diff mbox series

[v2] gpiolib: cdev: Fix use after free in lineinfo_changed_notify

Message ID 20240505141156.2944912-1-quic_zhonhan@quicinc.com
State New
Headers show
Series [v2] gpiolib: cdev: Fix use after free in lineinfo_changed_notify | expand

Commit Message

Zhongqiu Han May 5, 2024, 2:11 p.m. UTC
The use-after-free issue occurs as follows: when the GPIO chip device file
is being closed by invoking gpio_chrdev_release(), watched_lines is freed
by bitmap_free(), but the unregistration of lineinfo_changed_nb notifier
chain failed due to waiting write rwsem. Additionally, one of the GPIO
chip's lines is also in the release process and holds the notifier chain's
read rwsem. Consequently, a race condition leads to the use-after-free of
watched_lines.

Here is the typical stack when issue happened:

[free]
gpio_chrdev_release()
  --> bitmap_free(cdev->watched_lines)                  <-- freed
  --> blocking_notifier_chain_unregister()
    --> down_write(&nh->rwsem)                          <-- waiting rwsem
          --> __down_write_common()
            --> rwsem_down_write_slowpath()
                  --> schedule_preempt_disabled()
                    --> schedule()

[use]
st54spi_gpio_dev_release()
  --> gpio_free()
    --> gpiod_free()
      --> gpiod_free_commit()
        --> gpiod_line_state_notify()
          --> blocking_notifier_call_chain()
            --> down_read(&nh->rwsem);                  <-- held rwsem
            --> notifier_call_chain()
              --> lineinfo_changed_notify()
                --> test_bit(xxxx, cdev->watched_lines) <-- use after free

The side effect of the use-after-free issue is that a GPIO line event is
being generated for userspace where it shouldn't. However, since the chrdev
is being closed, userspace won't have the chance to read that event anyway.

To fix the issue, call the bitmap_free() function after the unregistration
of lineinfo_changed_nb notifier chain.

Fixes: 51c1064e82e7 ("gpiolib: add new ioctl() for monitoring changes in line info")
Signed-off-by: Zhongqiu Han <quic_zhonhan@quicinc.com>
---
v1 -> v2:
- Drop the excessive stack log from commit message to make it more readable.
- Add a note regarding the side effects of the use-after-free on commit message.
- Link to v1: https://lore.kernel.org/lkml/20240501022612.1787143-1-quic_zhonhan@quicinc.com/

 drivers/gpio/gpiolib-cdev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Bartosz Golaszewski May 9, 2024, 2:33 p.m. UTC | #1
From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>


On Sun, 05 May 2024 22:11:56 +0800, Zhongqiu Han wrote:
> The use-after-free issue occurs as follows: when the GPIO chip device file
> is being closed by invoking gpio_chrdev_release(), watched_lines is freed
> by bitmap_free(), but the unregistration of lineinfo_changed_nb notifier
> chain failed due to waiting write rwsem. Additionally, one of the GPIO
> chip's lines is also in the release process and holds the notifier chain's
> read rwsem. Consequently, a race condition leads to the use-after-free of
> watched_lines.
> 
> [...]

Applied, thanks!

[1/1] gpiolib: cdev: Fix use after free in lineinfo_changed_notify
      commit: 02f6b0e1ec7e0e7d059dddc893645816552039da

Best regards,
diff mbox series

Patch

diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
index d09c7d728365..6b3a43e3ba47 100644
--- a/drivers/gpio/gpiolib-cdev.c
+++ b/drivers/gpio/gpiolib-cdev.c
@@ -2799,11 +2799,11 @@  static int gpio_chrdev_release(struct inode *inode, struct file *file)
 	struct gpio_chardev_data *cdev = file->private_data;
 	struct gpio_device *gdev = cdev->gdev;
 
-	bitmap_free(cdev->watched_lines);
 	blocking_notifier_chain_unregister(&gdev->device_notifier,
 					   &cdev->device_unregistered_nb);
 	blocking_notifier_chain_unregister(&gdev->line_state_notifier,
 					   &cdev->lineinfo_changed_nb);
+	bitmap_free(cdev->watched_lines);
 	gpio_device_put(gdev);
 	kfree(cdev);