[PATCH v2 3/6] hwmon: (adt7470) Fix busy-loop and I2C flooding in update thread

When userspace configures 'auto_update_interval' to 0 via sysfs, the
background kthread executes schedule_timeout_interruptible(0), which
returns immediately.

If 'num_temp_sensors' is concurrently or previously set to 0, the
msleep_interruptible() delay inside adt7470_read_temperatures() also
becomes 0. This combination forces the background thread into a tight,
unbounded busy-loop, hogging the CPU and flooding the I2C bus with a
continuous stream of transactions.

Fix this vulnerability by raising the lower limit of the clamp_val in
auto_update_interval_store() from 0 to 500 milliseconds. This guarantees
a reasonable minimum sleep window between sensor updates, protecting the
system from intentional or accidental I2C bus denial of service.

Reported-by: [email protected]
Closes: https://lore.kernel.org/r/[email protected]
Fixes: 89fac11cb3e7 ("adt7470: make automatic fan control really work")
Signed-off-by: Luiz Angelo Daros de Luca <[email protected]>
---
 drivers/hwmon/adt7470.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/hwmon/adt7470.c b/drivers/hwmon/adt7470.c
index 481d51617f4b..77e7be692790 100644
--- a/drivers/hwmon/adt7470.c
+++ b/drivers/hwmon/adt7470.c
@@ -509,7 +509,7 @@ static ssize_t auto_update_interval_store(struct device *dev,
 	if (kstrtol(buf, 10, &temp))
 		return -EINVAL;
 
-	temp = clamp_val(temp, 0, 60000);
+	temp = clamp_val(temp, 500, 60000);
 
 	mutex_lock(&data->lock);
 	data->auto_update_interval = temp;

-- 
2.55.0