* [PATCH] media: tda10071: fix unsigned sign extension overflow
@ 2020-02-10 14:26 Colin King
2020-02-10 14:41 ` Dan Carpenter
0 siblings, 1 reply; 2+ messages in thread
From: Colin King @ 2020-02-10 14:26 UTC (permalink / raw)
To: Antti Palosaari, Mauro Carvalho Chehab, linux-media
Cc: kernel-janitors, linux-kernel
From: Colin Ian King <colin.king@canonical.com>
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>
---
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 1953b00b3e48..685c0ac71819 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;
--
2.25.0
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] media: tda10071: fix unsigned sign extension overflow
2020-02-10 14:26 [PATCH] media: tda10071: fix unsigned sign extension overflow Colin King
@ 2020-02-10 14:41 ` Dan Carpenter
0 siblings, 0 replies; 2+ messages in thread
From: Dan Carpenter @ 2020-02-10 14:41 UTC (permalink / raw)
To: Colin King
Cc: Antti Palosaari, Mauro Carvalho Chehab, linux-media,
kernel-janitors, linux-kernel
On Mon, Feb 10, 2020 at 02:26:46PM +0000, Colin King wrote:
> From: Colin Ian King <colin.king@canonical.com>
>
> 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>
> ---
> 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 1953b00b3e48..685c0ac71819 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;
This driver has a bunch of endian conversions (probably from big endian
to little endian) and so it's probably buggy on big endian CPUs.
regards,
dan carpenter
^ permalink raw reply [flat|nested] 2+ messages in thread
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