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

Jason Wang
2022-07-01T09:28:25Z

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@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.