linux-kernel - [PATCH] rtc: 88pm860x: fix unintended sign extension

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Date:   Wed,  6 Feb 2019 09:50:53 +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: 88pm860x: 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#144925-144928 ("Unintended sign extension")

Fixes: 008b30408c40 ("mfd: Add rtc support to 88pm860x")
Signed-off-by: Colin Ian King <colin.king@...onical.com>
---
 drivers/rtc/rtc-88pm860x.c | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/drivers/rtc/rtc-88pm860x.c b/drivers/rtc/rtc-88pm860x.c
index 01ffc0ef8033..d25282b4a7dd 100644
--- a/drivers/rtc/rtc-88pm860x.c
+++ b/drivers/rtc/rtc-88pm860x.c
@@ -115,11 +115,13 @@ static int pm860x_rtc_read_time(struct device *dev, struct rtc_time *tm)
 	pm860x_page_bulk_read(info->i2c, REG0_ADDR, 8, buf);
 	dev_dbg(info->dev, "%x-%x-%x-%x-%x-%x-%x-%x\n", buf[0], buf[1],
 		buf[2], buf[3], buf[4], buf[5], buf[6], buf[7]);
-	base = (buf[1] << 24) | (buf[3] << 16) | (buf[5] << 8) | buf[7];
+	base = ((unsigned long)buf[1] << 24) | (buf[3] << 16) |
+		(buf[5] << 8) | buf[7];
 
 	/* load 32-bit read-only counter */
 	pm860x_bulk_read(info->i2c, PM8607_RTC_COUNTER1, 4, buf);
-	data = (buf[3] << 24) | (buf[2] << 16) | (buf[1] << 8) | buf[0];
+	data = ((unsigned long)buf[3] << 24) | (buf[2] << 16) |
+		(buf[1] << 8) | buf[0];
 	ticks = base + data;
 	dev_dbg(info->dev, "get base:0x%lx, RO count:0x%lx, ticks:0x%lx\n",
 		base, data, ticks);
@@ -145,7 +147,8 @@ static int pm860x_rtc_set_time(struct device *dev, struct rtc_time *tm)
 
 	/* load 32-bit read-only counter */
 	pm860x_bulk_read(info->i2c, PM8607_RTC_COUNTER1, 4, buf);
-	data = (buf[3] << 24) | (buf[2] << 16) | (buf[1] << 8) | buf[0];
+	data = ((unsigned long)buf[3] << 24) | (buf[2] << 16) |
+		(buf[1] << 8) | buf[0];
 	base = ticks - data;
 	dev_dbg(info->dev, "set base:0x%lx, RO count:0x%lx, ticks:0x%lx\n",
 		base, data, ticks);
@@ -170,10 +173,12 @@ static int pm860x_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alrm)
 	pm860x_page_bulk_read(info->i2c, REG0_ADDR, 8, buf);
 	dev_dbg(info->dev, "%x-%x-%x-%x-%x-%x-%x-%x\n", buf[0], buf[1],
 		buf[2], buf[3], buf[4], buf[5], buf[6], buf[7]);
-	base = (buf[1] << 24) | (buf[3] << 16) | (buf[5] << 8) | buf[7];
+	base = ((unsigned long)buf[1] << 24) | (buf[3] << 16) |
+		(buf[5] << 8) | buf[7];
 
 	pm860x_bulk_read(info->i2c, PM8607_RTC_EXPIRE1, 4, buf);
-	data = (buf[3] << 24) | (buf[2] << 16) | (buf[1] << 8) | buf[0];
+	data = ((unsigned long)buf[3] << 24) | (buf[2] << 16) |
+		(buf[1] << 8) | buf[0];
 	ticks = base + data;
 	dev_dbg(info->dev, "get base:0x%lx, RO count:0x%lx, ticks:0x%lx\n",
 		base, data, ticks);
@@ -198,11 +203,13 @@ static int pm860x_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alrm)
 	pm860x_page_bulk_read(info->i2c, REG0_ADDR, 8, buf);
 	dev_dbg(info->dev, "%x-%x-%x-%x-%x-%x-%x-%x\n", buf[0], buf[1],
 		buf[2], buf[3], buf[4], buf[5], buf[6], buf[7]);
-	base = (buf[1] << 24) | (buf[3] << 16) | (buf[5] << 8) | buf[7];
+	base = ((unsigned long)buf[1] << 24) | (buf[3] << 16) |
+		(buf[5] << 8) | buf[7];
 
 	/* load 32-bit read-only counter */
 	pm860x_bulk_read(info->i2c, PM8607_RTC_COUNTER1, 4, buf);
-	data = (buf[3] << 24) | (buf[2] << 16) | (buf[1] << 8) | buf[0];
+	data = ((unsigned long)buf[3] << 24) | (buf[2] << 16) |
+		(buf[1] << 8) | buf[0];
 	ticks = base + data;
 	dev_dbg(info->dev, "get base:0x%lx, RO count:0x%lx, ticks:0x%lx\n",
 		base, data, ticks);
-- 
2.20.1