[PATCH] hwmon: (w83l786ng) Convert macros to functions to avoid TOCTOU

[Gui-Dong Han <hanguidong02@gmail.com>]

The macros FAN_FROM_REG and TEMP_FROM_REG evaluate their 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 macros to static functions. 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/
Fixes: 85f03bccd6e0 ("hwmon: Add support for Winbond W83L786NG/NR")
Cc: stable@vger.kernel.org
Signed-off-by: Gui-Dong Han <hanguidong02@gmail.com>
---
Based on the discussion in the link, I will submit a series of patches to
address TOCTOU issues in the hwmon subsystem by converting macros to
functions or adjusting locking where appropriate.
---
 drivers/hwmon/w83l786ng.c | 26 ++++++++++++++++++--------
 1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/drivers/hwmon/w83l786ng.c b/drivers/hwmon/w83l786ng.c
index 9b81bd406e05..1d9109ca1585 100644
--- a/drivers/hwmon/w83l786ng.c
+++ b/drivers/hwmon/w83l786ng.c
@@ -76,15 +76,25 @@ FAN_TO_REG(long rpm, int div)
 	return clamp_val((1350000 + rpm * div / 2) / (rpm * div), 1, 254);
 }
 
-#define FAN_FROM_REG(val, div)	((val) == 0   ? -1 : \
-				((val) == 255 ? 0 : \
-				1350000 / ((val) * (div))))
+static int fan_from_reg(int val, int div)
+{
+	if (val == 0)
+		return -1;
+	if (val == 255)
+		return 0;
+	return 1350000 / (val * div);
+}
 
 /* for temp */
 #define TEMP_TO_REG(val)	(clamp_val(((val) < 0 ? (val) + 0x100 * 1000 \
 						      : (val)) / 1000, 0, 0xff))
-#define TEMP_FROM_REG(val)	(((val) & 0x80 ? \
-				  (val) - 0x100 : (val)) * 1000)
+
+static int temp_from_reg(int val)
+{
+	if (val & 0x80)
+		return (val - 0x100) * 1000;
+	return val * 1000;
+}
 
 /*
  * The analog voltage inputs have 8mV LSB. Since the sysfs output is
@@ -280,7 +290,7 @@ static ssize_t show_##reg(struct device *dev, struct device_attribute *attr, \
 	int nr = to_sensor_dev_attr(attr)->index; \
 	struct w83l786ng_data *data = w83l786ng_update_device(dev); \
 	return sprintf(buf, "%d\n", \
-		FAN_FROM_REG(data->reg[nr], DIV_FROM_REG(data->fan_div[nr]))); \
+		fan_from_reg(data->reg[nr], DIV_FROM_REG(data->fan_div[nr]))); \
 }
 
 show_fan_reg(fan);
@@ -347,7 +357,7 @@ store_fan_div(struct device *dev, struct device_attribute *attr,
 
 	/* Save fan_min */
 	mutex_lock(&data->update_lock);
-	min = FAN_FROM_REG(data->fan_min[nr], DIV_FROM_REG(data->fan_div[nr]));
+	min = fan_from_reg(data->fan_min[nr], DIV_FROM_REG(data->fan_div[nr]));
 
 	data->fan_div[nr] = DIV_TO_REG(val);
 
@@ -409,7 +419,7 @@ show_temp(struct device *dev, struct device_attribute *attr, char *buf)
 	int nr = sensor_attr->nr;
 	int index = sensor_attr->index;
 	struct w83l786ng_data *data = w83l786ng_update_device(dev);
-	return sprintf(buf, "%d\n", TEMP_FROM_REG(data->temp[nr][index]));
+	return sprintf(buf, "%d\n", temp_from_reg(data->temp[nr][index]));
 }
 
 static ssize_t
-- 
2.43.0