Add symlink and hardlink restrictions that have shown real-world security benefits, along with sysctl knobs to control them. Signed-off-by: Kees Cook <keescook@chromium.org> Signed-off-by: Tim Gardner <tim.gardner@canonical.com> [tyhicks: forward ported from Quantal] Signed-off-by: Tyler Hicks <tyhicks@canonical.com> Signed-off-by: Andy Whitcroft <apw@canonical.com>