linux-kernel - Re: [PATCH v4 1/2] hwmon: (lm90) Prevent integer underflows of temperature calculations

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Date:   Tue, 22 Jun 2021 16:15:25 -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 v4 1/2] hwmon: (lm90) Prevent integer underflows of
 temperature calculations

On Tue, Jun 22, 2021 at 12:31:52AM +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>
> ---
>  drivers/hwmon/lm90.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/hwmon/lm90.c b/drivers/hwmon/lm90.c
> index b53f17511b05..ee6b8190f08e 100644
> --- a/drivers/hwmon/lm90.c
> +++ b/drivers/hwmon/lm90.c
> @@ -1028,6 +1028,9 @@ static int lm90_set_temp11(struct lm90_data *data, int index, long val)
>  	struct reg *regp = &reg[index];
>  	int err;
>  
> +	/* prevent integer underflow */
> +	val = max(val, -128000l);
> +

This and the adjustment below can be moved into the if() statement for lm99.
There is no need to affect other chips.

>  	/* +16 degrees offset for temp2 for the LM99 */
>  	if (data->kind == lm99 && index <= 2)
>  		val -= 16000;
> @@ -1088,6 +1091,9 @@ static int lm90_set_temp8(struct lm90_data *data, int index, long val)
>  	struct i2c_client *client = data->client;
>  	int err;
>  
> +	/* prevent integer underflow */
> +	val = max(val, -128000l);
> +
>  	/* +16 degrees offset for temp2 for the LM99 */
>  	if (data->kind == lm99 && index == 3)
>  		val -= 16000;
> @@ -1130,6 +1136,9 @@ static int lm90_set_temphyst(struct lm90_data *data, long val)
>  	int temp;
>  	int err;
>  
> +	/* prevent integer underflow */
> +	val = max(val, -128000l);
> +
Please move this further below, just before val is used, to better
show the context why it is needed.

Thanks,
Guenter

>  	if (data->kind == adt7461 || data->kind == tmp451)
>  		temp = temp_from_u8_adt7461(data, data->temp8[LOCAL_CRIT]);
>  	else if (data->kind == max6646)
> -- 
> 2.30.2
>