linux-kernel - [PATCH] rtc: pm8xxx: fix unintended sign extension

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Message-Id: <20190206103102.19345-1-colin.king@canonical.com>
Date:   Wed,  6 Feb 2019 10:31:02 +0000
From:   Colin King <colin.king@...onical.com>
To:     Alessandro Zummo <a.zummo@...ertech.it>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        linux-rtc@...r.kernel.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] rtc: pm8xxx: fix unintended sign extension

From: Colin Ian King <colin.king@...onical.com>

Shifting a u8 by 24 will cause the value to be promoted to an integer. If
the top bit of the u8 is set then the following conversion to an unsigned
long will sign extend the value causing the upper 32 bits to be set in
the result.

Fix this by casting the u8 value to an unsigned long before the shift.

Detected by CoverityScan, CID#1309693 ("Unintended sign extension")

Fixes: 9a9a54ad7aa2 ("drivers/rtc: add support for Qualcomm PMIC8xxx RTC")
Signed-off-by: Colin Ian King <colin.king@...onical.com>
---
 drivers/rtc/rtc-pm8xxx.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/rtc/rtc-pm8xxx.c b/drivers/rtc/rtc-pm8xxx.c
index 1074e3dbfc1d..cda020700744 100644
--- a/drivers/rtc/rtc-pm8xxx.c
+++ b/drivers/rtc/rtc-pm8xxx.c
@@ -213,7 +213,8 @@ static int pm8xxx_rtc_read_time(struct device *dev, struct rtc_time *tm)
 		}
 	}
 
-	secs = value[0] | (value[1] << 8) | (value[2] << 16) | (value[3] << 24);
+	secs = value[0] | (value[1] << 8) | (value[2] << 16) |
+	       ((unsigned long)value[3] << 24);
 
 	rtc_time_to_tm(secs, tm);
 
@@ -284,7 +285,8 @@ static int pm8xxx_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alarm)
 		return rc;
 	}
 
-	secs = value[0] | (value[1] << 8) | (value[2] << 16) | (value[3] << 24);
+	secs = value[0] | (value[1] << 8) | (value[2] << 16) |
+	       ((unsigned long)value[3] << 24);
 
 	rtc_time_to_tm(secs, &alarm->time);
 
-- 
2.20.1