[PATCH v3] iio: health: afe4403: Fix oob read in afe4403_read_raw

[Wei Yongjun <weiyongjun@huaweicloud.com>]

From: Wei Yongjun <weiyongjun1@huawei.com>

KASAN report out-of-bounds read as follows:

BUG: KASAN: global-out-of-bounds in afe4403_read_raw+0x42e/0x4c0
Read of size 4 at addr ffffffffc02ac638 by task cat/279

Call Trace:
 afe4403_read_raw
 iio_read_channel_info
 dev_attr_show

The buggy address belongs to the variable:
 afe4403_channel_leds+0x18/0xffffffffffffe9e0

This issue can be reproduced by singe command:

 $ cat /sys/bus/spi/devices/spi0.0/iio\:device0/in_intensity6_raw

The array size of afe4403_channel_leds is less than channels, so access
with chan->address cause OOB read in afe4403_read_raw. Fix it by moving
access before use it.

Fixes: b36e8257641a ("iio: health/afe440x: Use regmap fields")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Acked-by: Andrew Davis <afd@ti.com>
---
v2 -> v3: re-format backtraces
v1 -> v2: also moved 'reg' to right before we use it
          added Acked-by

 drivers/iio/health/afe4403.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/iio/health/afe4403.c b/drivers/iio/health/afe4403.c
index 3bb4028c5d74..df3bc5c3d378 100644
--- a/drivers/iio/health/afe4403.c
+++ b/drivers/iio/health/afe4403.c
@@ -245,14 +245,14 @@ static int afe4403_read_raw(struct iio_dev *indio_dev,
 			    int *val, int *val2, long mask)
 {
 	struct afe4403_data *afe = iio_priv(indio_dev);
-	unsigned int reg = afe4403_channel_values[chan->address];
-	unsigned int field = afe4403_channel_leds[chan->address];
+	unsigned int reg, field;
 	int ret;
 
 	switch (chan->type) {
 	case IIO_INTENSITY:
 		switch (mask) {
 		case IIO_CHAN_INFO_RAW:
+			reg = afe4403_channel_values[chan->address];
 			ret = afe4403_read(afe, reg, val);
 			if (ret)
 				return ret;
@@ -262,6 +262,7 @@ static int afe4403_read_raw(struct iio_dev *indio_dev,
 	case IIO_CURRENT:
 		switch (mask) {
 		case IIO_CHAN_INFO_RAW:
+			field = afe4403_channel_leds[chan->address];
 			ret = regmap_field_read(afe->fields[field], val);
 			if (ret)
 				return ret;
-- 
2.34.1