linux-kernel - Re: [PATCH] thermal: bcm2835: Fix crash in bcm2835_thermal

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Date:   Tue, 29 Jan 2019 10:52:56 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Phil Elwell <phil@...pberrypi.org>, Eric Anholt <eric@...olt.net>,
        Stefan Wahren <stefan.wahren@...e.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        bcm-kernel-feedback-list@...adcom.com,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        linux-pm@...r.kernel.org, linux-rpi-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] thermal: bcm2835: Fix crash in bcm2835_thermal_debugfs

On 29/01/2019 10:10, Phil Elwell wrote:
> "cat /sys/kernel/debug/bcm2835_thermal/regset" causes a NULL pointer
> dereference in bcm2835_thermal_debugfs. The driver makes use of the
> implementation details of the thermal framework to retrieve a pointer
> to its private data from a struct thermal_zone_device, and gets it
> wrong - leading to the crash. Instead, store its private data as the
> drvdata and retrieve the thermal_zone_device pointer from it.
> 
> Fixes: bcb7dd9ef206 ("thermal: bcm2835: add thermal driver for bcm2835 SoC")
> 
> Signed-off-by: Phil Elwell <phil@...pberrypi.org>

Reviewed-by: Daniel Lezcano <daniel.lezcano@...aro.org>

One question: do you really want the thermal driver to be loaded as a
module ? Don't you want to have it operational as soon as possible
instead of waiting the OS to boot and load the kernel module?

If a module format is not needed, then the thermal_zone field won't be
needed anymore because the 'remove' ops can be removed and the need of
the tz field to unregister it disappears.

> ---
>  drivers/thermal/broadcom/bcm2835_thermal.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/thermal/broadcom/bcm2835_thermal.c b/drivers/thermal/broadcom/bcm2835_thermal.c
> index 720760c..ba39647 100644
> --- a/drivers/thermal/broadcom/bcm2835_thermal.c
> +++ b/drivers/thermal/broadcom/bcm2835_thermal.c
> @@ -119,8 +119,7 @@ static const struct debugfs_reg32 bcm2835_thermal_regs[] = {
>  
>  static void bcm2835_thermal_debugfs(struct platform_device *pdev)
>  {
> -	struct thermal_zone_device *tz = platform_get_drvdata(pdev);
> -	struct bcm2835_thermal_data *data = tz->devdata;
> +	struct bcm2835_thermal_data *data = platform_get_drvdata(pdev);
>  	struct debugfs_regset32 *regset;
>  
>  	data->debugfsdir = debugfs_create_dir("bcm2835_thermal", NULL);
> @@ -266,7 +265,7 @@ static int bcm2835_thermal_probe(struct platform_device *pdev)
>  
>  	data->tz = tz;
>  
> -	platform_set_drvdata(pdev, tz);
> +	platform_set_drvdata(pdev, data);
>  
>  	/*
>  	 * Thermal_zone doesn't enable hwmon as default,
> @@ -290,8 +289,8 @@ static int bcm2835_thermal_probe(struct platform_device *pdev)
>  
>  static int bcm2835_thermal_remove(struct platform_device *pdev)
>  {
> -	struct thermal_zone_device *tz = platform_get_drvdata(pdev);
> -	struct bcm2835_thermal_data *data = tz->devdata;
> +	struct bcm2835_thermal_data *data = platform_get_drvdata(pdev);
> +	struct thermal_zone_device *tz = data->tz;
>  
>  	debugfs_remove_recursive(data->debugfsdir);
>  	thermal_zone_of_sensor_unregister(&pdev->dev, tz);
> 


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