[PATCH v3] iio: adc: stm32-adc: fix possible division by zero in processed channel

[Fabrice Gasnier <fabrice.gasnier@foss.st.com>]

In case the conversion has failed or returned zero, processing *val
can lead to a division by zero. Need to check for errors, or converted
value is zero, before processing the data. In case the converted value
is zero, e.g. the Vrefint channel, this should be considered as invalid
in all cases.

Fixes: 0e346b2cfa85 ("iio: adc: stm32-adc: add vrefint calibration support")
Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://lore.kernel.org/all/20260911161555.244F31F000FF@smtp.kernel.org/
Cc: stable@vger.kernel.org
Signed-off-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com>
---
Changes in v3:
- New suggestion from Andy, to move lock release earlier, then return
  when needed. Drop temporary variable.
- Link to v2: https://patch.msgid.link/20260916-adc-fix-div0-v2-1-f702d3ed782c@foss.st.com

Changes in v2:
- Review comments from Andy:
-- Correct commit message: single paragraph
-- Use a temporary variable instead of *val to improve readability
-- Drop ternary operation and use simpler conditional checks
- Link to v1: https://patch.msgid.link/20260915-adc-fix-div0-v1-1-7daed9e52f2f@foss.st.com
---
 drivers/iio/adc/stm32-adc.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/iio/adc/stm32-adc.c b/drivers/iio/adc/stm32-adc.c
index 5c6c06b269be..cac9b18770a5 100644
--- a/drivers/iio/adc/stm32-adc.c
+++ b/drivers/iio/adc/stm32-adc.c
@@ -1608,11 +1608,16 @@ static int stm32_adc_read_raw(struct iio_dev *indio_dev,
 			ret = stm32_adc_single_conv(indio_dev, chan, val);
 		else
 			ret = -EINVAL;
+		iio_device_release_direct(indio_dev);
+		if (ret < 0)
+			return ret;
 
-		if (mask == IIO_CHAN_INFO_PROCESSED)
+		if (mask == IIO_CHAN_INFO_PROCESSED) {
+			if (*val == 0)
+				return -EINVAL;
 			*val = STM32_ADC_VREFINT_VOLTAGE * adc->vrefint.vrefint_cal / *val;
+		}
 
-		iio_device_release_direct(indio_dev);
 		return ret;
 
 	case IIO_CHAN_INFO_SCALE:

---
base-commit: 8d3ae59288f1e7d58d76558a6ee96d533bc5019f
change-id: 20260915-adc-fix-div0-ae38365abfeb

Best regards,
--  
Fabrice Gasnier <fabrice.gasnier@foss.st.com>