linux-kernel - [PATCH] rtc: fix rtc_time64_to

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Date:	Thu, 07 Jan 2016 13:11:50 +0100
From:	Andrzej Hajda <a.hajda@...sung.com>
To:	Alessandro Zummo <a.zummo@...ertech.it>,
	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	rtc-linux@...glegroups.com (open list:REAL TIME CLOCK (RTC) SUBSYSTEM)
Cc:	Andrzej Hajda <a.hajda@...sung.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	linux-kernel@...r.kernel.org (open list)
Subject: [PATCH] rtc: fix rtc_time64_to_tm calculation

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@...sung.com>
---
 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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