Re: [PATCH v2 1/2] hwmon: (lm90) Prevent integer overflow of temperature calculations

[Guenter Roeck <linux@roeck-us.net>]

On Mon, Jun 21, 2021 at 12:14:07AM +0300, Dmitry Osipenko wrote:
> The minimum temperature value that is passed to the driver is unlimited
> and value that is close to INT_MIN results in integer overflow of
> temperature calculations made by the driver. Limit the value in order
> to prevent the overflow. For now the overflow condition is harmless,
> but thermal framework won't work properly once we will support the
> set_trips() callback because it will pass INT_MIN value to the driver.
> 

AFAICS that should only happen for lm99 because all other values
are bound in the temp_to_xxx functions. Where else do you see an
overflow (or underflow) ?

Thanks,
Guenter

> Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
> ---
>  drivers/hwmon/lm90.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/hwmon/lm90.c b/drivers/hwmon/lm90.c
> index b53f17511b05..6e2fa976098f 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 overflow */
> +	val = max(val, -128000l);
> +
>  	/* +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 overflow */
> +	val = max(val, -128000l);
> +
>  	/* +16 degrees offset for temp2 for the LM99 */
>  	if (data->kind == lm99 && index == 3)
>  		val -= 16000;
> -- 
> 2.30.2
>