[PATCH] rtc: fix rtc_time64_to_tm calculation

From: Andrzej Hajda
Date: Thu Jan 07 2016 - 07:12:21 EST


Type of local variable days has been changed recently to unsigned,
but it can take negative values. As a result it works incorrectly for some
arguments. The patch fixes it.

The problem has been detected using proposed semantic patch
scripts/coccinelle/tests/unsigned_lesser_than_zero.cocci [1].

[1]: http://permalink.gmane.org/gmane.linux.kernel/2120705

Fixes: cab572b82c4b ('rtc: fix overflow and incorrect calculation in rtc_time64_to_tm')
Signed-off-by: Andrzej Hajda <a.hajda@xxxxxxxxxxx>
---
drivers/rtc/rtc-lib.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/rtc/rtc-lib.c b/drivers/rtc/rtc-lib.c
index cf2b23c..6323d13 100644
--- a/drivers/rtc/rtc-lib.c
+++ b/drivers/rtc/rtc-lib.c
@@ -54,7 +54,7 @@ void rtc_time64_to_tm(time64_t time, struct rtc_time *tm)
{
unsigned int month, year;
int secs;
- unsigned long days;
+ unsigned long days, leaps;

/*
* time must be positive
@@ -66,13 +66,16 @@ void rtc_time64_to_tm(time64_t time, struct rtc_time *tm)
tm->tm_wday = (days + 4) % 7;

year = 1970 + days / 365;
- days -= (year - 1970) * 365
- + LEAPS_THRU_END_OF(year - 1)
- - LEAPS_THRU_END_OF(1970 - 1);
- if (days < 0) {
+ days -= (year - 1970) * 365;
+ leaps = LEAPS_THRU_END_OF(year - 1) - LEAPS_THRU_END_OF(1970 - 1);
+
+ while (days < leaps) {
year -= 1;
days += 365 + is_leap_year(year);
}
+
+ days -= leaps;
+
tm->tm_year = year - 1900;
tm->tm_yday = days + 1;

--
1.9.1

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