gpiolib: cdev: Fix use after free in lineinfo_changed_notify

jira LE-1907
cve CVE-2024-36899
Rebuild_History Non-Buildable kernel-5.14.0-427.37.1.el9_4
commit-author Zhongqiu Han <quic_zhonhan@quicinc.com>
commit 02f6b0e
Empty-Commit: Cherry-Pick Conflicts during history rebuild.
Will be included in final tarball splat. Ref for failed cherry-pick at:
ciq/ciq_backports/kernel-5.14.0-427.37.1.el9_4/02f6b0e1.failed

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: 51c1064 ("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>
(cherry picked from commit 02f6b0e)
	Signed-off-by: Jonathan Maple <jmaple@ciq.com>

# Conflicts:
#	drivers/gpio/gpiolib-cdev.c

Author: PlaidCat

ciq/ciq_backports/kernel-5.14.0-427.37.1.el9_4/02f6b0e1.failed

@@ -0,0 +1,80 @@
+gpiolib: cdev: Fix use after free in lineinfo_changed_notify
+
+jira LE-1907
+cve CVE-2024-36899
+Rebuild_History Non-Buildable kernel-5.14.0-427.37.1.el9_4
+commit-author Zhongqiu Han <quic_zhonhan@quicinc.com>
+commit 02f6b0e1ec7e0e7d059dddc893645816552039da
+Empty-Commit: Cherry-Pick Conflicts during history rebuild.
+Will be included in final tarball splat. Ref for failed cherry-pick at:
+ciq/ciq_backports/kernel-5.14.0-427.37.1.el9_4/02f6b0e1.failed
+
+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>
+(cherry picked from commit 02f6b0e1ec7e0e7d059dddc893645816552039da)
+	Signed-off-by: Jonathan Maple <jmaple@ciq.com>
+
+# Conflicts:
+#	drivers/gpio/gpiolib-cdev.c
+diff --cc drivers/gpio/gpiolib-cdev.c
+index e81b57db23e3,46a45093d4d0..000000000000
+--- a/drivers/gpio/gpiolib-cdev.c
++++ b/drivers/gpio/gpiolib-cdev.c
+@@@ -2703,9 -2799,11 +2703,15 @@@ static int gpio_chrdev_release(struct i
+  	struct gpio_chardev_data *cdev = file->private_data;
+  	struct gpio_device *gdev = cdev->gdev;
+  
+++<<<<<<< HEAD
+ +	bitmap_free(cdev->watched_lines);
+++=======
++ 	blocking_notifier_chain_unregister(&gdev->device_notifier,
++ 					   &cdev->device_unregistered_nb);
+++>>>>>>> 02f6b0e1ec7e (gpiolib: cdev: Fix use after free in lineinfo_changed_notify)
+  	blocking_notifier_chain_unregister(&gdev->line_state_notifier,
+  					   &cdev->lineinfo_changed_nb);
++ 	bitmap_free(cdev->watched_lines);
+  	gpio_device_put(gdev);
+  	kfree(cdev);
+  
+* Unmerged path drivers/gpio/gpiolib-cdev.c