iio: health: afe4404: Fix oob read in afe4404_[read|write]_raw

KASAN report out-of-bounds read as follows:

BUG: KASAN: global-out-of-bounds in afe4404_read_raw+0x2ce/0x380
Read of size 4 at addr ffffffffc00e4658 by task cat/278

Call Trace:
 afe4404_read_raw
 iio_read_channel_info
 dev_attr_show

The buggy address belongs to the variable:
 afe4404_channel_leds+0x18/0xffffffffffffe9c0

This issue can be reproduce by singe command:

 $ cat /sys/bus/i2c/devices/0-0058/iio\:device0/in_intensity6_raw

The array size of afe4404_channel_leds and afe4404_channel_offdacs
are less than channels, so access with chan->address cause OOB read
in afe4404_[read|write]_raw. Fix it by moving access before use them.

Fixes: b36e825 ("iio: health/afe440x: Use regmap fields")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Acked-by: Andrew Davis <afd@ti.com>
Link: https://lore.kernel.org/r/20221107152010.95937-1-weiyongjun@huaweicloud.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Author: Wei Yongjun

drivers/iio/health/afe4404.c

@@ -250,20 +250,20 @@ static int afe4404_read_raw(struct iio_dev *indio_dev,
 			    int *val, int *val2, long mask)
 {
 	struct afe4404_data *afe = iio_priv(indio_dev);
-	unsigned int value_reg = afe4404_channel_values[chan->address];
-	unsigned int led_field = afe4404_channel_leds[chan->address];
-	unsigned int offdac_field = afe4404_channel_offdacs[chan->address];
+	unsigned int value_reg, led_field, offdac_field;
 	int ret;
 
 	switch (chan->type) {
 	case IIO_INTENSITY:
 		switch (mask) {
 		case IIO_CHAN_INFO_RAW:
+			value_reg = afe4404_channel_values[chan->address];
 			ret = regmap_read(afe->regmap, value_reg, val);
 			if (ret)
 				return ret;
 			return IIO_VAL_INT;
 		case IIO_CHAN_INFO_OFFSET:
+			offdac_field = afe4404_channel_offdacs[chan->address];
 			ret = regmap_field_read(afe->fields[offdac_field], val);
 			if (ret)
 				return ret;
@@ -273,6 +273,7 @@ static int afe4404_read_raw(struct iio_dev *indio_dev,
 	case IIO_CURRENT:
 		switch (mask) {
 		case IIO_CHAN_INFO_RAW:
+			led_field = afe4404_channel_leds[chan->address];
 			ret = regmap_field_read(afe->fields[led_field], val);
 			if (ret)
 				return ret;
@@ -295,19 +296,20 @@ static int afe4404_write_raw(struct iio_dev *indio_dev,
 			     int val, int val2, long mask)
 {
 	struct afe4404_data *afe = iio_priv(indio_dev);
-	unsigned int led_field = afe4404_channel_leds[chan->address];
-	unsigned int offdac_field = afe4404_channel_offdacs[chan->address];
+	unsigned int led_field, offdac_field;
 
 	switch (chan->type) {
 	case IIO_INTENSITY:
 		switch (mask) {
 		case IIO_CHAN_INFO_OFFSET:
+			offdac_field = afe4404_channel_offdacs[chan->address];
 			return regmap_field_write(afe->fields[offdac_field], val);
 		}
 		break;
 	case IIO_CURRENT:
 		switch (mask) {
 		case IIO_CHAN_INFO_RAW:
+			led_field = afe4404_channel_leds[chan->address];
 			return regmap_field_write(afe->fields[led_field], val);
 		}
 		break;