[PATCH] iio: adc: at91_adc: fix NULL pointer deref in trigger removal

[Abdelnasser Hussein <abdelnasserhussein11@gmail.com>]

If 'atmel,adc-use-external-triggers' is not set in the device tree,
at91_adc_trigger_init() leaves the external trigger slots in st->trig
as NULL. at91_adc_trigger_remove(), also used by the probe error path,
then calls iio_trigger_unregister() and iio_trigger_free() on them
unconditionally, causing a NULL pointer dereference.

Skip NULL triggers when unregistering and freeing.

Fixes: 0e589d5fb317 ("ARM: AT91: IIO: Add AT91 ADC driver.")
Signed-off-by: Abdelnasser Hussein <abdelnasserhussein11@gmail.com>
---
 drivers/iio/adc/at91_adc.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/iio/adc/at91_adc.c b/drivers/iio/adc/at91_adc.c
index 0ac74ad92fca..c7fc06214c05 100644
--- a/drivers/iio/adc/at91_adc.c
+++ b/drivers/iio/adc/at91_adc.c
@@ -660,6 +660,8 @@ static int at91_adc_trigger_init(struct iio_dev *idev)
 
 error_trigger:
 	for (i--; i >= 0; i--) {
+		if (!st->trig[i])
+			continue;
 		iio_trigger_unregister(st->trig[i]);
 		iio_trigger_free(st->trig[i]);
 	}
@@ -673,6 +675,8 @@ static void at91_adc_trigger_remove(struct iio_dev *idev)
 	int i;
 
 	for (i = 0; i < st->caps->trigger_number; i++) {
+		if (!st->trig[i])
+			continue;
 		iio_trigger_unregister(st->trig[i]);
 		iio_trigger_free(st->trig[i]);
 	}
-- 
2.56.0