[PATCH] hwmon: Fix potential UAF in pec_store

[Guenter Roeck <linux@roeck-us.net>]

Sashiko reports:

In pec_store(), a guard(mutex)(&hwdev->lock) is taken. If the chip write
operation returns an error other than -EOPNOTSUPP, the code jumps to the
put label, which calls put_device(hdev). If this drops the final reference,
the device is freed. When the function then returns, the guard cleanup
function runs and attempts to unlock the freed mutex.

Use scoped_guard() instead of guard() to avoid the problem.

Fixes: 3ad2a7b9b15d5 ("hwmon: Serialize accesses in hwmon core")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
 drivers/hwmon/hwmon.c | 21 ++++++++++-----------
 1 file changed, 10 insertions(+), 11 deletions(-)

diff --git a/drivers/hwmon/hwmon.c b/drivers/hwmon/hwmon.c
index 41755910a25a..3e65fc6d25eb 100644
--- a/drivers/hwmon/hwmon.c
+++ b/drivers/hwmon/hwmon.c
@@ -371,18 +371,17 @@ static ssize_t pec_store(struct device *dev, const struct device_attribute *deva
 	 * handling is not required.
 	 */
 	hwdev = to_hwmon_device(hdev);
-	guard(mutex)(&hwdev->lock);
-	if (hwdev->chip->ops->write) {
-		err = hwdev->chip->ops->write(hdev, hwmon_chip, hwmon_chip_pec, 0, val);
-		if (err && err != -EOPNOTSUPP)
-			goto put;
+	scoped_guard(mutex, &hwdev->lock) {
+		if (hwdev->chip->ops->write) {
+			err = hwdev->chip->ops->write(hdev, hwmon_chip, hwmon_chip_pec, 0, val);
+			if (err && err != -EOPNOTSUPP)
+				goto put;
+		}
+		if (!val)
+			client->flags &= ~I2C_CLIENT_PEC;
+		else
+			client->flags |= I2C_CLIENT_PEC;
 	}
-
-	if (!val)
-		client->flags &= ~I2C_CLIENT_PEC;
-	else
-		client->flags |= I2C_CLIENT_PEC;
-
 	err = count;
 put:
 	put_device(hdev);
-- 
2.45.2