linux-kernel - Re: [PATCH v3] iio: vadc: Fix potential dereference of NULL pointer

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Message-ID: <20220522120109.7ead18a7@jic23-huawei>
Date:   Sun, 22 May 2022 12:01:09 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Yongzhi Liu <lyz_cs@....edu.cn>
Cc:     agross@...nel.org, bjorn.andersson@...aro.org, lars@...afoo.de,
        svarbanov@...sol.com, iivanov@...sol.com,
        jonathan.cameron@...wei.com, linux-arm-msm@...r.kernel.org,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
        fuyq@....pku.edu.cn
Subject: Re: [PATCH v3] iio: vadc: Fix potential dereference of NULL pointer

On Fri, 20 May 2022 20:35:35 -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 and dropping general error prints.
> 
> Fixes: 0917de94c02f ("iio: vadc: Qualcomm SPMI PMIC voltage ADC driver")
> Signed-off-by: Yongzhi Liu <lyz_cs@....edu.cn>
Hi, 

Heading in the right direction. A few comments inline.

Thanks,

Jonathan

> ---
>  drivers/iio/adc/qcom-spmi-vadc.c | 38 ++++++++++++++++++++++++++++----------
>  1 file changed, 28 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/iio/adc/qcom-spmi-vadc.c b/drivers/iio/adc/qcom-spmi-vadc.c
> index 34202ba..43a52b1 100644
> --- a/drivers/iio/adc/qcom-spmi-vadc.c
> +++ b/drivers/iio/adc/qcom-spmi-vadc.c
> @@ -358,22 +358,33 @@ 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;
> +		return ret;

		return -ENODEV;

Same for the other case below.

> +	}
>  	ret = vadc_do_conversion(vadc, prop, &read_1);
>  	if (ret)
> -		goto err;

Good to add a note to the patch description that
vadc_do_conversion() already provides error prints in at least
some of it's error paths.  Thus it is reasonable to drop the
extra reporting in this function.

> +		return ret;
>  
>  	/* 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;
> +			return ret;
> +		}
> +	}
>  
>  	ret = vadc_do_conversion(vadc, prop, &read_2);
>  	if (ret)
> -		goto err;
> +		return ret;
>  
>  	if (read_1 == read_2) {
>  		ret = -EINVAL;
> -		goto err;
> +		return ret;
>  	}
>  
>  	vadc->graph[VADC_CALIB_ABSOLUTE].dy = read_1 - read_2;
> @@ -381,25 +392,32 @@ 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;
> +		return ret;
> +	}
>  	ret = vadc_do_conversion(vadc, prop, &read_1);
>  	if (ret)
> -		goto err;
> +		return ret;
>  
>  	prop = vadc_get_channel(vadc, VADC_GND_REF);
> +	if (!prop) {
> +		dev_err(vadc->dev, "Please define GND channel\n");
> +		ret = -ENODEV;
> +		return ret;
> +	}
>  	ret = vadc_do_conversion(vadc, prop, &read_2);
>  	if (ret)
> -		goto err;
> +		return ret;
>  
>  	if (read_1 == read_2) {
>  		ret = -EINVAL;
> -		goto err;
> +		return ret;
>  	}
>  
>  	vadc->graph[VADC_CALIB_RATIOMETRIC].dy = read_1 - read_2;
>  	vadc->graph[VADC_CALIB_RATIOMETRIC].gnd = read_2;
> -err:
> -	if (ret)
> -		dev_err(vadc->dev, "measure reference points failed\n");
>  
>  	return ret;
>  }