CVE-2021-47439

In the Linux kernel, the following vulnerability has been resolved: net:
dsa: microchip: Added the condition for scheduling ksz_mib_read_work When
the ksz module is installed and removed using rmmod, kernel crashes with
null pointer dereferrence error. During rmmod, ksz_switch_remove function
tries to cancel the mib_read_workqueue using cancel_delayed_work_sync
routine and unregister switch from dsa. During dsa_unregister_switch it
calls ksz_mac_link_down, which in turn reschedules the workqueue since
mib_interval is non-zero. Due to which queue executed after mib_interval
and it tries to access dp->slave. But the slave is unregistered in the
ksz_switch_remove function. Hence kernel crashes. To avoid this crash,
before canceling the workqueue, resetted the mib_interval to 0. v1 -> v2:
-Removed the if condition in ksz_mib_read_work