RE: [PATCH 1/3] udmabuf: Keep track current device mappings

[Kasireddy, Vivek]

Hi Andrew,

> When a device attaches to and maps our buffer we need to keep track
> of this mapping/device. This is needed for synchronization with these
> devices when beginning and ending CPU access for instance. Add a list
> that tracks device mappings as part of {map,unmap}_udmabuf().
> 
> Signed-off-by: Andrew Davis <afd@xxxxxx>
> ---
>  drivers/dma-buf/udmabuf.c | 43
> +++++++++++++++++++++++++++++++++++++--
>  1 file changed, 41 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
> index c406459996489..3a23f0a7d112a 100644
> --- a/drivers/dma-buf/udmabuf.c
> +++ b/drivers/dma-buf/udmabuf.c
> @@ -28,6 +28,14 @@ struct udmabuf {
>  	struct page **pages;
>  	struct sg_table *sg;
>  	struct miscdevice *device;
> +	struct list_head attachments;
> +	struct mutex lock;
> +};
> +
> +struct udmabuf_attachment {
> +	struct device *dev;
> +	struct sg_table *table;
> +	struct list_head list;
>  };
> 
>  static vm_fault_t udmabuf_vm_fault(struct vm_fault *vmf)
> @@ -120,14 +128,42 @@ static void put_sg_table(struct device *dev, struct
> sg_table *sg,
>  static struct sg_table *map_udmabuf(struct dma_buf_attachment *at,
>  				    enum dma_data_direction direction)
>  {
> -	return get_sg_table(at->dev, at->dmabuf, direction);
> +	struct udmabuf *ubuf = at->dmabuf->priv;
> +	struct udmabuf_attachment *a;
> +
> +	a = kzalloc(sizeof(*a), GFP_KERNEL);
> +	if (!a)
> +		return ERR_PTR(-ENOMEM);
> +
> +	a->table = get_sg_table(at->dev, at->dmabuf, direction);
> +	if (IS_ERR(a->table)) {
> +		kfree(a);
> +		return a->table;
Isn't that a use-after-free bug?
Rest of the patch lgtm.

Thanks,
Vivek

> +	}
> +
> +	a->dev = at->dev;
> +
> +	mutex_lock(&ubuf->lock);
> +	list_add(&a->list, &ubuf->attachments);
> +	mutex_unlock(&ubuf->lock);
> +
> +	return a->table;
>  }
> 
>  static void unmap_udmabuf(struct dma_buf_attachment *at,
>  			  struct sg_table *sg,
>  			  enum dma_data_direction direction)
>  {
> -	return put_sg_table(at->dev, sg, direction);
> +	struct udmabuf_attachment *a = at->priv;
> +	struct udmabuf *ubuf = at->dmabuf->priv;
> +
> +	mutex_lock(&ubuf->lock);
> +	list_del(&a->list);
> +	mutex_unlock(&ubuf->lock);
> +
> +	put_sg_table(at->dev, sg, direction);
> +
> +	kfree(a);
>  }
> 
>  static void release_udmabuf(struct dma_buf *buf)
> @@ -263,6 +299,9 @@ static long udmabuf_create(struct miscdevice
> *device,
>  		memfd = NULL;
>  	}
> 
> +	INIT_LIST_HEAD(&ubuf->attachments);
> +	mutex_init(&ubuf->lock);
> +
>  	exp_info.ops  = &udmabuf_ops;
>  	exp_info.size = ubuf->pagecount << PAGE_SHIFT;
>  	exp_info.priv = ubuf;
> --
> 2.39.2