[PATCH 2/3] hwmon: (isl28022) Fix integer overflow in power calculation on 32-bit

[Pradhan, Sanman]

From: Sanman Pradhan <psanman@xxxxxxxxxxx>

isl28022_read_power() computes:

  *val = ((51200000L * ((long)data->gain)) /
          (long)data->shunt) * (long)regval;

On 32-bit platforms, 'long' is 32 bits. With gain=8 and shunt=10000
(the default configuration):

  (51200000 * 8) / 10000 = 40960
  40960 * 65535 = 2,684,313,600

This exceeds LONG_MAX (2,147,483,647), resulting in signed integer
overflow.

Additionally, dividing before multiplying by regval loses precision
unnecessarily, and division on s64 requires the math64 helper on
32-bit platforms.

Use s64 intermediates with div_s64() and multiply before dividing to
retain precision. Clamp the result to LONG_MAX before returning it
through the hwmon callback, following the pattern used by ina238.

Fixes: 39671a14df4f2 ("hwmon: (isl28022) new driver for ISL28022 power monitor")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Sanman Pradhan <psanman@xxxxxxxxxxx>
---
 drivers/hwmon/isl28022.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/hwmon/isl28022.c b/drivers/hwmon/isl28022.c
index c2e559dde63f6..5d4ca1f5c5839 100644
--- a/drivers/hwmon/isl28022.c
+++ b/drivers/hwmon/isl28022.c
@@ -9,6 +9,7 @@
 #include <linux/err.h>
 #include <linux/hwmon.h>
 #include <linux/i2c.h>
+#include <linux/math64.h>
 #include <linux/module.h>
 #include <linux/regmap.h>
 
@@ -178,6 +179,7 @@ static int isl28022_read_power(struct device *dev, u32 attr, long *val)
 	struct isl28022_data *data = dev_get_drvdata(dev);
 	unsigned int regval;
 	int err;
+	s64 tmp;
 
 	switch (attr) {
 	case hwmon_power_input:
@@ -185,8 +187,9 @@ static int isl28022_read_power(struct device *dev, u32 attr, long *val)
 				  ISL28022_REG_POWER, &regval);
 		if (err < 0)
 			return err;
-		*val = ((51200000L * ((long)data->gain)) /
-			(long)data->shunt) * (long)regval;
+		tmp = (s64)51200000 * data->gain * regval;
+		tmp = div_s64(tmp, data->shunt);
+		*val = clamp_val(tmp, 0, LONG_MAX);
 		break;
 	default:
 		return -EOPNOTSUPP;
-- 
2.34.1