Re: [lm-sensors] [PATCH v3] hwmon: (lm92) Prevent overflow problem when writing large limits

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

On Tue, Aug 05, 2014 at 10:08:31AM +0800, Axel Lin wrote:
> On platforms with sizeof(int) < sizeof(long), writing a temperature
> limit larger than MAXINT will result in unpredictable limit values
> written to the chip. Avoid auto-conversion from long to int to fix
> the problem.
> 
> The hysteresis temperature range depends on the value of
> data->temp[attr->index], since val is subtracted from it.
> Use a wider clamp, [-120000, 220000] should do to cover the
> possible range.
> 
> Also uses clamp_val to simplify the code a bit.
> 
> Signed-off-by: Axel Lin <axel.lin@ingics.com>
> ---
>  drivers/hwmon/lm92.c | 11 +++++------
>  1 file changed, 5 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/hwmon/lm92.c b/drivers/hwmon/lm92.c
> index d2060e2..08a261d 100644
> --- a/drivers/hwmon/lm92.c
> +++ b/drivers/hwmon/lm92.c
> @@ -74,12 +74,9 @@ static inline int TEMP_FROM_REG(s16 reg)
>  	return reg / 8 * 625 / 10;
>  }
>  
> -static inline s16 TEMP_TO_REG(int val)
> +static inline s16 TEMP_TO_REG(long val)
>  {
> -	if (val <= -60000)
> -		return -60000 * 10 / 625 * 8;
> -	if (val >= 160000)
> -		return 160000 * 10 / 625 * 8;
> +	val = clamp_val(val, -60000, 160000);
>  	return val * 10 / 625 * 8;
>  }
>  
> @@ -206,8 +203,10 @@ static ssize_t set_temp_hyst(struct device *dev,
>  	if (err)
>  		return err;
>  
> +	val = clamp_val(val, -120000, 220000);
>  	mutex_lock(&data->update_lock);
> -	data->temp[t_hyst] = TEMP_FROM_REG(data->temp[attr->index]) - val;
> +	 data->temp[t_hyst] > +		TEMP_TO_REG(TEMP_FROM_REG(data->temp[attr->index]) - val);
>  	i2c_smbus_write_word_swapped(client, LM92_REG_TEMP_HYST,
>  				     TEMP_TO_REG(data->temp[t_hyst]));

Hi Axel,

Almost ... unfortunately, now you've got TEMP_TO_REG() on data->temp[t_hyst]
twice. No need to resend, I fixed it up myself.

Thanks,
Guenter

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