linux-kernel - Re: [PATCH v2] iio: vadc: Fix potential dereference of NULL pointer

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Message-ID: <20220520181323.00002892@huawei.com>
Date:   Fri, 20 May 2022 18:13:23 +0100
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     Yongzhi Liu <lyz_cs@....edu.cn>
CC:     <agross@...nel.org>, <bjorn.andersson@...aro.org>,
        <jic23@...nel.org>, <lars@...afoo.de>,
        <linux-arm-msm@...r.kernel.org>, <linux-iio@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <fuyq@....pku.edu.cn>
Subject: Re: [PATCH v2] iio: vadc: Fix potential dereference of NULL pointer

On Wed, 18 May 2022 22:50:55 -0700
Yongzhi Liu <lyz_cs@....edu.cn> wrote:

> The return value of vadc_get_channel() needs to be checked
> to avoid use of NULL pointer. Fix this by adding the null
> pointer check on prop.
> 
> Fixes: 0917de94c ("iio: vadc: Qualcomm SPMI PMIC voltage ADC driver")
> 
> Signed-off-by: Yongzhi Liu <lyz_cs@....edu.cn>
This function has a lot of goto err; where err just results in
a print.

My suggestion is to just drop that print and use
error specific prints as you have done here, then use direct returns.

> ---
>  drivers/iio/adc/qcom-spmi-vadc.c | 23 ++++++++++++++++++++++-
>  1 file changed, 22 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iio/adc/qcom-spmi-vadc.c b/drivers/iio/adc/qcom-spmi-vadc.c
> index 34202ba..9fa61fb 100644
> --- a/drivers/iio/adc/qcom-spmi-vadc.c
> +++ b/drivers/iio/adc/qcom-spmi-vadc.c
> @@ -358,14 +358,25 @@ static int vadc_measure_ref_points(struct vadc_priv *vadc)
>  	vadc->graph[VADC_CALIB_ABSOLUTE].dx = VADC_ABSOLUTE_RANGE_UV;
>  
>  	prop = vadc_get_channel(vadc, VADC_REF_1250MV);
> +	if (!prop) {
> +		dev_err(vadc->dev, "Please define 1.25V channel\n");
> +		ret = -ENODEV;
> +		goto err;
> +	}
>  	ret = vadc_do_conversion(vadc, prop, &read_1);
>  	if (ret)
>  		goto err;
>  
>  	/* Try with buffered 625mV channel first */
>  	prop = vadc_get_channel(vadc, VADC_SPARE1);
> -	if (!prop)
> +	if (!prop) {
>  		prop = vadc_get_channel(vadc, VADC_REF_625MV);
> +		if (!prop) {
> +			dev_err(vadc->dev, "Please define 0.625V channel\n");
> +			ret = -ENODEV;
> +			goto err;
> +		}
> +	}
>  
>  	ret = vadc_do_conversion(vadc, prop, &read_2);
>  	if (ret)
> @@ -381,11 +392,21 @@ static int vadc_measure_ref_points(struct vadc_priv *vadc)
>  
>  	/* Ratiometric calibration */
>  	prop = vadc_get_channel(vadc, VADC_VDD_VADC);
> +	if (!prop) {
> +		dev_err(vadc->dev, "Please define VDD channel\n");
> +		ret = -ENODEV;
> +		goto err;
> +	}
>  	ret = vadc_do_conversion(vadc, prop, &read_1);
>  	if (ret)
>  		goto err;
>  
>  	prop = vadc_get_channel(vadc, VADC_GND_REF);
> +	if (!prop) {
> +		dev_err(vadc->dev, "Please define GND channel\n");
> +		ret = -ENODEV;
> +		goto err;
> +	}
>  	ret = vadc_do_conversion(vadc, prop, &read_2);
>  	if (ret)
>  		goto err;