CVE-2024-36899

In the Linux kernel, the following vulnerability has been resolved:
gpiolib: cdev: Fix use after free in lineinfo_changed_notify 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.