[PATCH] gpio: shared: fix a NULL-pointer dereference

[Bartosz Golaszewski <brgl@bgdev.pl>]

From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

The fact that CONFIG_OF is enabled does not mean that the device tree is
populated and that of_root points to a valid device node. Check if it's
NULL before trying to traverse the tree.

Fixes: a060b8c511ab ("gpiolib: implement low-level, shared GPIO support")
Reported-by: Mark Brown <broonie@kernel.org>
Closes: https://lore.kernel.org/all/dbe20642-9662-40af-a593-c1263baea73b@sirena.org.uk/
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
---
 drivers/gpio/gpiolib-shared.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/gpio/gpiolib-shared.c b/drivers/gpio/gpiolib-shared.c
index c22eaf05eef23..4ce574a21850b 100644
--- a/drivers/gpio/gpiolib-shared.c
+++ b/drivers/gpio/gpiolib-shared.c
@@ -205,7 +205,10 @@ static int gpio_shared_of_traverse(struct device_node *curr)
 
 static int gpio_shared_of_scan(void)
 {
-	return gpio_shared_of_traverse(of_root);
+	if (of_root)
+		return gpio_shared_of_traverse(of_root);
+
+	return 0;
 }
 #else
 static int gpio_shared_of_scan(void)
-- 
2.51.0