staging: iio: ade7759: fix signed extension bug on shift of a u8

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@canonical.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/staging/iio/meter/ade7759.c b/drivers/staging/iio/meter/ade7759.c
index b691f10..60376d3 100644 (file)
--- 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(struct device *dev,
                                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: