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: sashiko-bot@kernel.org
Closes: https://lore.kernel.org/r/20260716213252.EACA71F000E9@smtp.kernel.org
Fixes: 89fac11cb3e7 ("adt7470: make automatic fan control really work")
Signed-off-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>
Link: https://lore.kernel.org/r/20260727-adt7470_fixes-v2-3-598e38a46ba6@gmail.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

diff --git a/drivers/hwmon/adt7470.c b/drivers/hwmon/adt7470.c
index 62ec68ea0a4067fc986b909937736e6c0e1f6726..0b19b0925d1c72801f08f7efbedfb4f6df7e5da1 100644 (file)
--- 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;