CVE ID:	CVE-2024-26998
Description:	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.
Test IDs:	None available
Cross References:	Common Vulnerability Exposure (CVE) ID: CVE-2024-26998 https://git.kernel.org/stable/c/7ae7104d54342433a3a73975f6569beefdd86350 https://git.kernel.org/stable/c/7ae7104d54342433a3a73975f6569beefdd86350 https://git.kernel.org/stable/c/9cf7ea2eeb745213dc2a04103e426b960e807940 https://git.kernel.org/stable/c/9cf7ea2eeb745213dc2a04103e426b960e807940 https://git.kernel.org/stable/c/bb1118905e875c111d7ccef9aee86ac5e4e7f985 https://git.kernel.org/stable/c/bb1118905e875c111d7ccef9aee86ac5e4e7f985