rtc: ds1672: fix unintended sign extension

BugLink: https://bugs.launchpad.net/bugs/1864773

[ Upstream commit f0c04c27 ]

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#138801 ("Unintended sign extension")

Fixes: edf1aaa3 ("[PATCH] RTC subsystem: DS1672 driver")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

drivers/rtc/rtc-ds1672.c

@@ -60,7 +60,8 @@ static int ds1672_get_datetime(struct i2c_client *client, struct rtc_time *tm)
 		"%s: raw read data - counters=%02x,%02x,%02x,%02x\n",
 		__func__, buf[0], buf[1], buf[2], buf[3]);
 
-	time = (buf[3] << 24) | (buf[2] << 16) | (buf[1] << 8) | buf[0];
+	time = ((unsigned long)buf[3] << 24) | (buf[2] << 16) |
+	       (buf[1] << 8) | buf[0];
 
 	rtc_time_to_tm(time, tm);