Re: [PATCH] hwmon: (nct6775) Fix loop limit

Paul Menzel
2018-06-13T20:06:21Z

Dear Guenter,

Am 13.06.2018 um 17:10 schrieb Guenter Roeck:
> Commit cc66b3038254 ("hwmon: (nct6775) Rework temperature source and label
> handling") changed a loop limit from "data->temp_label_num - 1" to "32",
> as part of moving from a string array to a bit mask. This results in the
> following error, reported by UBSAN.
>
> UBSAN: Undefined behaviour in drivers/hwmon/nct6775.c:4179:27
> shift exponent 32 is too large for 32-bit type 'long unsigned int'
>
> Similar to the original loop, the limit has to be one less than the
> number of bits.
>
> Fixes: cc66b3038254 ("hwmon: (nct6775) Rework temperature source and label handling")
> Reported-by: Paul Menzel <pmenzel+linux-hwmon@molgen.mpg.de>
> Cc: Paul Menzel <pmenzel+linux-hwmon@molgen.mpg.de>
> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> ---
> drivers/hwmon/nct6775.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/hwmon/nct6775.c b/drivers/hwmon/nct6775.c
> index aebce560bfaf..b14eb73bc3c9 100644
> --- a/drivers/hwmon/nct6775.c
> +++ b/drivers/hwmon/nct6775.c
> @@ -4175,7 +4175,7 @@ static int nct6775_probe(struct platform_device *pdev)
> * The temperature is already monitored if the respective bit in <mask>
> * is set.
> */
> - for (i = 0; i < 32; i++) {
> + for (i = 0; i < 31; i++) {
> if (!(data->temp_mask & BIT(i + 1)))
> continue;
> if (!reg_temp_alternate[i])

Thank you for the patch. I tested that the UBSAN message is gone, and
that the module loads.

Tested-by: Paul Menzel <pmenzel+linux-hwmon@molgen.mpg.de>

Kind regards

Paul