linux-kernel - Re: [PATCH 1/3] mmc: sdhci-s3c: fix possible NULL pointer dereference when probed via platform

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Date:   Wed, 14 Apr 2021 17:25:25 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
To:     Ben Dooks <ben-linux@...ff.org>,
        Jaehoon Chung <jh80.chung@...sung.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>,
        Sylwester Nawrocki <snawrocki@...nel.org>
Subject: Re: [PATCH 1/3] mmc: sdhci-s3c: fix possible NULL pointer dereference
 when probed via platform

On 14/04/2021 17:12, Krzysztof Kozlowski wrote:
> The driver can be matched by legacy platform way or OF-device matching.
> In the first case, of_match_node() can return NULL, which immediately
> would be dereferenced to get the match data.
> 
> Addresses-Coverity: Dereference null return value
> Fixes: cd1b00eb24b0 ("mmc: sdhci-s3c: Add device tree support")
> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
> ---
> 
> Not tested on HW, but the code should be equivalent (plus safer).
> 
>  drivers/mmc/host/sdhci-s3c.c | 12 +++---------
>  1 file changed, 3 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/mmc/host/sdhci-s3c.c b/drivers/mmc/host/sdhci-s3c.c
> index f48a788a9d3d..8e1dca625620 100644
> --- a/drivers/mmc/host/sdhci-s3c.c
> +++ b/drivers/mmc/host/sdhci-s3c.c
> @@ -20,6 +20,7 @@
>  #include <linux/gpio.h>
>  #include <linux/module.h>
>  #include <linux/of.h>
> +#include <linux/of_device.h>
>  #include <linux/of_gpio.h>
>  #include <linux/pm.h>
>  #include <linux/pm_runtime.h>
> @@ -461,19 +462,12 @@ static int sdhci_s3c_parse_dt(struct device *dev,
>  }
>  #endif
>  
> -#ifdef CONFIG_OF
> -static const struct of_device_id sdhci_s3c_dt_match[];
> -#endif
> -
>  static inline struct sdhci_s3c_drv_data *sdhci_s3c_get_driver_data(
>  			struct platform_device *pdev)
>  {
>  #ifdef CONFIG_OF
> -	if (pdev->dev.of_node) {
> -		const struct of_device_id *match;
> -		match = of_match_node(sdhci_s3c_dt_match, pdev->dev.of_node);

Now I have second thoughts whether NULL pointer can actually happen.  If
device is matched via platform/board files, maybe the pdev->dev.of_node
will be NULL thus skipping this branch?

Could there be a case where device is matched via platform_device_id()
(which has different name than compatible!) and (pdev->dev.of_node) is
still assigned? Maybe in case of out of tree DTS?

Anyway, the patch makes the code simpler/smaller, so I still think it is
reasonable. Just the severity of issue is questionable...

Best regards,
Krzysztof