linux-kernel - [PATCH] rtc_time_to_tm: Fix signed / unsigned arithmetic

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Message-Id: <1217687680.3872.10.camel@bender>
Date:	Sat, 02 Aug 2008 16:34:40 +0200
From:	Jan Altenberg <jan.altenberg@...utronix.de>
To:	"Maciej W. Rozycki" <macro@...ux-mips.org>
Cc:	Linux Kernel list <linux-kernel@...r.kernel.org>,
	stable@...nel.org, tglx@...utronix.de
Subject: [PATCH] rtc_time_to_tm: Fix signed / unsigned arithmetic

Hi all,

commit 945185a69daa457c4c5e46e47f4afad7dcea734f changed the some types
in rtc_time_to_tm() to unsigned:

 void rtc_time_to_tm(unsigned long time, struct rtc_time *tm)
 {
-       register int days, month, year;
+       unsigned int days, month, year;

This doesn't work for all cases, because days is checked for < 0 later
on:

if (days < 0) {
	year -= 1;
	days += 365 + LEAP_YEAR(year);
}

I think the correct fix would be to keep days signed and do an
appropriate cast later on. See attached patch.

Signed-off-by: Jan Altenberg <jan.altenberg@...utronix.de>

---
diff --git a/drivers/rtc/rtc-lib.c b/drivers/rtc/rtc-lib.c
index 9f996ec..dd70bf7 100644
--- a/drivers/rtc/rtc-lib.c
+++ b/drivers/rtc/rtc-lib.c
@@ -51,10 +51,11 @@ EXPORT_SYMBOL(rtc_year_days);
  */
 void rtc_time_to_tm(unsigned long time, struct rtc_time *tm)
 {
-	unsigned int days, month, year;
+	unsigned int month, year;
+	int days;
 
 	days = time / 86400;
-	time -= days * 86400;
+	time -= (unsigned int) days * 86400;
 
 	/* day of the week, 1970-01-01 was a Thursday */
 	tm->tm_wday = (days + 4) % 7;


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