linux-kernel - [PATCH] gpiolib: Fix potential NULL pointer dereference in gpiod_get

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Message-ID: <20241003131351.472015-1-prabhakar.mahadev-lad.rj@bp.renesas.com>
Date: Thu,  3 Oct 2024 14:13:51 +0100
From: Prabhakar <prabhakar.csengg@...il.com>
To: Linus Walleij <linus.walleij@...aro.org>,
	Bartosz Golaszewski <brgl@...ev.pl>,
	Geert Uytterhoeven <geert+renesas@...der.be>
Cc: linux-gpio@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-renesas-soc@...r.kernel.org,
	Prabhakar <prabhakar.csengg@...il.com>,
	Biju Das <biju.das.jz@...renesas.com>,
	Fabrizio Castro <fabrizio.castro.jz@...esas.com>,
	Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
Subject: [PATCH] gpiolib: Fix potential NULL pointer dereference in gpiod_get_label()

From: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>

In `gpiod_get_label()`, it is possible that `srcu_dereference_check()` may
return a NULL pointer, leading to a scenario where `label->str` is accessed
without verifying if `label` itself is NULL.

This patch adds a proper NULL check for `label` before accessing
`label->str`. The check for `label->str != NULL` is removed because
`label->str` can never be NULL if `label` is not NULL.

This fixes the issue where the label name was being printed as `(efault)`
when dumping the sysfs GPIO file when `label == NULL`.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
---
Output before this patch:
root@...rc-rzg2l:~# cat /sys/kernel/debug/gpio | grep P2_1
 gpio-529 (P2_1                |(efault)            ) in  hi IRQ

Output after this patch:
root@...rc-rzg2l:~# cat /sys/kernel/debug/gpio | grep P2_1
 gpio-529 (P2_1                |interrupt           ) in  hi IRQ
---
 drivers/gpio/gpiolib.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index c6afbf434366..d5952ab7752c 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -114,12 +114,12 @@ const char *gpiod_get_label(struct gpio_desc *desc)
 				srcu_read_lock_held(&desc->gdev->desc_srcu));
 
 	if (test_bit(FLAG_USED_AS_IRQ, &flags))
-		return label->str ?: "interrupt";
+		return label ? label->str : "interrupt";
 
 	if (!test_bit(FLAG_REQUESTED, &flags))
 		return NULL;
 
-	return label->str;
+	return label ? label->str : NULL;
 }
 
 static void desc_free_label(struct rcu_head *rh)
-- 
2.43.0