Re: [PATCH] dmaengine: dw-axi-dmac: Do not dereference NULL structure

[Andy Shevchenko]

On Fri, Jan 27, 2023 at 02:36:27PM -0800, Kees Cook wrote:
> If "vdesc" is NULL, it cannot be used with vd_to_axi_desc(). Leave
> "bytes" unchanged at 0. Seen under GCC 13 with -Warray-bounds:
> 
> ../drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c: In function 'dma_chan_tx_status':
> ../drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c:329:46: warning: array subscript 0 is outside array bounds of 'struct
> virt_dma_desc[46116860184273879]' [-Warray-bounds=]
>   329 |                 bytes = vd_to_axi_desc(vdesc)->length;
>       |                                              ^~
> 
> Fixes: 8e55444da65c ("dmaengine: dw-axi-dmac: Support burst residue granularity")
> Cc: Eugeniy Paltsev <Eugeniy.Paltsev@xxxxxxxxxxxx>
> Cc: Vinod Koul <vkoul@xxxxxxxxxx>
> Cc: dmaengine@xxxxxxxxxxxxxxx
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> ---
>  drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c b/drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c
> index 08af483331fd..4169e1d7d5ca 100644
> --- a/drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c
> +++ b/drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c
> @@ -325,8 +325,6 @@ dma_chan_tx_status(struct dma_chan *dchan, dma_cookie_t cookie,
>  		len = vd_to_axi_desc(vdesc)->hw_desc[0].len;
>  		completed_length = completed_blocks * len;
>  		bytes = length - completed_length;
> -	} else {
> -		bytes = vd_to_axi_desc(vdesc)->length;
>  	}
>  
>  	spin_unlock_irqrestore(&chan->vc.lock, flags);

If you want to fix it properly, the code should be modified like

	status = dma_cookie_status(dchan, cookie, txstate);
	if (status == DMA_COMPLETE || !txstate) {
		if (txstate)
			goto out;
		return status;
	}

	...

out:
	dma_set_residue(txstate, bytes);

	return status;

to be in accordance with the Documentation.

**OR**

the Documentation should be fixed to tell that if status is DMA_COMPLETE,
residue is undefined and assumed to be 0.

Vinod?

-- 
With Best Regards,
Andy Shevchenko