[PATCH 3.2 34/94] staging: iio: ade7759: fix signed extension bug on shift of a u8

[Ben Hutchings]

3.2.97-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Colin Ian King <colin.king@xxxxxxxxxxxxx>

commit 13ffe9a26df4e156363579b25c904dd0b1e31bfb upstream.

The current shift of st->rx[2] left shifts a u8 24 bits left,
promotes the integer to a an int and then to a unsigned u64. If
the top bit of st->rx[2] is set then we end up with all the upper
bits being set to 1. Fix this by casting st->rx[2] to a u64 before
the 24 bit left shift.

Detected by CoverityScan CID#144940 ("Unintended sign extension")

Fixes: 2919fa54ef64 ("staging: iio: meter: new driver for ADE7759 devices")
Signed-off-by: Colin Ian King <colin.king@xxxxxxxxxxxxx>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/staging/iio/meter/ade7759.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/staging/iio/meter/ade7759.c
+++ b/drivers/staging/iio/meter/ade7759.c
@@ -128,7 +128,7 @@ static int ade7759_spi_read_reg_40(struc
 				reg_address);
 		goto error_ret;
 	}
-	*val = ((u64)st->rx[1] << 32) | (st->rx[2] << 24) |
+	*val = ((u64)st->rx[1] << 32) | ((u64)st->rx[2] << 24) |
 		(st->rx[3] << 16) | (st->rx[4] << 8) | st->rx[5];
 
 error_ret: