linux-kernel - Re: [PATCH] dmaengine: rcar-dmac: avoid array overflow

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Date:   Fri, 28 Jul 2017 18:08:09 +0200
From:   "Niklas Söderlund" <niklas.soderlund@...natech.se>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Vinod Koul <vinod.koul@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>,
        dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dmaengine: rcar-dmac: avoid array overflow

Hi Arnd,

On 2017-07-28 15:15:49 +0200, Arnd Bergmann wrote:
> Building with CONFIG_UBSAN_SANITIZE_ALL shows this warning:
> 
> drivers/dma/sh/rcar-dmac.c: In function 'rcar_dmac_chan_prep_sg':
> drivers/dma/sh/rcar-dmac.c:839:29: error: array subscript is above array bounds [-Werror=array-bounds]
>   desc->chcr = chcr | chcr_ts[desc->xfer_shift];
> 
> As the compiler doesn't know what the xfer_size is, it is impossible
> to rule out the array overflow here. As we know that xfer_size
> can only be within enum dma_slave_buswidth, this will not overflow
> for correct users, and adding a range check will handle the
> obscure case and shut up the warning.
> 
> Fixes: 87244fe5abdf ("dmaengine: rcar-dmac: Add Renesas R-Car Gen2 DMA Controller (DMAC) driver")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@...natech.se>

> ---
>  drivers/dma/sh/rcar-dmac.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/dma/sh/rcar-dmac.c b/drivers/dma/sh/rcar-dmac.c
> index ffcadca53243..f5b28eb4009e 100644
> --- a/drivers/dma/sh/rcar-dmac.c
> +++ b/drivers/dma/sh/rcar-dmac.c
> @@ -836,7 +836,8 @@ static void rcar_dmac_chan_configure_desc(struct rcar_dmac_chan *chan,
>  	}
>  
>  	desc->xfer_shift = ilog2(xfer_size);
> -	desc->chcr = chcr | chcr_ts[desc->xfer_shift];
> +	if (desc->xfer_shift < ARRAY_SIZE(chcr_ts))
> +		desc->chcr = chcr | chcr_ts[desc->xfer_shift];
>  }
>  
>  /*
> -- 
> 2.9.0
> 

-- 
Regards,
Niklas Söderlund