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rtc: Fix offset calculation for .start_secs < 0

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commit fe9f5f96cfe8b82d0f24cbfa93718925560f4f8d upstream.

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: 989515647e ("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>
Link: https://lore.kernel.org/r/20250428-enable-rtc-v4-2-2b2f7e3f9349@baylibre.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Alexandre Mergnat
2025-04-28 12:06:48 +02:00
committed by Greg Kroah-Hartman
parent b836d94be8
commit 32a5f643ce
1 changed files with 1 additions and 1 deletions
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2
drivers/rtc/class.c
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@@ -323,7 +323,7 @@ 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)