[PATCH] rtc: Fix overflow when converting time64_t to rtc_time

From: Baolin Wang
Date: Mon Dec 25 2017 - 06:11:58 EST


If we convert one large time values to rtc_time, in the original formula
'days * 86400' can be overflowed in 'unsigned int' type to make the formula
get one incorrect remain seconds value. Thus we can use div_s64_rem()
function to avoid this situation.

Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxx>
---
drivers/rtc/rtc-lib.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/rtc/rtc-lib.c b/drivers/rtc/rtc-lib.c
index 1ae7da5..ad5bb21 100644
--- a/drivers/rtc/rtc-lib.c
+++ b/drivers/rtc/rtc-lib.c
@@ -52,13 +52,11 @@ int rtc_year_days(unsigned int day, unsigned int month, unsigned int year)
*/
void rtc_time64_to_tm(time64_t time, struct rtc_time *tm)
{
- unsigned int month, year;
- unsigned long secs;
+ unsigned int month, year, secs;
int days;

/* time must be positive */
- days = div_s64(time, 86400);
- secs = time - (unsigned int) days * 86400;
+ days = div_s64_rem(time, 86400, &secs);

/* day of the week, 1970-01-01 was a Thursday */
tm->tm_wday = (days + 4) % 7;
--
1.7.9.5