hwmon: (corsair-psu) fix unintentional sign extension issue

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@canonical.com>
Link: https://lore.kernel.org/r/20201105115019.41735-1-colin.king@canonical.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

diff --git a/drivers/hwmon/corsair-psu.c b/drivers/hwmon/corsair-psu.c
index e92d037..5d19a88 100644 (file)
--- 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: