sched: Don't report SCHED_FLAG_SUGOV in sched_getattr()

SCHED_FLAG_SUGOV is supposed to be a kernel-only flag that userspace
cannot interact with. However, sched_getattr() currently reports it
in sched_flags if called on a sugov worker even though it is not
actually defined in a UAPI header. To avoid this, make sure to
clean-up the sched_flags field in sched_getattr() before returning to
userspace.

Signed-off-by: Quentin Perret <qperret@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210727101103.2729607-3-qperret@google.com

kernel/sched/core.c

@@ -7530,6 +7530,7 @@ SYSCALL_DEFINE4(sched_getattr, pid_t, pid, struct sched_attr __user *, uattr,
 		kattr.sched_priority = p->rt_priority;
 	else
 		kattr.sched_nice = task_nice(p);
+	kattr.sched_flags &= SCHED_FLAG_ALL;
 
 #ifdef CONFIG_UCLAMP_TASK
 	/*