BACKPORT: seccomp: create internal mode-setting function

In preparation for having other callers of the seccomp mode setting
logic, split the prctl entry point away from the core logic that performs
seccomp mode setting.

Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Andy Lutomirski <luto@amacapital.net>

Bug: 28020023
Patchset: seccomp

(cherry picked from kernel/msm commit 82e69a633c6f19551fb75fcea5a998d57bbddde7)
Signed-off-by: Kees Cook <keescook@google.com>
Change-Id: I40ac488c5bfa57ce8e4deee4d0f7e6248dcb2d30
1 file changed