linux-kernel - [PATCH][next] hwmon: corsair-psu: fix unintentional sign extension issue

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Message-Id: <20201105115019.41735-1-colin.king@canonical.com>
Date:   Thu,  5 Nov 2020 11:50:19 +0000
From:   Colin King <colin.king@...onical.com>
To:     Wilken Gottwalt <wilken.gottwalt@...teo.net>,
        Jean Delvare <jdelvare@...e.com>,
        Guenter Roeck <linux@...ck-us.net>, linux-hwmon@...r.kernel.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH][next] hwmon: corsair-psu: fix unintentional sign extension issue

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

The shifting of the u8 integer data[3] by 24 bits to the left will
be promoted to a 32 bit signed int and then sign-extended to a
long. In the event that the top bit of data[3] is set then all
then all the upper 32 bits of a 64 bit long end up as also being
set because of the sign-extension. Fix this by casting data[3] to
a long before the shift.

Addresses-Coverity: ("Unintended sign extension")
Fixes: ce15cd2cee8b ("hwmon: add Corsair PSU HID controller driver")
Signed-off-by: Colin Ian King <colin.king@...onical.com>
---
 drivers/hwmon/corsair-psu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/hwmon/corsair-psu.c b/drivers/hwmon/corsair-psu.c
index e92d0376e7ac..5d19a888231a 100644
--- a/drivers/hwmon/corsair-psu.c
+++ b/drivers/hwmon/corsair-psu.c
@@ -241,7 +241,7 @@ static int corsairpsu_get_value(struct corsairpsu_data *priv, u8 cmd, u8 rail, l
 	 * the LINEAR11 conversion are the watts values which are about 1200 for the strongest psu
 	 * supported (HX1200i)
 	 */
-	tmp = (data[3] << 24) + (data[2] << 16) + (data[1] << 8) + data[0];
+	tmp = ((long)data[3] << 24) + (data[2] << 16) + (data[1] << 8) + data[0];
 	switch (cmd) {
 	case PSU_CMD_IN_VOLTS:
 	case PSU_CMD_IN_AMPS:
-- 
2.27.0