Re: [PATCH v2] dma-mapping: Use dma_get_mask in dma_addressing_limited

[Michael S. Tsirkin]

On Mon, Jul 22, 2019 at 06:51:49PM +0200, Eric Auger wrote:
> We currently have cases where the dma_addressing_limited() gets
> called with dma_mask unset. This causes a NULL pointer dereference.
> 
> Use dma_get_mask() accessor to prevent the crash.
> 
> Fixes: b866455423e0 ("dma-mapping: add a dma_addressing_limited helper")
> Signed-off-by: Eric Auger <eric.auger@xxxxxxxxxx>

Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx>

If possible I really prefer this approach: avoids changing all callers
and uses documented interfaces.

> ---
> 
> v1 -> v2:
> - was [PATCH 1/2] dma-mapping: Protect dma_addressing_limited
>   against NULL dma_mask
> - Use dma_get_mask
> ---
>  include/linux/dma-mapping.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
> index e11b115dd0e4..f7d1eea32c78 100644
> --- a/include/linux/dma-mapping.h
> +++ b/include/linux/dma-mapping.h
> @@ -689,8 +689,8 @@ static inline int dma_coerce_mask_and_coherent(struct device *dev, u64 mask)
>   */
>  static inline bool dma_addressing_limited(struct device *dev)
>  {
> -	return min_not_zero(*dev->dma_mask, dev->bus_dma_mask) <
> -		dma_get_required_mask(dev);
> +	return min_not_zero(dma_get_mask(dev), dev->bus_dma_mask) <
> +			    dma_get_required_mask(dev);
>  }
>  
>  #ifdef CONFIG_ARCH_HAS_SETUP_DMA_OPS
> -- 
> 2.20.1