hwmon: (adm1026) Convert macros to functions to avoid TOCTOU

The macro FAN_FROM_REG evaluates its arguments multiple times. When used
in lockless contexts involving shared driver data, this causes
Time-of-Check to Time-of-Use (TOCTOU) race conditions.

Convert the macro to a static function. This guarantees that arguments
are evaluated only once (pass-by-value), preventing the race
conditions.

Adhere to the principle of minimal changes by only converting macros
that evaluate arguments multiple times and are used in lockless
contexts.

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/20251126113828.10003-1-hanguidong02@gmail.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

diff --git a/drivers/hwmon/adm1026.c b/drivers/hwmon/adm1026.c
index 80d09b017d3b73aa46a1d4bd074acb6a407609d4..c38c932e5d2af6b3812f432622c279ab4ee06b80 100644 (file)
--- a/drivers/hwmon/adm1026.c
+++ b/drivers/hwmon/adm1026.c
@@ -197,8 +197,16 @@ static int adm1026_scaling[] = { /* .001 Volts */
 #define FAN_TO_REG(val, div)  ((val) <= 0 ? 0xff : \
                                clamp_val(1350000 / ((val) * (div)), \
                                              1, 254))
-#define FAN_FROM_REG(val, div) ((val) == 0 ? -1 : (val) == 0xff ? 0 : \
-                               1350000 / ((val) * (div)))
+
+static int fan_from_reg(int val, int div)
+{
+       if (val == 0)
+               return -1;
+       if (val == 0xff)
+               return 0;
+       return 1350000 / (val * div);
+}
+
 #define DIV_FROM_REG(val) (1 << (val))
 #define DIV_TO_REG(val) ((val) >= 8 ? 3 : (val) >= 4 ? 2 : (val) >= 2 ? 1 : 0)
 
@@ -656,7 +664,7 @@ 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 adm1026_data *data = adm1026_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],
                data->fan_div[nr]));
 }
 static ssize_t fan_min_show(struct device *dev, struct device_attribute *attr,
@@ -665,7 +673,7 @@ 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 adm1026_data *data = adm1026_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],
                data->fan_div[nr]));
 }
 static ssize_t fan_min_store(struct device *dev,