gpio: cdev: check for NULL labels when sanitizing them for irqs

We need to take into account that a line's consumer label may be NULL
and not try to kstrdup() it in that case but rather pass the NULL
pointer up the stack to the interrupt request function.

To that end: let make_irq_label() return NULL as a valid return value
and use ERR_PTR() instead to signal an allocation failure to callers.

Cc: stable@vger.kernel.org
Fixes: b3449087 ("gpio: cdev: sanitize the label before requesting the interrupt")
Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
Closes: https://lore.kernel.org/lkml/20240402093534.212283-1-naresh.kamboju@linaro.org/Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Tested-by: Anders Roxell <anders.roxell@linaro.org>

drivers/gpio/gpiolib-cdev.c

@@ -1085,7 +1085,16 @@ static u32 gpio_v2_line_config_debounce_period(struct gpio_v2_line_config *lc,
 
 static inline char *make_irq_label(const char *orig)
 {
-	return kstrdup_and_replace(orig, '/', ':', GFP_KERNEL);
+	char *new;
+
+	if (!orig)
+		return NULL;
+
+	new = kstrdup_and_replace(orig, '/', ':', GFP_KERNEL);
+	if (!new)
+		return ERR_PTR(-ENOMEM);
+
+	return new;
 }
 
 static inline void free_irq_label(const char *label)
@@ -1158,8 +1167,8 @@ static int edge_detector_setup(struct line *line,
 	irqflags |= IRQF_ONESHOT;
 
 	label = make_irq_label(line->req->label);
-	if (!label)
-		return -ENOMEM;
+	if (IS_ERR(label))
+		return PTR_ERR(label);
 
 	/* Request a thread to read the events */
 	ret = request_threaded_irq(irq, edge_irq_handler, edge_irq_thread,
@@ -2217,8 +2226,8 @@ static int lineevent_create(struct gpio_device *gdev, void __user *ip)
 		goto out_free_le;
 
 	label = make_irq_label(le->label);
-	if (!label) {
-		ret = -ENOMEM;
+	if (IS_ERR(label)) {
+		ret = PTR_ERR(label);
 		goto out_free_le;
 	}