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

Guenter Roeck
2018-06-13T20:47:12Z

On Wed, Jun 13, 2018 at 10:06:16PM +0200, Paul Menzel wrote:
> 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>
>
Thanks!

Guenter