linux-kernel - Re: [PATCH] net: ethernet: mediatek: add NULL check on of_match

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Date:   Fri, 7 Jul 2017 16:57:17 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     "Gustavo A. R. Silva" <garsilva@...eddedor.com>
Cc:     Felix Fietkau <nbd@...nwrt.org>, John Crispin <blogic@...nwrt.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        netdev@...r.kernel.org, linux-mediatek@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] net: ethernet: mediatek: add NULL check on
 of_match_device() return value

On Fri, Jul 07, 2017 at 02:11:35AM -0500, Gustavo A. R. Silva wrote:
> Check return value from call to of_match_device()
> in order to prevent a NULL pointer dereference.
> 
> In case of NULL print error message and return -ENODEV
> 
> Signed-off-by: Gustavo A. R. Silva <garsilva@...eddedor.com>
> ---
>  drivers/net/ethernet/mediatek/mtk_eth_soc.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> index adaaafc..6a77dea 100644
> --- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> +++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> @@ -2408,6 +2408,11 @@ static int mtk_probe(struct platform_device *pdev)
>  	int i;
>  
>  	match = of_match_device(of_mtk_match, &pdev->dev);
> +	if (!match) {
> +		dev_err(&pdev->dev, "failed to match device\n");
> +		return -ENODEV;
> +	}
> +
>  	soc = (struct mtk_soc_data *)match->data;

Hi Gustavo

I think you are fixing the wrong thing. The soc variable is unused. Also,

const struct of_device_id of_mtk_match[] = {
        { .compatible = "mediatek,mt2701-eth" },
        {},
};

So match->data is NULL. This code is all pointless and should be
removed, rather than try to avoid a NULL pointer dereference which can
not actually happen.

	Andrew