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

Vulnerability Description

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://git.kernel.org/stable/c/0976808d0d171ec837d4bd3e9f4ad4a00ab703b8
• https://git.kernel.org/stable/c/85e20f8bd31a46d8c60103d0274a8ebe8f47f2b2
• https://git.kernel.org/stable/c/920f0ae7a129ffee98a106e3bbdfd61a2a59e939
• https://git.kernel.org/stable/c/09a5958a2452ad22d0cb638711ef34ea1863a829
• https://git.kernel.org/stable/c/6e2273eefab54a521d9c59efb6e1114e742bdf41
• https://git.kernel.org/stable/c/2cbfc38df580bff5b2fe19f21c1a7520efcc4b3b
• https://git.kernel.org/stable/c/553213432ef0c295becdc08c0207d2094468f673
• https://git.kernel.org/stable/c/34d91e555e5582cffdbcbb75517bc9217866823e
• https://git.kernel.org/stable/c/62b2caef400c1738b6d22f636c628d9f85cd4c4c