Even though I used SuperSU and CWM Recovery to attempt to retain my root control on Android after flashing the stock factory build of 4.2 for my Nexus 7 and Galaxy Nexus I still ended up losing root on both devices which was very not awesome!
Thankfully it seems like there are a few legacy rooting methods for the two devices that still seem to work on 4.2 from 4.1. I’ve got solutions for both devices packed up into .zips for that you can flash using Clockwork Recovery (Sorry, they are not signed so you’ll need a custom recovery). All you’ll need to do is flash these zips on the corresponding device after installing Clockwork Recovery and you’ll boot up retaining root access. Even if you’ve already lost it and booted into the device you can flash these at any time to restore your root access.
Again you do need a custom recovery, but if you’ve already used adb to manually flash you should know how to flash custom recovery. If not I won’t go into details but essentially you grab the recovery image from Clockwork Mod, boot the device into the bootloader, and run ./fastboot flash recovery name-of-recovery-image-from-clockwork.dmg and then ./fastboot reboot and you all set.
Both of these come with SuperSU, not SuperUser app. If you haven’t used SuperSU over SuperUser before give it a shot, I think you’ll find it’s an improvement!
Enjoy Android 4.2! 🙂