[PATCH AUTOSEL 5.4 169/330] media: tda10071: fix unsigned sign extension overflow

Sasha Levin
2020-09-18T03:04:56Z

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

[ Upstream commit a7463e2dc698075132de9905b89f495df888bb79 ]

The shifting of buf[3] by 24 bits to the left will be promoted to
a 32 bit signed int and then sign-extended to an unsigned long. In
the unlikely event that the the top bit of buf[3] is set then all
then all the upper bits end up as also being set because of
the sign-extension and this affect the ev->post_bit_error sum.
Fix this by using the temporary u32 variable bit_error to avoid
the sign-extension promotion. This also removes the need to do the
computation twice.

Addresses-Coverity: ("Unintended sign extension")

Fixes: 267897a4708f ("[media] tda10071: implement DVBv5 statistics")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/media/dvb-frontends/tda10071.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/media/dvb-frontends/tda10071.c b/drivers/media/dvb-frontends/tda10071.c
index 1953b00b3e487..685c0ac71819e 100644
--- a/drivers/media/dvb-frontends/tda10071.c
+++ b/drivers/media/dvb-frontends/tda10071.c
@@ -470,10 +470,11 @@ static int tda10071_read_status(struct dvb_frontend *fe, enum fe_status *status)
goto error;

if (dev->delivery_system == SYS_DVBS) {
- dev->dvbv3_ber = buf[0] << 24 | buf[1] << 16 |
- buf[2] << 8 | buf[3] << 0;
- dev->post_bit_error += buf[0] << 24 | buf[1] << 16 |
- buf[2] << 8 | buf[3] << 0;
+ u32 bit_error = buf[0] << 24 | buf[1] << 16 |
+ buf[2] << 8 | buf[3] << 0;
+
+ dev->dvbv3_ber = bit_error;
+ dev->post_bit_error += bit_error;
c->post_bit_error.stat[0].scale = FE_SCALE_COUNTER;
c->post_bit_error.stat[0].uvalue = dev->post_bit_error;
dev->block_error += buf[4] << 8 | buf[5] << 0;
--
2.25.1