[PATCH v2 5/6] gpiolib: cdev: don't leak the IRQ name when the chip is removed

[Adrian Ambrozewicz <aambrozewicz@nvidia.com>]

The character device requests line IRQs with a copy of the consumer
label as the name and frees that copy with the name free_irq() returns.
Since commit ec8b6f55b981 ("gpio: free irqs that are still requested
when the chip is being removed"), gpiochip_remove() may free the IRQ
first and drops the name it gets back. The character device then does
not get it from its own free_irq() call, which since the previous patch
it does not even make, so the copy leaks:

  unreferenced object (size 8):
    comm "gpio-hold"
    backtrace:
      kstrdup
      kstrdup_and_replace
      edge_detector_setup
      linereq_create
      gpio_ioctl

Keep the name with the line, or with the v1 line event, and free it
there whoever freed the IRQ.

Reproduced with gpio-sim and a line requested with edge detection and
a consumer label, the chip being removed while the request is open:
kmemleak reports between 17 and 23 such objects after 30 cycles; with
this change, none after 100.

Fixes: ec8b6f55b981 ("gpio: free irqs that are still requested when the chip is being removed")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Adrian Ambrozewicz <aambrozewicz@nvidia.com>
---
Changes in v2:
- Rebased on the free_line_irq() shape from patch 3, so this only
  changes where the name comes from (Andy).
- kmemleak report cut down (Andy).
- Assisted-by tag.

 drivers/gpio/gpiolib-cdev.c | 23 ++++++++++++++++-------
 1 file changed, 16 insertions(+), 7 deletions(-)

diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
index 6f84aaa95033..788a36475e5d 100644
--- a/drivers/gpio/gpiolib-cdev.c
+++ b/drivers/gpio/gpiolib-cdev.c
@@ -399,6 +399,7 @@ static int linehandle_create(struct gpio_device *gdev, void __user *ip)
  * @desc: the GPIO descriptor for this line.
  * @req: the corresponding line request
  * @irq: the interrupt triggered in response to events on this GPIO
+ * @irq_label: the name @irq was requested with
  * @edflags: the edge flags, GPIO_V2_LINE_FLAG_EDGE_RISING and/or
  * GPIO_V2_LINE_FLAG_EDGE_FALLING, indicating the edge detection applied
  * @timestamp_ns: cache for the timestamp storing it between hardirq and
@@ -422,6 +423,7 @@ struct line {
 	 */
 	struct linereq *req;
 	unsigned int irq;
+	char *irq_label;
 	/*
 	 * The flags for the active edge detector configuration.
 	 *
@@ -601,16 +603,18 @@ static inline void free_irq_label(const char *label)
 /*
  * gpiochip_remove() frees the interrupts still requested on the lines of the
  * chip being removed, so once the chip is going away the IRQ may no longer be
- * ours to free.
+ * ours to free. The label is kept by the caller as free_irq() is then not the
+ * one returning it.
  */
-static void free_line_irq(unsigned int irq, void *dev_id)
+static void free_line_irq(unsigned int irq, void *dev_id, char **label)
 {
-	const char *name = NULL;
+	const char *name = *label;
 
 	if (irq && irq_has_action(irq))
-		name = free_irq(irq, dev_id);
+		free_irq(irq, dev_id);
 
 	free_irq_label(name);
+	*label = NULL;
 }
 
 #ifdef CONFIG_HTE
@@ -936,6 +940,7 @@ static int debounce_setup(struct line *line, unsigned int debounce_period_us)
 				return ret;
 			}
 			line->irq = irq;
+			line->irq_label = label;
 		} else {
 			ret = hte_edge_setup(line, GPIO_V2_LINE_FLAG_EDGE_BOTH);
 			if (ret)
@@ -978,7 +983,7 @@ static u32 gpio_v2_line_config_debounce_period(struct gpio_v2_line_config *lc,
 
 static void edge_detector_stop(struct line *line)
 {
-	free_line_irq(line->irq, line);
+	free_line_irq(line->irq, line, &line->irq_label);
 	line->irq = 0;
 
 #ifdef CONFIG_HTE
@@ -1078,6 +1083,7 @@ static int edge_detector_setup(struct line *line,
 	}
 
 	line->irq = irq;
+	line->irq_label = label;
 	return 0;
 }
 
@@ -1781,6 +1787,7 @@ static int linereq_create(struct gpio_device *gdev, void __user *ip)
  * @desc: the GPIO descriptor held by this event
  * @eflags: the event flags this line was requested with
  * @irq: the interrupt that trigger in response to events on this GPIO
+ * @irq_label: the name @irq was requested with
  * @wait: wait queue that handles blocking reads of events
  * @device_unregistered_nb: notifier block for receiving gdev unregister events
  * @events: KFIFO for the GPIO events
@@ -1794,6 +1801,7 @@ struct lineevent_state {
 	struct gpio_desc *desc;
 	u32 eflags;
 	int irq;
+	char *irq_label;
 	wait_queue_head_t wait;
 	struct notifier_block device_unregistered_nb;
 	DECLARE_KFIFO(events, struct gpioevent_data, 16);
@@ -1829,7 +1837,7 @@ static int lineevent_unregistered_notify(struct notifier_block *nb,
 	struct lineevent_state *le = container_of(nb, struct lineevent_state,
 						  device_unregistered_nb);
 
-	free_line_irq(le->irq, le);
+	free_line_irq(le->irq, le, &le->irq_label);
 	le->irq = 0;
 
 	wake_up_poll(&le->wait, EPOLLIN | EPOLLERR);
@@ -1913,7 +1921,7 @@ static void lineevent_free(struct lineevent_state *le)
 	if (le->device_unregistered_nb.notifier_call)
 		blocking_notifier_chain_unregister(&le->gdev->device_notifier,
 						   &le->device_unregistered_nb);
-	free_line_irq(le->irq, le);
+	free_line_irq(le->irq, le, &le->irq_label);
 	if (le->desc)
 		gpiod_free(le->desc);
 	kfree(le->label);
@@ -2152,6 +2160,7 @@ static int lineevent_create(struct gpio_device *gdev, void __user *ip)
 	}
 
 	le->irq = irq;
+	le->irq_label = label;
 
 	FD_PREPARE(fdf, O_RDONLY | O_CLOEXEC,
 		   anon_inode_getfile("gpio-event", &lineevent_fileops, le,
-- 
2.43.0