| Message ID | 20250428-enable-rtc-v4-2-2b2f7e3f9349@baylibre.com |
|---|---|
| State | Accepted |
| Headers | show |
| Series | Fix pre-1970 date handling | expand |
Hello, On Mon, Apr 28, 2025 at 12:06:48PM +0200, Alexandre Mergnat wrote: > The comparison > > rtc->start_secs > rtc->range_max > > has a signed left-hand side and an unsigned right-hand side. > So the comparison might become true for negative start_secs which is > interpreted as a (possibly very large) positive value. > > As a negative value can never be bigger than an unsigned value > the correct representation of the (mathematical) comparison > > rtc->start_secs > rtc->range_max > > in C is: > > rtc->start_secs >= 0 && rtc->start_secs > rtc->range_max > > Use that to fix the offset calculation currently used in the > rtc-mt6397 driver. > > Fixes: 989515647e783 ("rtc: Add one offset seconds to expand RTC range") > Signed-off-by: Alexandre Mergnat <amergnat@baylibre.com> Reviewed-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com> Thanks Uwe
diff --git a/drivers/rtc/class.c b/drivers/rtc/class.c index e31fa0ad127e9545afac745a621d4ccbcd5fca28..a0afdeaac270f026734be8785e8ed7e1272b2348 100644 --- a/drivers/rtc/class.c +++ b/drivers/rtc/class.c @@ -327,7 +327,7 @@ static void rtc_device_get_offset(struct rtc_device *rtc) * * Otherwise the offset seconds should be 0. */ - if (rtc->start_secs > rtc->range_max || + if ((rtc->start_secs >= 0 && rtc->start_secs > rtc->range_max) || rtc->start_secs + range_secs - 1 < rtc->range_min) rtc->offset_secs = rtc->start_secs - rtc->range_min; else if (rtc->start_secs > rtc->range_min)
The comparison rtc->start_secs > rtc->range_max has a signed left-hand side and an unsigned right-hand side. So the comparison might become true for negative start_secs which is interpreted as a (possibly very large) positive value. As a negative value can never be bigger than an unsigned value the correct representation of the (mathematical) comparison rtc->start_secs > rtc->range_max in C is: rtc->start_secs >= 0 && rtc->start_secs > rtc->range_max Use that to fix the offset calculation currently used in the rtc-mt6397 driver. Fixes: 989515647e783 ("rtc: Add one offset seconds to expand RTC range") Signed-off-by: Alexandre Mergnat <amergnat@baylibre.com> --- drivers/rtc/class.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)