BugLink: http://bugs.launchpad.net/bugs/1566221

custom_method effectively allows arbitrary access to system memory, making
it possible for an attacker to circumvent restrictions on module loading.
Disable it if any such restrictions have been enabled.
Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>