linux-kernel - Re: [PATCH v2] mmc: dw_mmc: Fix to avoid potential NULL pointer dereference

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Date:   Tue, 19 Mar 2019 11:09:48 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Aditya Pakki <pakki001@....edu>
Cc:     Ulf Hansson <ulf.hansson@...aro.org>,
        linux-samsung-soc@...r.kernel.org,
        Heiko Stuebner <heiko@...ech.de>, linux-mmc@...r.kernel.org,
        kjlu@....edu, linux-kernel@...r.kernel.org,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Jaehoon Chung <jh80.chung@...sung.com>,
        linux-rockchip@...ts.infradead.org, Kukjin Kim <kgene@...nel.org>,
        Jun Nie <jun.nie@...aro.org>, Shawn Guo <shawnguo@...nel.org>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2] mmc: dw_mmc: Fix to avoid potential NULL pointer
 dereference

On 19/03/2019 01:45, Aditya Pakki wrote:
> of_match_node can fail and return NULL in case no matching structure.
> The patches checks for such a scenario and returns -ENXIO.

FWIW, it looks like most of these instances could be cleaned up even 
more with of_device_get_match_data().

In general, do bear in mind that adding these NULL checks *everywhere* 
will in many cases just amount to useless dead code - a pure DT-based 
driver can usually freely assume of_match_node() returns non-NULL for 
its own device and match table in its probe routine, because that probe 
routine only ever gets called if of_driver_match_device() has already 
made the same match in the first place.

Robin.

> ---
> V1: Added files dw_mmc-zx.c and dw_mmc-rockchip.c
> 
> Signed-off-by: Aditya Pakki <pakki001@....edu>
> ---
>   drivers/mmc/host/dw_mmc-exynos.c   | 2 ++
>   drivers/mmc/host/dw_mmc-k3.c       | 2 ++
>   drivers/mmc/host/dw_mmc-pltfm.c    | 2 ++
>   drivers/mmc/host/dw_mmc-rockchip.c | 2 ++
>   drivers/mmc/host/dw_mmc-zx.c       | 2 ++
>   5 files changed, 10 insertions(+)
> 
> diff --git a/drivers/mmc/host/dw_mmc-exynos.c b/drivers/mmc/host/dw_mmc-exynos.c
> index d46c3439b508..8a75d7314606 100644
> --- a/drivers/mmc/host/dw_mmc-exynos.c
> +++ b/drivers/mmc/host/dw_mmc-exynos.c
> @@ -554,6 +554,8 @@ static int dw_mci_exynos_probe(struct platform_device *pdev)
>   	int ret;
>   
>   	match = of_match_node(dw_mci_exynos_match, pdev->dev.of_node);
> +	if (!match)
> +		return -ENXIO;
>   	drv_data = match->data;
>   
>   	pm_runtime_get_noresume(&pdev->dev);
> diff --git a/drivers/mmc/host/dw_mmc-k3.c b/drivers/mmc/host/dw_mmc-k3.c
> index 89cdb3d533bb..cc50b7546a20 100644
> --- a/drivers/mmc/host/dw_mmc-k3.c
> +++ b/drivers/mmc/host/dw_mmc-k3.c
> @@ -459,6 +459,8 @@ static int dw_mci_k3_probe(struct platform_device *pdev)
>   	const struct of_device_id *match;
>   
>   	match = of_match_node(dw_mci_k3_match, pdev->dev.of_node);
> +	if (!match)
> +		return -ENXIO;
>   	drv_data = match->data;
>   
>   	return dw_mci_pltfm_register(pdev, drv_data);
> diff --git a/drivers/mmc/host/dw_mmc-pltfm.c b/drivers/mmc/host/dw_mmc-pltfm.c
> index 58c13e21bd5a..b1948989f617 100644
> --- a/drivers/mmc/host/dw_mmc-pltfm.c
> +++ b/drivers/mmc/host/dw_mmc-pltfm.c
> @@ -82,6 +82,8 @@ static int dw_mci_pltfm_probe(struct platform_device *pdev)
>   
>   	if (pdev->dev.of_node) {
>   		match = of_match_node(dw_mci_pltfm_match, pdev->dev.of_node);
> +		if (!match)
> +			return -ENXIO;
>   		drv_data = match->data;
>   	}
>   
> diff --git a/drivers/mmc/host/dw_mmc-rockchip.c b/drivers/mmc/host/dw_mmc-rockchip.c
> index 8c86a800a8fd..20e3471260ea 100644
> --- a/drivers/mmc/host/dw_mmc-rockchip.c
> +++ b/drivers/mmc/host/dw_mmc-rockchip.c
> @@ -344,6 +344,8 @@ static int dw_mci_rockchip_probe(struct platform_device *pdev)
>   		return -ENODEV;
>   
>   	match = of_match_node(dw_mci_rockchip_match, pdev->dev.of_node);
> +	if (!match)
> +		return -ENXIO;
>   	drv_data = match->data;
>   
>   	pm_runtime_get_noresume(&pdev->dev);
> diff --git a/drivers/mmc/host/dw_mmc-zx.c b/drivers/mmc/host/dw_mmc-zx.c
> index c06b5393312f..abea35431045 100644
> --- a/drivers/mmc/host/dw_mmc-zx.c
> +++ b/drivers/mmc/host/dw_mmc-zx.c
> @@ -213,6 +213,8 @@ static int dw_mci_zx_probe(struct platform_device *pdev)
>   	const struct of_device_id *match;
>   
>   	match = of_match_node(dw_mci_zx_match, pdev->dev.of_node);
> +	if (!match)
> +		return -ENXIO;
>   	drv_data = match->data;
>   
>   	return dw_mci_pltfm_register(pdev, drv_data);
>