linux-kernel - [PATCH] rtc: tps6594: Fix integer overflow on 32bit systems

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Message-ID: <1074175e-5ecb-4e3d-b721-347d794caa90@stanley.mountain>
Date: Wed, 11 Dec 2024 12:32:34 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Esteban Blanc <eblanc@...libre.com>
Cc: Alexandre Belloni <alexandre.belloni@...tlin.com>,
	Andy Shevchenko <andy.shevchenko@...il.com>,
	linux-rtc@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: [PATCH] rtc: tps6594: Fix integer overflow on 32bit systems

The problem is this multiply in tps6594_rtc_set_offset()

	tmp = offset * TICKS_PER_HOUR;

The "tmp" variable is an s64 but "offset" is a long in the
(-277774)-277774 range.  On 32bit systems a long can hold numbers up to
approximately two billion.  The number of TICKS_PER_HOUR is really large,
(32768 * 3600) or roughly a hundred million.  When you start multiplying
by a hundred million it doesn't take long to overflow the two billion
mark.

Probably the safest way to fix this is to change the type of
TICKS_PER_HOUR to long long because it's such a large number.

Fixes: 9f67c1e63976 ("rtc: tps6594: Add driver for TPS6594 RTC")
Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>
---
 drivers/rtc/rtc-tps6594.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/rtc/rtc-tps6594.c b/drivers/rtc/rtc-tps6594.c
index e69667634137..7c6246e3f029 100644
--- a/drivers/rtc/rtc-tps6594.c
+++ b/drivers/rtc/rtc-tps6594.c
@@ -37,7 +37,7 @@
 #define MAX_OFFSET (277774)
 
 // Number of ticks per hour
-#define TICKS_PER_HOUR (32768 * 3600)
+#define TICKS_PER_HOUR (32768 * 3600LL)
 
 // Multiplier for ppb conversions
 #define PPB_MULT NANO
-- 
2.45.2