Yesterday, along with announcing the Galaxy Note 3, Samsung also mentioned that it has stepped up the level of security on its devices and will be providing enterprise level security via KNOX to even the general consumers out there. Soon after, two new firmwares for the Galaxy S4 (I9505) was released with SELinux enabled and set to restrictive.
The above changes itself renders any existing way of rooting the Galaxy S4 useless. The new ROMs also include a new bootloader, which contain a new warranty status check inside it. Once the user has upgraded to these ROMs, it is pretty much not possible to downgrade to an older version of the bootloader. The new warranty status check is also incompatible with Mobile ODIN or Triangle away at the moment.
Samsung is making it tougher and complicated to gain root access on their devices, and all the above changes are the side-effects of the company implementing KNOX to step-up the security levels on its devices.
Thankfully, Chainfire has managed to gain root access on these new firmware, and has already updated SuperSU on the Play Store. If you are already running the GG or H8 firmware on your Galaxy S4, and end up rooting it, keep in mind that the system will constantly notify you with a pop-up that your system has been compromised. You will need to follow the instructions mentioned here to stop the annoying pop-up.
The latest version of SuperSU contains other changes as well including updated binaries, OTA survival issues on Android 4.3 and other minor bug fixes.