In the Linux kernel, the following vulnerability has been resolved:

serial: core: Clearing the circular buffer before NULLifying it

The circular buffer is NULLified in uart_tty_port_shutdown()
under the spin lock. However, the PM or other timer based callbacks
may still trigger after this event without knowning that buffer pointer
is not valid. Since the serial code is a bit inconsistent in checking
the buffer state (some rely on the head-tail positions, some on the
buffer pointer), it's better to have both aligned, i.e. buffer pointer
to be NULL and head-tail possitions to be the same, meaning it's empty.
This will prevent asynchronous calls to dereference NULL pointer as
reported recently in 8250 case:

  BUG: kernel NULL pointer dereference, address: 00000cf5
  Workqueue: pm pm_runtime_work
  EIP: serial8250_tx_chars (drivers/tty/serial/8250/8250_port.c:1809)
  ...
  ? serial8250_tx_chars (drivers/tty/serial/8250/8250_port.c:1809)
  __start_tx (drivers/tty/serial/8250/8250_port.c:1551)
  serial8250_start_tx (drivers/tty/serial/8250/8250_port.c:1654)
  serial_port_runtime_suspend (include/linux/serial_core.h:667 drivers/tty/serial/serial_port.c:63)
  __rpm_callback (drivers/base/power/runtime.c:393)
  ? serial_port_remove (drivers/tty/serial/serial_port.c:50)
  rpm_suspend (drivers/base/power/runtime.c:447)

The proposed change will prevent ->start_tx() to be called during
suspend on shut down port.

References:
http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2024-26998
https://www.cve.org/CVERecord?id=CVE-2024-26998
https://git.kernel.org/stable/c/7ae7104d54342433a3a73975f6569beefdd86350
https://git.kernel.org/stable/c/9cf7ea2eeb745213dc2a04103e426b960e807940
https://git.kernel.org/stable/c/bb1118905e875c111d7ccef9aee86ac5e4e7f985
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2024/CVE-2024-26998.mbox
https://bugzilla.redhat.com/show_bug.cgi?id=2278303