linux-kernel - Re: [PATCH] mtd: nand: vf610_nfc: add NULL check on of_match

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Date:   Mon, 17 Jul 2017 22:46:19 +0200
From:   Boris Brezillon <boris.brezillon@...e-electrons.com>
To:     "Gustavo A. R. Silva" <garsilva@...eddedor.com>
Cc:     Stefan Agner <stefan@...er.ch>,
        Richard Weinberger <richard@....at>,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Marek Vasut <marek.vasut@...il.com>,
        Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mtd: nand: vf610_nfc: add NULL check on
 of_match_device() return value

Le Fri, 7 Jul 2017 01:59:26 -0500,
"Gustavo A. R. Silva" <garsilva@...eddedor.com> a écrit :

> 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/mtd/nand/vf610_nfc.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/mtd/nand/vf610_nfc.c b/drivers/mtd/nand/vf610_nfc.c
> index 744ab10..ca0ab96 100644
> --- a/drivers/mtd/nand/vf610_nfc.c
> +++ b/drivers/mtd/nand/vf610_nfc.c
> @@ -674,6 +674,11 @@ static int vf610_nfc_probe(struct platform_device *pdev)
>  	}
>  
>  	of_id = of_match_device(vf610_nfc_dt_ids, &pdev->dev);
> +	if (!of_id) {
> +		dev_err(&pdev->dev, "Failed to match device!\n");
> +		return -ENODEV;
> +	}
> +

While this check is functionally correct, this case cannot happen,
because this is DT-only driver, and without a valid match in
vf610_nfc_dt_ids the dev wouldn't have been probed in the first place.

I'll let Stefan decide whether he wants it or not, but I see no real
reason for this extra check. 

>  	nfc->variant = (enum vf610_nfc_variant)of_id->data;
>  
>  	for_each_available_child_of_node(nfc->dev->of_node, child) {