Should succeed if ran as root, should fail if run as non-root user
This is a demo program inspired by Jacob Sorber's video.
The method to write to null is provided in a comment by valverde.
The short of valverde's comment (supported by this program) is that you can write to a null pointer by
forcing mmap to not take the supplied address as a hint using the flag MAP_FIXED and running the program as root.
Otherwise, the write should fail for non-root users and the program follows the value at /proc/sys/vm/mmap_min_addr.
This should either cause mmap to map a different address (without MAP_FIXED), or return a permission error (with MAP_FIXED)
It would be possible to change the value of mmap_min_addr for non-root users to be able to do so, but this is a bad idea.
To learn why (and why mmap_min_addr exists), read up on Null Pointer Dereference (NPD) attacks.
Note that mmap maps to virutal memory and not physical memory.