[PATCH] hwmon: (nct6775) Fix access to fan pulse registers

[Guenter Roeck <linux@roeck-us.net>]

Not all fans have a fan pulse register. This can result in reading
beyond the end of REG_FAN_PULSES and FAN_PULSE_SHIFT arrays,
and was reported by smatch as possible error.

1672          for (i = 0; i < ARRAY_SIZE(data->rpm); i++) {
                              ^^^^^^^^^^^^^^^^^^^^^^^^
			      This is a 7 element array.
...
1685                  data->fan_pulses[i] =
1686                    (nct6775_read_value(data, data->REG_FAN_PULSES[i])
1687                          >> data->FAN_PULSE_SHIFT[i]) & 0x03;
                                 ^^^^^^^^^^^^^^^^^^^^^^^^
				 FAN_PULSE_SHIFT is either 5 or 6
				 elements.

To fix the problem, we have to ensure that all REG_FAN_PULSES and
FAN_PULSE_SHIFT have the appropriate length, and that REG_FAN_PULSES
is only read if the register actually exists.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
 drivers/hwmon/nct6775.c | 27 ++++++++++++++++-----------
 1 file changed, 16 insertions(+), 11 deletions(-)

diff --git a/drivers/hwmon/nct6775.c b/drivers/hwmon/nct6775.c
index 139781ae830b..87c316c6c341 100644
--- a/drivers/hwmon/nct6775.c
+++ b/drivers/hwmon/nct6775.c
@@ -299,8 +299,9 @@ static const u16 NCT6775_REG_PWM_READ[] = {
 
 static const u16 NCT6775_REG_FAN[] = { 0x630, 0x632, 0x634, 0x636, 0x638 };
 static const u16 NCT6775_REG_FAN_MIN[] = { 0x3b, 0x3c, 0x3d };
-static const u16 NCT6775_REG_FAN_PULSES[] = { 0x641, 0x642, 0x643, 0x644, 0 };
-static const u16 NCT6775_FAN_PULSE_SHIFT[] = { 0, 0, 0, 0, 0, 0 };
+static const u16 NCT6775_REG_FAN_PULSES[NUM_FAN] = {
+	0x641, 0x642, 0x643, 0x644 };
+static const u16 NCT6775_FAN_PULSE_SHIFT[NUM_FAN] = { };
 
 static const u16 NCT6775_REG_TEMP[] = {
 	0x27, 0x150, 0x250, 0x62b, 0x62c, 0x62d };
@@ -425,8 +426,8 @@ static const u8 NCT6776_PWM_MODE_MASK[] = { 0x01, 0, 0, 0, 0, 0 };
 
 static const u16 NCT6776_REG_FAN_MIN[] = {
 	0x63a, 0x63c, 0x63e, 0x640, 0x642, 0x64a, 0x64c };
-static const u16 NCT6776_REG_FAN_PULSES[] = {
-	0x644, 0x645, 0x646, 0x647, 0x648, 0x649, 0 };
+static const u16 NCT6776_REG_FAN_PULSES[NUM_FAN] = {
+	0x644, 0x645, 0x646, 0x647, 0x648, 0x649 };
 
 static const u16 NCT6776_REG_WEIGHT_DUTY_BASE[] = {
 	0x13e, 0x23e, 0x33e, 0x83e, 0x93e, 0xa3e };
@@ -502,8 +503,8 @@ static const s8 NCT6779_BEEP_BITS[] = {
 
 static const u16 NCT6779_REG_FAN[] = {
 	0x4b0, 0x4b2, 0x4b4, 0x4b6, 0x4b8, 0x4ba, 0x660 };
-static const u16 NCT6779_REG_FAN_PULSES[] = {
-	0x644, 0x645, 0x646, 0x647, 0x648, 0x649, 0 };
+static const u16 NCT6779_REG_FAN_PULSES[NUM_FAN] = {
+	0x644, 0x645, 0x646, 0x647, 0x648, 0x649 };
 
 static const u16 NCT6779_REG_CRITICAL_PWM_ENABLE[] = {
 	0x136, 0x236, 0x336, 0x836, 0x936, 0xa36, 0xb36 };
@@ -779,8 +780,8 @@ static const u16 NCT6106_REG_TEMP_CONFIG[] = {
 
 static const u16 NCT6106_REG_FAN[] = { 0x20, 0x22, 0x24 };
 static const u16 NCT6106_REG_FAN_MIN[] = { 0xe0, 0xe2, 0xe4 };
-static const u16 NCT6106_REG_FAN_PULSES[] = { 0xf6, 0xf6, 0xf6, 0, 0 };
-static const u16 NCT6106_FAN_PULSE_SHIFT[] = { 0, 2, 4, 0, 0 };
+static const u16 NCT6106_REG_FAN_PULSES[] = { 0xf6, 0xf6, 0xf6 };
+static const u16 NCT6106_FAN_PULSE_SHIFT[] = { 0, 2, 4 };
 
 static const u8 NCT6106_REG_PWM_MODE[] = { 0xf3, 0xf3, 0xf3 };
 static const u8 NCT6106_PWM_MODE_MASK[] = { 0x01, 0x02, 0x04 };
@@ -1682,9 +1683,13 @@ static struct nct6775_data *nct6775_update_device(struct device *dev)
 			if (data->has_fan_min & BIT(i))
 				data->fan_min[i] = nct6775_read_value(data,
 					   data->REG_FAN_MIN[i]);
-			data->fan_pulses[i] =
-			  (nct6775_read_value(data, data->REG_FAN_PULSES[i])
-				>> data->FAN_PULSE_SHIFT[i]) & 0x03;
+
+			if (data->REG_FAN_PULSES[i]) {
+				data->fan_pulses[i] =
+				  (nct6775_read_value(data,
+						      data->REG_FAN_PULSES[i])
+				   >> data->FAN_PULSE_SHIFT[i]) & 0x03;
+			}
 
 			nct6775_select_fan_div(dev, data, i, reg);
 		}
-- 
2.7.4