I see. Wouldn't it make sense to have the more recent "longterm" kernel available for install as an option? I don't understand why there is mentioning of backporting security fixes when you could just use one of those kernels and have the patches backported. Is there a reason to keep using 4.12? I just checked and F2FS security fixes seem to be backported to Linux 4.9, 4.14 and 4.19.