leaking path in android binder: set_nice

[Tong Zhang]

Kernel Version: 4.18.5

Problem Description:

When setting nice value, it is checked by LSM function security_task_setnice().
see kernel/sched/core.c:3972 SYSCALL_DEFINE1(nice, int, increment)

We discovered a leaking path in android binder which allows using binder’s interface to change 
a process’s nice value. This path is leaked from being monitored by LSM.
see drivers/android/binder.c:1107 binder_set_nice.

- Tong