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.

References

• https://nvd.nist.gov/vuln/detail/CVE-2022-49304
• https://git.kernel.org/stable/c/0976808d0d171ec837d4bd3e9f4ad4a00ab703b8
• https://git.kernel.org/stable/c/09a5958a2452ad22d0cb638711ef34ea1863a829
• https://git.kernel.org/stable/c/2cbfc38df580bff5b2fe19f21c1a7520efcc4b3b
• https://git.kernel.org/stable/c/34d91e555e5582cffdbcbb75517bc9217866823e
• https://git.kernel.org/stable/c/553213432ef0c295becdc08c0207d2094468f673
• https://git.kernel.org/stable/c/62b2caef400c1738b6d22f636c628d9f85cd4c4c
• https://git.kernel.org/stable/c/6e2273eefab54a521d9c59efb6e1114e742bdf41
• https://git.kernel.org/stable/c/85e20f8bd31a46d8c60103d0274a8ebe8f47f2b2
• https://git.kernel.org/stable/c/920f0ae7a129ffee98a106e3bbdfd61a2a59e939