TL;DR: We had to prepare an image that bypassed an AppArmor policy that disallowed access to /flag_* path.

Solution: https://github.com/disconnect3d/writeups/tree/master/dsctf2020-apparmor2-task

Original writeup (https://github.com/disconnect3d/writeups/tree/master/dsctf2020-apparmor2-task).