2023-05-10 14:57:51

by Nikita Zhandarovich

Subject: [PATCH] hwmon: (f71882fg) prevent possible division by zero

In the unlikely event that something goes wrong with the device and
its registers, the fan_from_reg() function may return 0. This value
will cause a division-by-zero error in the show_pwm() function.

To prevent this, test the value of
fan_from_reg(data->fan_full_speed[nr]) against 0 before performing
the division. If the division-by-zero error is avoided, assign 0 to
the val variable.

Found by Linux Verification Center (linuxtesting.org) with static
analysis tool SVACE.

Fixes: df9ec2dae094 ("hwmon: (f71882fg) Reorder symbols to get rid of a few forward declarations")
Signed-off-by: Nikita Zhandarovich <[email protected]>
---
drivers/hwmon/f71882fg.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/hwmon/f71882fg.c b/drivers/hwmon/f71882fg.c
index 70121482a617..27207ec6f7fe 100644
--- a/drivers/hwmon/f71882fg.c
+++ b/drivers/hwmon/f71882fg.c
@@ -1096,8 +1096,11 @@ static ssize_t show_pwm(struct device *dev,
val = data->pwm[nr];
else {
/* RPM mode */
- val = 255 * fan_from_reg(data->fan_target[nr])
- / fan_from_reg(data->fan_full_speed[nr]);
+ if (fan_from_reg(data->fan_full_speed[nr]))
+ val = 255 * fan_from_reg(data->fan_target[nr])
+ / fan_from_reg(data->fan_full_speed[nr]);
+ else
+ val = 0;
}
mutex_unlock(&data->update_lock);
return sprintf(buf, "%d\n", val);
--
2.25.1

2023-05-19 13:05:55

by Guenter Roeck

Subject: Re: [PATCH] hwmon: (f71882fg) prevent possible division by zero

On Wed, May 10, 2023 at 07:35:37AM -0700, Nikita Zhandarovich wrote:
> In the unlikely event that something goes wrong with the device and
> its registers, the fan_from_reg() function may return 0. This value
> will cause a division-by-zero error in the show_pwm() function.
>
> To prevent this, test the value of
> fan_from_reg(data->fan_full_speed[nr]) against 0 before performing
> the division. If the division-by-zero error is avoided, assign 0 to
> the val variable.
>
> Found by Linux Verification Center (linuxtesting.org) with static
> analysis tool SVACE.
>
> Fixes: df9ec2dae094 ("hwmon: (f71882fg) Reorder symbols to get rid of a few forward declarations")
> Signed-off-by: Nikita Zhandarovich <[email protected]>

Applied.

Thanks,
Guenter

> ---
> drivers/hwmon/f71882fg.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/hwmon/f71882fg.c b/drivers/hwmon/f71882fg.c
> index 70121482a617..27207ec6f7fe 100644
> --- a/drivers/hwmon/f71882fg.c
> +++ b/drivers/hwmon/f71882fg.c
> @@ -1096,8 +1096,11 @@ static ssize_t show_pwm(struct device *dev,
> val = data->pwm[nr];
> else {
> /* RPM mode */
> - val = 255 * fan_from_reg(data->fan_target[nr])
> - / fan_from_reg(data->fan_full_speed[nr]);
> + if (fan_from_reg(data->fan_full_speed[nr]))
> + val = 255 * fan_from_reg(data->fan_target[nr])
> + / fan_from_reg(data->fan_full_speed[nr]);
> + else
> + val = 0;
> }
> mutex_unlock(&data->update_lock);
> return sprintf(buf, "%d\n", val);