linux-kernel - Re: [PATCH v5 1/2] hwmon: (lm90) Prevent integer underflows of temperature calculations

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Date:   Thu, 24 Jun 2021 07:14:48 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Zhang Rui <rui.zhang@...el.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Amit Kucheria <amitk@...nel.org>,
        Jean Delvare <jdelvare@...e.com>, linux-hwmon@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-tegra@...r.kernel.org
Subject: Re: [PATCH v5 1/2] hwmon: (lm90) Prevent integer underflows of
 temperature calculations

On Wed, Jun 23, 2021 at 07:22:30AM +0300, Dmitry Osipenko wrote:
> The min/max/crit and all other temperature values that are passed to
> the driver are unlimited and value that is close to INT_MIN results in
> integer underflow of the temperature calculations made by the driver
> for LM99 sensor. Temperature hysteresis is among those values that need
> to be limited, but limiting of hysteresis is independent from the sensor
> version. Add the missing limits.
> 
> Signed-off-by: Dmitry Osipenko <digetx@...il.com>

Applied.

Thanks,
Guenter

> ---
>  drivers/hwmon/lm90.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/hwmon/lm90.c b/drivers/hwmon/lm90.c
> index b53f17511b05..567b7c521f38 100644
> --- a/drivers/hwmon/lm90.c
> +++ b/drivers/hwmon/lm90.c
> @@ -1029,8 +1029,11 @@ static int lm90_set_temp11(struct lm90_data *data, int index, long val)
>  	int err;
>  
>  	/* +16 degrees offset for temp2 for the LM99 */
> -	if (data->kind == lm99 && index <= 2)
> +	if (data->kind == lm99 && index <= 2) {
> +		/* prevent integer underflow */
> +		val = max(val, -128000l);
>  		val -= 16000;
> +	}
>  
>  	if (data->kind == adt7461 || data->kind == tmp451)
>  		data->temp11[index] = temp_to_u16_adt7461(data, val);
> @@ -1089,8 +1092,11 @@ static int lm90_set_temp8(struct lm90_data *data, int index, long val)
>  	int err;
>  
>  	/* +16 degrees offset for temp2 for the LM99 */
> -	if (data->kind == lm99 && index == 3)
> +	if (data->kind == lm99 && index == 3) {
> +		/* prevent integer underflow */
> +		val = max(val, -128000l);
>  		val -= 16000;
> +	}
>  
>  	if (data->kind == adt7461 || data->kind == tmp451)
>  		data->temp8[index] = temp_to_u8_adt7461(data, val);
> @@ -1137,6 +1143,9 @@ static int lm90_set_temphyst(struct lm90_data *data, long val)
>  	else
>  		temp = temp_from_s8(data->temp8[LOCAL_CRIT]);
>  
> +	/* prevent integer underflow */
> +	val = max(val, -128000l);
> +
>  	data->temp_hyst = hyst_to_reg(temp - val);
>  	err = i2c_smbus_write_byte_data(client, LM90_REG_W_TCRIT_HYST,
>  					data->temp_hyst);