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 <n.zhandarovich@fintech.ru>
Link: https://lore.kernel.org/r/20230510143537.145060-1-n.zhandarovich@fintech.ru
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

diff --git a/drivers/hwmon/f71882fg.c b/drivers/hwmon/f71882fg.c
index 7012148..27207ec 100644 (file)
--- 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);