[PATCH v2] iio: chemical: scd30: Prevent potential divide-by-zero errors

[Maxwell Doose]

In scd30_read_raw, the current value of tmp in the
IIO_CHAN_INFO_SAMP_FREQ case is unchecked. Add checking to see if the
value we got was 0 to prevent a divide-by-zero error.

A similar case has also been found in scd30_write_raw(), also in the
IIO_CHAN_INFO_SAMP_FREQ case, where the value of val2 was unchecked.
Add checking for that variable as well and return -EINVAL if it's 0.

Fixes: 64b3d8b1b0f5 ("iio: chemical: scd30: add core driver")
Signed-off-by: Maxwell Doose <m32285159@xxxxxxxxx>
---
 v2:
 - Switch to dev_err_ratelimited() per sashiko.
 - Fix another potential divide-by-zero error per sashiko (see commit
   message).

 drivers/iio/chemical/scd30_core.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/iio/chemical/scd30_core.c b/drivers/iio/chemical/scd30_core.c
index be8c055be184..3851c9334c8b 100644
--- a/drivers/iio/chemical/scd30_core.c
+++ b/drivers/iio/chemical/scd30_core.c
@@ -237,6 +237,16 @@ static int scd30_read_raw(struct iio_dev *indio_dev, struct iio_chan_spec const
 		if (ret)
 			return ret;
 
+		/*
+		 * Value of 0 is unexpected but possible if hardware is failing
+		 * or noise on data bus
+		 */
+		if (!tmp) {
+			dev_err_ratelimited(&indio_dev->dev,
+					    "Invalid measurement interval 0 received\n");
+			return -EIO;
+		}
+
 		*val = 0;
 		*val2 = 1000000000 / tmp;
 		return IIO_VAL_INT_PLUS_NANO;
@@ -261,7 +271,7 @@ static int scd30_write_raw(struct iio_dev *indio_dev, struct iio_chan_spec const
 	guard(mutex)(&state->lock);
 	switch (mask) {
 	case IIO_CHAN_INFO_SAMP_FREQ:
-		if (val)
+		if (val || !val2)
 			return -EINVAL;
 
 		val = 1000000000 / val2;
-- 
2.54.0