[PATCH v2] staging: iio: adc: ad7816: Protect sysfs attributes with mutex

[Abdelnasser Hussein <abdelnasserhussein11@gmail.com>]

The sysfs store functions (ad7816_store_mode and ad7816_store_channel)
modify the device state and toggle GPIO pins. If accessed concurrently
by userspace during an ongoing SPI transfer, this could corrupt the
SPI transaction.

Add the existing chip->lock guard to these functions to serialize
access and prevent race conditions.

Fixes: 7924425db04a ("staging: iio: adc: new driver for AD7816 devices")
Suggested-by: Joshua Crofts <joshua.crofts1@gmail.com>
Reviewed-by: Joshua Crofts <joshua.crofts1@gmail.com>
Signed-off-by: Abdelnasser Hussein <abdelnasserhussein11@gmail.com>
---
Changes in v2:
- Added a blank line after guard(mutex) statements as requested by Joshua.
- Added Fixes tag as requested by Dan.
- Collected Reviewed-by tag from Joshua.

 drivers/staging/iio/adc/ad7816.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/staging/iio/adc/ad7816.c b/drivers/staging/iio/adc/ad7816.c
index f76f0215119a..2a15d7598abb 100644
--- a/drivers/staging/iio/adc/ad7816.c
+++ b/drivers/staging/iio/adc/ad7816.c
@@ -143,6 +143,8 @@ static ssize_t ad7816_store_mode(struct device *dev,
 	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
 	struct ad7816_chip_info *chip = iio_priv(indio_dev);
 
+	guard(mutex)(&chip->lock);
+
 	if (strcmp(buf, "full") == 0) {
 		gpiod_set_value(chip->rdwr_pin, 1);
 		chip->mode = AD7816_FULL;
@@ -207,6 +209,8 @@ static ssize_t ad7816_store_channel(struct device *dev,
 		return -EINVAL;
 	}
 
+	guard(mutex)(&chip->lock);
+
 	chip->channel_id = data;
 
 	return len;
-- 
2.54.0