[PATCH v2 1/5] gpiolib: cdev: add gpio_device locking wrapper around gpio_ioctl()

[Kent Gibson]

While the GPIO cdev gpio_ioctl() call is in progress, the kernel can
call gpiochip_remove() which will set gdev->chip to NULL, after which
any subsequent access will cause a crash.

gpio_ioctl() was overlooked by the previous fix to protect syscalls
(bdbbae241a04), so add protection for that.

Fixes: bdbbae241a04 ("gpiolib: protect the GPIO device against being dropped while in use by user-space")
Fixes: d7c51b47ac11 ("gpio: userspace ABI for reading/writing GPIO lines")
Fixes: 3c0d9c635ae2 ("gpiolib: cdev: support GPIO_V2_GET_LINE_IOCTL and GPIO_V2_LINE_GET_VALUES_IOCTL")
Fixes: aad955842d1c ("gpiolib: cdev: support GPIO_V2_GET_LINEINFO_IOCTL and GPIO_V2_GET_LINEINFO_WATCH_IOCTL")
Signed-off-by: Kent Gibson <warthog618@xxxxxxxxx>
---
 drivers/gpio/gpiolib-cdev.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
index 744734405912..9155c54acc1e 100644
--- a/drivers/gpio/gpiolib-cdev.c
+++ b/drivers/gpio/gpiolib-cdev.c
@@ -2598,10 +2598,7 @@ static int lineinfo_unwatch(struct gpio_chardev_data *cdev, void __user *ip)
 	return 0;
 }
 
-/*
- * gpio_ioctl() - ioctl handler for the GPIO chardev
- */
-static long gpio_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
+static long gpio_ioctl_unlocked(struct file *file, unsigned int cmd, unsigned long arg)
 {
 	struct gpio_chardev_data *cdev = file->private_data;
 	struct gpio_device *gdev = cdev->gdev;
@@ -2638,6 +2635,17 @@ static long gpio_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 	}
 }
 
+/*
+ * gpio_ioctl() - ioctl handler for the GPIO chardev
+ */
+static long gpio_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
+{
+	struct gpio_chardev_data *cdev = file->private_data;
+
+	return call_ioctl_locked(file, cmd, arg, cdev->gdev,
+				 gpio_ioctl_unlocked);
+}
+
 #ifdef CONFIG_COMPAT
 static long gpio_ioctl_compat(struct file *file, unsigned int cmd,
 			      unsigned long arg)
-- 
2.39.2