linux-kernel - Re: [PATCH] thermal: tegra: dereference the pointer after null check

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Message-ID: <20170901190835.GA14011@ulmo>
Date:   Fri, 1 Sep 2017 21:08:35 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Nicolin Chen <nicoleotsuka@...il.com>
Cc:     rui.zhang@...el.com, edubezval@...il.com, jonathanh@...dia.com,
        wni@...dia.com, linux-pm@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org,
        srikars@...dia.com
Subject: Re: [PATCH] thermal: tegra: dereference the pointer after null check

On Thu, Aug 31, 2017 at 04:52:29PM -0700, Nicolin Chen wrote:
> The dev pointer is going through a null check after a dereference.
> So this patch just reverses that.
> 
> Signed-off-by: Nicolin Chen <nicoleotsuka@...il.com>
> ---
>  drivers/thermal/tegra/soctherm.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/thermal/tegra/soctherm.c b/drivers/thermal/tegra/soctherm.c
> index 7d2db23..6718799 100644
> --- a/drivers/thermal/tegra/soctherm.c
> +++ b/drivers/thermal/tegra/soctherm.c
> @@ -478,7 +478,7 @@ static int throttrip_program(struct device *dev,
>  			     struct soctherm_throt_cfg *stc,
>  			     int trip_temp)
>  {
> -	struct tegra_soctherm *ts = dev_get_drvdata(dev);
> +	struct tegra_soctherm *ts;
>  	int temp, cpu_throt, gpu_throt;
>  	unsigned int throt;
>  	u32 r, reg_off;
> @@ -486,6 +486,8 @@ static int throttrip_program(struct device *dev,
>  	if (!dev || !sg || !stc || !stc->init)
>  		return -EINVAL;
>  
> +	ts = dev_get_drvdata(dev);
> +
>  	temp = enforce_temp_range(dev, trip_temp) / ts->soc->thresh_grain;
>  
>  	/* Hardcode LIGHT on LEVEL1 and HEAVY on LEVEL2 */

I don't see a case where dev is ever going to be NULL here. Therefore, I
think a better patch would be to just drop the !dev test and leave the
rest of the code as-is.

Thierry

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