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hwmon: (vt8231) Convert macros to functions to avoid TOCTOU 

The macro FAN_FROM_REG evaluates its arguments multiple times. When used
with shared driver data, this leads to Time-of-Check to Time-of-Use
(TOCTOU) race conditions, potentially causing divide-by-zero errors.

Convert the macro to a static function to ensure arguments are evaluated
only once.

Additionally, in fan_div_store, move the reading of the old register
value and the calculation of the minimum limit inside the update lock.
This ensures that the read-modify-write sequence operates on consistent
data, preventing race conditions during fan divider updates.

Link: https://lore.kernel.org/all/CALbr=LYJ_ehtp53HXEVkSpYoub+XYSTU8Rg=o1xxMJ8=5z8B-g@mail.gmail.com/
Signed-off-by: Gui-Dong Han <hanguidong02@gmail.com>
Link: https://lore.kernel.org/r/20251124165900.4713-1-hanguidong02@gmail.com
[groeck: Dropped unnecessary line split]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
pull/1354/merge
Gui-Dong Han 2025-11-25 00:59:00 +08:00 committed by Guenter Roeck
parent 4faaa77d6b
commit fe598ab37e
1 changed files with 12 additions and 6 deletions
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18
drivers/hwmon/vt8231.c
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@ -138,7 +138,12 @@ static inline u8 FAN_TO_REG(long rpm, int div)
return clamp_val(1310720 / (rpm * div), 1, 255);
}
#define FAN_FROM_REG(val, div) ((val) == 0 ? 0 : 1310720 / ((val) * (div)))
static int fan_from_reg(int val, int div)
{
if (val == 0)
return 0;
return 1310720 / (val * div);
}
struct vt8231_data {
unsigned short addr;
@ -561,7 +566,7 @@ static ssize_t fan_show(struct device *dev, struct device_attribute *attr,
struct sensor_device_attribute *sensor_attr = to_sensor_dev_attr(attr);
int nr = sensor_attr->index;
struct vt8231_data *data = vt8231_update_device(dev);
return sprintf(buf, "%d\n", FAN_FROM_REG(data->fan[nr],
return sprintf(buf, "%d\n", fan_from_reg(data->fan[nr],
DIV_FROM_REG(data->fan_div[nr])));
}
@ -571,7 +576,7 @@ static ssize_t fan_min_show(struct device *dev, struct device_attribute *attr,
struct sensor_device_attribute *sensor_attr = to_sensor_dev_attr(attr);
int nr = sensor_attr->index;
struct vt8231_data *data = vt8231_update_device(dev);
return sprintf(buf, "%d\n", FAN_FROM_REG(data->fan_min[nr],
return sprintf(buf, "%d\n", fan_from_reg(data->fan_min[nr],
DIV_FROM_REG(data->fan_div[nr])));
}
@ -613,9 +618,8 @@ static ssize_t fan_div_store(struct device *dev,
struct sensor_device_attribute *sensor_attr = to_sensor_dev_attr(attr);
unsigned long val;
int nr = sensor_attr->index;
int old = vt8231_read_value(data, VT8231_REG_FANDIV);
long min = FAN_FROM_REG(data->fan_min[nr],
DIV_FROM_REG(data->fan_div[nr]));
int old;
long min;
int err;
err = kstrtoul(buf, 10, &val);
@ -623,6 +627,8 @@ static ssize_t fan_div_store(struct device *dev,
return err;
mutex_lock(&data->update_lock);
old = vt8231_read_value(data, VT8231_REG_FANDIV);
min = fan_from_reg(data->fan_min[nr], DIV_FROM_REG(data->fan_div[nr]));
switch (val) {
case 1:
data->fan_div[nr] = 0;