CVE-2022-49304: Improper Locking

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

drivers: tty: serial: Fix deadlock in sa1100_set_termios()

There is a deadlock in sa1100_set_termios(), which is shown below:

(Thread 1) | (Thread 2) | sa1100_enable_ms() sa1100_set_termios() | mod_timer() spin_lock_irqsave() //(1) | (wait a time) ... | sa1100_timeout() del_timer_sync() | spin_lock_irqsave() //(2) (wait timer to stop) | ...

We hold sport->port.lock in position (1) of thread 1 and use del_timer_sync() to wait timer to stop, but timer handler also need sport->port.lock in position (2) of thread 2. As a result, sa1100_set_termios() will block forever.

This patch moves del_timer_sync() before spin_lock_irqsave() in order to prevent the deadlock.