CVE-2024-26998

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.