It turns out the dirtycow exploit is a complex thing with many possible implementations:

https://github.com/dirtycow/dirtycow.github.io/wiki/PoCs

dirtycow-mem.c
I tried them all out and was excited by the supposedly "memory-only" PoC but realized it still needs to do modifications to libc.so in order to work. That's way too risky and offers no benefits to my original implementation - imagine having bricked half of my neighbors' tablets? I would have to take the stairs instead of the elevator just to avoid meeting the angry mob :)

0xdeadbeef/VIKIROOT

vDSO? Never heard of it! It turns out it's a Linux execution optimization feature that features a virtual linux-vdso.so that dirtycow can overwrite (and can't do any permanent damage to) but on the specific x86 Linux kernel build my tablet uses it does not expose enough stuff to work :( :( I learned some x86 assembly and managed to get it to reboot my tablet on command, but no filesystem calls worked and though it had great potential to safely read a read-protected file, it turned out it didn't want to.