[PATCH] gpio: cdev: fix a crash on line-request release

[Bartosz Golaszewski <brgl@bgdev.pl>]

When a GPIO device is forcefully unregistered, we are left with an
inactive object. If user-space kept an open file descriptor to a line
request associated with such a structure, upon closing it, we'll see the
kernel crash due to freeing unexistent GPIO descriptors.

Fix it by checking if chip is still alive before calling gpiod_free() in
release callbacks for both v2 and v1 ABI.

Fixes: 3c0d9c635ae2 ("gpiolib: cdev: support GPIO_V2_GET_LINE_IOCTL and GPIO_V2_LINE_GET_VALUES_IOCTL")
Reported-by: Kent Gibson <warthog618@gmail.com>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>
---
 drivers/gpio/gpiolib-cdev.c | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
index 0a33971c964c..6830f668a1b0 100644
--- a/drivers/gpio/gpiolib-cdev.c
+++ b/drivers/gpio/gpiolib-cdev.c
@@ -315,13 +315,19 @@ static long linehandle_ioctl_compat(struct file *file, unsigned int cmd,
 
 static void linehandle_free(struct linehandle_state *lh)
 {
+	struct gpio_device *gdev = lh->gdev;
 	int i;
 
-	for (i = 0; i < lh->num_descs; i++)
-		if (lh->descs[i])
-			gpiod_free(lh->descs[i]);
+	for (i = 0; i < lh->num_descs; i++) {
+		if (lh->descs[i]) {
+			down_write(&gdev->sem);
+			if (gdev->chip)
+				gpiod_free(lh->descs[i]);
+			up_write(&gdev->sem);
+		}
+	}
 	kfree(lh->label);
-	gpio_device_put(lh->gdev);
+	gpio_device_put(gdev);
 	kfree(lh);
 }
 
@@ -1565,17 +1571,21 @@ static ssize_t linereq_read(struct file *file, char __user *buf,
 
 static void linereq_free(struct linereq *lr)
 {
+	struct gpio_device *gdev = lr->gdev;
 	unsigned int i;
 
 	for (i = 0; i < lr->num_lines; i++) {
 		if (lr->lines[i].desc) {
 			edge_detector_stop(&lr->lines[i]);
-			gpiod_free(lr->lines[i].desc);
+			down_write(&gdev->sem);
+			if (gdev->chip)
+				gpiod_free(lr->lines[i].desc);
+			up_write(&gdev->sem);
 		}
 	}
 	kfifo_free(&lr->events);
 	kfree(lr->label);
-	gpio_device_put(lr->gdev);
+	gpio_device_put(gdev);
 	kfree(lr);
 }
 
-- 
2.39.2