[PATCH v5 1/5] hwmon: (aquacomputer_d5next) Avoid truncating scaled sensor readings

[Vas Zayarskiy]

High Flow Next power is reported in watts. Multiplying the 16-bit value
by one million can overflow both the signed intermediate and the u32
cache. Store power in long, perform the conversion in u64, and clamp to
LONG_MAX. The other existing power conversions fit in a signed 32-bit
value. Return -ENODATA for unavailable power instead of exposing the
stored error as a reading.

The power cache is updated by HID reports without the hwmon read mutex.
Read it once with READ_ONCE() and use that snapshot for both the
availability check and the returned value. Mark the corresponding
updates with WRITE_ONCE() so that the shared accesses are explicit.

Widen the shared current cache to u32. The Aquastream XT conversion to
milliamperes can exceed 65535 mA; clamp its negative conversion results
to zero before assigning to the unsigned cache. This also permits devices
with scaled aggregate currents to store milliamperes directly.

Assisted-by: LLM sparse
Signed-off-by: Vas Zayarskiy <contact@xxxxxxxxx>
---
Changes in v5: Snapshot the power cache once for validation and output,
and mark power-cache writes with WRITE_ONCE().

 drivers/hwmon/aquacomputer_d5next.c | 29 ++++++++++++++++++-----------
 1 file changed, 18 insertions(+), 11 deletions(-)

diff --git a/drivers/hwmon/aquacomputer_d5next.c b/drivers/hwmon/aquacomputer_d5next.c
index 1ca70e726..33d292228 100644
--- a/drivers/hwmon/aquacomputer_d5next.c
+++ b/drivers/hwmon/aquacomputer_d5next.c
@@ -19,6 +19,7 @@
 #include <linux/hwmon.h>
 #include <linux/jiffies.h>
 #include <linux/ktime.h>
+#include <linux/limits.h>
 #include <linux/module.h>
 #include <linux/seq_file.h>
 #include <linux/unaligned.h>
@@ -599,9 +600,9 @@ struct aqc_data {
 	u32 speed_input_min[1];
 	u32 speed_input_target[1];
 	u32 speed_input_max[1];
-	u32 power_input[8];
+	long power_input[8];
 	u16 voltage_input[8];
-	u16 current_input[8];
+	u32 current_input[8];
 
 	/* Label values */
 	const char *const *temp_label;
@@ -976,7 +977,7 @@ static int aqc_legacy_read(struct aqc_data *priv)
 
 		/* Calculation derived from linear regression */
 		sensor_value = get_unaligned_le16(priv->buffer + AQUASTREAMXT_PUMP_CURR_OFFSET);
-		priv->current_input[0] = DIV_ROUND_CLOSEST(sensor_value * 176, 100) - 52;
+		priv->current_input[0] = max(DIV_ROUND_CLOSEST(sensor_value * 176, 100) - 52, 0);
 
 		sensor_value = get_unaligned_le16(priv->buffer + AQUASTREAMXT_PUMP_VOLTAGE_OFFSET);
 		priv->voltage_input[0] = DIV_ROUND_CLOSEST(sensor_value * 1000, 61);
@@ -1006,6 +1007,7 @@ static int aqc_legacy_read(struct aqc_data *priv)
 static int aqc_read(struct device *dev, enum hwmon_sensor_types type, u32 attr,
 		    int channel, long *val)
 {
+	long power;
 	int ret;
 	struct aqc_data *priv = dev_get_drvdata(dev);
 
@@ -1070,7 +1072,10 @@ static int aqc_read(struct device *dev, enum hwmon_sensor_types type, u32 attr,
 		}
 		break;
 	case hwmon_power:
-		*val = priv->power_input[channel];
+		power = READ_ONCE(priv->power_input[channel]);
+		if (power == -ENODATA)
+			return -ENODATA;
+		*val = power;
 		break;
 	case hwmon_pwm:
 		switch (priv->kind) {
@@ -1368,9 +1373,9 @@ static int aqc_raw_event(struct hid_device *hdev, struct hid_report *report, u8
 		priv->speed_input[i] =
 		    get_unaligned_be16(data + priv->fan_sensor_offsets[i] +
 				       priv->fan_structure->speed);
-		priv->power_input[i] =
-		    get_unaligned_be16(data + priv->fan_sensor_offsets[i] +
-				       priv->fan_structure->power) * 10000;
+		WRITE_ONCE(priv->power_input[i],
+			   get_unaligned_be16(data + priv->fan_sensor_offsets[i] +
+					      priv->fan_structure->power) * 10000);
 		priv->voltage_input[i] =
 		    get_unaligned_be16(data + priv->fan_sensor_offsets[i] +
 				       priv->fan_structure->voltage) * 10;
@@ -1410,7 +1415,8 @@ static int aqc_raw_event(struct hid_device *hdev, struct hid_report *report, u8
 		priv->speed_input[2] = get_unaligned_be16(data + AQUASTREAMULT_PRESSURE_OFFSET);
 		priv->speed_input[3] = get_unaligned_be16(data + AQUASTREAMULT_FLOW_SENSOR_OFFSET);
 
-		priv->power_input[1] = get_unaligned_be16(data + AQUASTREAMULT_PUMP_POWER) * 10000;
+		WRITE_ONCE(priv->power_input[1],
+			   get_unaligned_be16(data + AQUASTREAMULT_PUMP_POWER) * 10000);
 
 		priv->voltage_input[1] = get_unaligned_be16(data + AQUASTREAMULT_PUMP_VOLTAGE) * 10;
 
@@ -1423,10 +1429,11 @@ static int aqc_raw_event(struct hid_device *hdev, struct hid_report *report, u8
 	case highflownext:
 		/* If external temp sensor is not connected, its power reading is also N/A */
 		if (priv->temp_input[1] == -ENODATA)
-			priv->power_input[0] = -ENODATA;
+			WRITE_ONCE(priv->power_input[0], -ENODATA);
 		else
-			priv->power_input[0] =
-			    get_unaligned_be16(data + HIGHFLOWNEXT_POWER) * 1000000;
+			WRITE_ONCE(priv->power_input[0],
+				   min_t(u64, get_unaligned_be16(data + HIGHFLOWNEXT_POWER) *
+					 1000000ULL, LONG_MAX));
 
 		priv->voltage_input[0] = get_unaligned_be16(data + HIGHFLOWNEXT_5V_VOLTAGE) * 10;
 		priv->voltage_input[1] =