[PATCH 6.1] gpiolib: cdev: Fix use after free in lineinfo_changed_notify

[PATCH 6.1] gpiolib: cdev: Fix use after free in lineinfo_changed_notify

[Xiangyu Chen]

From: Zhongqiu Han <quic_zhonhan@quicinc.com>

[ Upstream commit 02f6b0e1ec7e0e7d059dddc893645816552039da ]

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>
Link: https://lore.kernel.org/r/20240505141156.2944912-1-quic_zhonhan@quicinc.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Signed-off-by: Xiangyu Chen <xiangyu.chen@windriver.com>
---
 drivers/gpio/gpiolib-cdev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
index 55f640ef3fee..897d20996a8c 100644
--- a/drivers/gpio/gpiolib-cdev.c
+++ b/drivers/gpio/gpiolib-cdev.c
@@ -2860,9 +2860,9 @@ 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->notifier,
 					   &cdev->lineinfo_changed_nb);
+	bitmap_free(cdev->watched_lines);
 	put_device(&gdev->dev);
 	kfree(cdev);
 
-- 
2.43.0

Re: [PATCH 6.1] gpiolib: cdev: Fix use after free in lineinfo_changed_notify

[Sasha Levin]

[ Sasha's backport helper bot ]

Hi,

The upstream commit SHA1 provided is correct: 02f6b0e1ec7e0e7d059dddc893645816552039da

WARNING: Author mismatch between patch and upstream commit:
Backport author: Xiangyu Chen <xiangyu.chen@eng.windriver.com>
Commit author: Zhongqiu Han <quic_zhonhan@quicinc.com>

Commit in newer trees:

|-----------------|----------------------------------------------|
| 6.11.y          |  Present (exact SHA1)                        |
| 6.6.y           |  Present (different SHA1: 95ca7c90eaf5)      |
| 6.1.y           |  Not found                                   |
|-----------------|----------------------------------------------|

Note: The patch differs from the upstream commit:
---
--- -	2024-11-18 16:31:52.602756021 -0500
+++ /tmp/tmp.fT2zVEHAD2	2024-11-18 16:31:52.593493881 -0500
@@ -1,3 +1,5 @@
+[ Upstream commit 02f6b0e1ec7e0e7d059dddc893645816552039da ]
+
 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
@@ -41,24 +43,26 @@
 Signed-off-by: Zhongqiu Han <quic_zhonhan@quicinc.com>
 Link: https://lore.kernel.org/r/20240505141156.2944912-1-quic_zhonhan@quicinc.com
 Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
+Signed-off-by: Xiangyu Chen <xiangyu.chen@windriver.com>
 ---
  drivers/gpio/gpiolib-cdev.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)
 
 diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
-index fea149ae77741..46a45093d4d0d 100644
+index 55f640ef3fee..897d20996a8c 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)
+@@ -2860,9 +2860,9 @@ 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,
+ 	blocking_notifier_chain_unregister(&gdev->notifier,
  					   &cdev->lineinfo_changed_nb);
 +	bitmap_free(cdev->watched_lines);
- 	gpio_device_put(gdev);
+ 	put_device(&gdev->dev);
  	kfree(cdev);
  
+-- 
+2.43.0
+
---

Results of testing on various branches:

| Branch                    | Patch Apply | Build Test |
|---------------------------|-------------|------------|
| stable/linux-6.1.y        |  Success    |  Success   |