hwmon: (dell-smm) Limit fan multiplier to avoid overflow

The fan nominal speed returned by SMM is limited to 16 bits, but the
driver allows the fan multiplier to be set via a module parameter.

Clamp the computed fan multiplier so that fan_nominal_speed *
i8k_fan_mult always fits into a signed 32-bit integer and refuse to
initialize the driver if the value is too large.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 20bdeeb ("hwmon: (dell-smm) Introduce helper function for data init")
Signed-off-by: Denis Sergeev <denserg.edu@gmail.com>
Link: https://lore.kernel.org/r/20251209063706.49008-1-denserg.edu@gmail.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Author: Denis Sergeev

drivers/hwmon/dell-smm-hwmon.c

@@ -76,6 +76,9 @@
 #define DELL_SMM_NO_TEMP	10
 #define DELL_SMM_NO_FANS	4
 
+/* limit fan multiplier to avoid overflow */
+#define DELL_SMM_MAX_FAN_MULT (INT_MAX / U16_MAX)
+
 struct smm_regs {
 	unsigned int eax;
 	unsigned int ebx;
@@ -1253,6 +1256,12 @@ static int dell_smm_init_data(struct device *dev, const struct dell_smm_ops *ops
 	data->ops = ops;
 	/* All options must not be 0 */
 	data->i8k_fan_mult = fan_mult ? : I8K_FAN_MULT;
+	if (data->i8k_fan_mult > DELL_SMM_MAX_FAN_MULT) {
+		dev_err(dev,
+			"fan multiplier %u is too large (max %u)\n",
+			data->i8k_fan_mult, DELL_SMM_MAX_FAN_MULT);
+		return -EINVAL;
+	}
 	data->i8k_fan_max = fan_max ? : I8K_FAN_HIGH;
 	data->i8k_pwm_mult = DIV_ROUND_UP(255, data->i8k_fan_max);