Fun task, trolling 11/10.
I solved it after CTF by reading /etc/issue to identify distro and glibc version, and then /proc/self/syscall to get glibc load address.
Not sure how to solve this by reading /proc/self/maps as the flag suggests, since I can read only the first line, and that would give me executable load address, which is not so useful.

Not sure who "Joker's" is trying to fool with their fake writeup, so I'll add a real one.