linux-kernel - [PATCH] gpio: cdev: fix a NULL-pointer dereference with DEBUG enabled

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Date: Fri, 16 Feb 2024 11:59:30 +0100
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Bartosz Golaszewski <brgl@...ev.pl>,
	Kent Gibson <warthog618@...il.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	"Paul E . McKenney" <paulmck@...nel.org>
Cc: linux-gpio@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>
Subject: [PATCH] gpio: cdev: fix a NULL-pointer dereference with DEBUG enabled

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

We are actually passing the gc pointer to chip_dbg() so we have to
srcu_dereference() it.

Fixes: 8574b5b47610 ("gpio: cdev: use correct pointer accessors with SRCU")
Reported-by: Marek Szyprowski <m.szyprowski@...sung.com>
Closes: https://lore.kernel.org/lkml/179caa10-5f86-4707-8bb0-fe1b316326d6@samsung.com/
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
---
 drivers/gpio/gpiolib-cdev.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
index 85037fa4925e..f384fa278764 100644
--- a/drivers/gpio/gpiolib-cdev.c
+++ b/drivers/gpio/gpiolib-cdev.c
@@ -2795,8 +2795,8 @@ int gpiolib_cdev_register(struct gpio_device *gdev, dev_t devt)
 		return ret;
 
 	guard(srcu)(&gdev->srcu);
-
-	if (!rcu_access_pointer(gdev->chip))
+	gc = srcu_dereference(gdev->chip, &gdev->srcu);
+	if (!gc)
 		return -ENODEV;
 
 	chip_dbg(gc, "added GPIO chardev (%d:%d)\n", MAJOR(devt), gdev->id);
-- 
2.40.1