Re: leaking path in android binder: set_nice

From: Stephen Smalley
Date: Tue Sep 25 2018 - 13:51:07 EST


On 09/25/2018 01:27 PM, Tong Zhang wrote:
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 binderâs interface to change
a processâs nice value. This path is leaked from being monitored by LSM.
see drivers/android/binder.c:1107 binder_set_nice.

Not sure you want to invoke the LSM hook (or at least the same hook) when binder is performing priority inheritance. There is a difference between a userspace process switching its own priority and the kernel binder driver performing it. IIUC, the can_nice() check is more about honoring RLIMIT_NICE than anything else.