hehe, for me, i start to study linux at 1997. but at that time, nobody teach me and i only act as a normal user. my real touch started from 2000. since i need do kernel programming on that. as u said i only read one part of it.
now i want to devote myself to linux so i begin to know more.
since u do more on security. u had better know the system interface. the interface between user space and kernel, the interface between os and hardware, then read lsm code, i find it is not difficult, u read its code to know why add here, how to finish the access control. how it puts security base... then u will finish u part. and piece by piece, after one or two years, u will know many.