Re: [PATCH 1/4] dmaengine: zynqmp_dma: Typecast the variable to handle overflow

[Michael Tretter]

Hi Harini,

On Tue, 14 Sep 2021 13:58:14 +0530, Harini Katakam wrote:
> From: Shravya Kumbham <shravya.kumbham@xxxxxxxxxx>
> 
> In zynqmp_dma_alloc/free_chan_resources functions there is a
> potential overflow in the below expressions.
> 
> dma_alloc_coherent(chan->dev, (2 * chan->desc_size *
> 		   ZYNQMP_DMA_NUM_DESCS),
> 		   &chan->desc_pool_p, GFP_KERNEL);
> 
> dma_free_coherent(chan->dev,(2 * ZYNQMP_DMA_DESC_SIZE(chan) *
>                  ZYNQMP_DMA_NUM_DESCS),
>                 chan->desc_pool_v, chan->desc_pool_p);
> 
> The arguments desc_size and ZYNQMP_DMA_NUM_DESCS are 32 bit. Though
> this overflow condition is not observed but it is a potential problem
> in the case of 32-bit multiplication. Hence fix it by using typecast.
> 
> Addresses-Coverity: Event overflow_before_widen.
> Signed-off-by: Shravya Kumbham <shravya.kumbham@xxxxxxxxxx>
> Reviewed-by: Radhey Shyam Pandey <radhey.shyam.pandey@xxxxxxxxxx>

Thanks for the patch.

Your SoB is missing in this and the other patches of this series.

> ---
>  drivers/dma/xilinx/zynqmp_dma.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/dma/xilinx/zynqmp_dma.c b/drivers/dma/xilinx/zynqmp_dma.c
> index 5fecf5aa6e85..2d0eba25739d 100644
> --- a/drivers/dma/xilinx/zynqmp_dma.c
> +++ b/drivers/dma/xilinx/zynqmp_dma.c
> @@ -490,7 +490,8 @@ static int zynqmp_dma_alloc_chan_resources(struct dma_chan *dchan)
>  	}
>  
>  	chan->desc_pool_v = dma_alloc_coherent(chan->dev,
> -					       (2 * chan->desc_size * ZYNQMP_DMA_NUM_DESCS),
> +					       ((size_t)(2 * chan->desc_size) *
> +						ZYNQMP_DMA_NUM_DESCS),

Wouldn't it be easier to change the type of chan->desc_size to size_t? Maybe
we could also just calculate the size of the descriptor pool during probe() to
make the code more readable?

I also noticed that there is the ZYNQMP_DMA_DESC_SIZE() macro, which is
inconsistently used in the driver. Maybe you could cleanup this as well as you
are at it?

>  					       &chan->desc_pool_p, GFP_KERNEL);
>  	if (!chan->desc_pool_v)
>  		return -ENOMEM;
> @@ -677,7 +678,8 @@ static void zynqmp_dma_free_chan_resources(struct dma_chan *dchan)
>  	zynqmp_dma_free_descriptors(chan);
>  	spin_unlock_irqrestore(&chan->lock, irqflags);
>  	dma_free_coherent(chan->dev,
> -		(2 * ZYNQMP_DMA_DESC_SIZE(chan) * ZYNQMP_DMA_NUM_DESCS),
> +		((size_t)(2 * ZYNQMP_DMA_DESC_SIZE(chan)) *
> +		 ZYNQMP_DMA_NUM_DESCS),

With a pre-calculated descriptor pool size, recalculating the size here
wouldn't be necessary anymore.

Michael

>  		chan->desc_pool_v, chan->desc_pool_p);
>  	kfree(chan->sw_desc_pool);
>  	pm_runtime_mark_last_busy(chan->dev);
> -- 
> 2.17.1
> 
> 
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