5.5 - CVE-2022-49315

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

drivers: staging: rtl8192e: Fix deadlock in rtllib_beacons_stop()

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

(Thread 1) | (Thread 2)
| rtllib_send_beacon() rtllib_beacons_stop() | mod_timer()
spin_lock_irqsave() //(1) | (wait a time)
... | rtllib_send_beacon_cb()
del_timer_sync() | spin_lock_irqsave() //(2)
(wait timer to stop) | ...

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

This patch extracts del_timer_sync() from the protection of spin_lock_irqsave(), which could let timer handler to obtain the needed lock.