtio_ring: packed: introduce virtqueue_resize_packed()

[Jason Wang]

在 2022/6/29 14:56, Xuan Zhuo 写道:
> virtio ring packed supports resize.
>
> Only after the new vring is successfully allocated based on the new num,
> we will release the old vring. In any case, an error is returned,
> indicating that the vring still points to the old vring.
>
> In the case of an error, re-initialize(by virtqueue_reinit_packed()) the
> virtqueue to ensure that the vring can be used.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo at linux.alibaba.com>
> ---
>   drivers/virtio/virtio_ring.c | 29 +++++++++++++++++++++++++++++
>   1 file changed, 29 insertions(+)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 650f701a5480..4860787286db 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -2042,6 +2042,35 @@ static struct virtqueue *vring_create_virtqueue_packed(
>   	return NULL;
>   }
>   
> +static int virtqueue_resize_packed(struct virtqueue *_vq, u32 num)
> +{
> +	struct vring_virtqueue_packed vring = {};
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +	struct virtio_device *vdev = _vq->vdev;
> +	int err;
> +
> +	if (vring_alloc_queue_packed(&vring, vdev, num))
> +		goto err_ring;
> +
> +	err = vring_alloc_state_extra_packed(&vring);
> +	if (err)
> +		goto err_state_extra;
> +
> +	vring_free(&vq->vq);
> +
> +	virtqueue_init(vq, vring.vring.num);
> +	virtqueue_vring_attach_packed(vq, &vring);
> +	virtqueue_vring_init_packed(vq);
> +
> +	return 0;
> +
> +err_state_extra:
> +	vring_free_packed(&vring, vdev);
> +err_ring:
> +	virtqueue_reinit_packed(vq);


So desc_state and desc_extra has been freed vring_free_packed() when 
vring_alloc_state_extra_packed() fails. We might get use-after-free here?

Actually, I think for resize we need

1) detach old
2) allocate new
3) if 2) succeed, attach new otherwise attach old

This seems more clearer than the current logic?

Thanks


> +	return -ENOMEM;
> +}
> +
>   
>   /*
>    * Generic functions and exported symbols.