### TL;DR
Leak the source code via path traversal, then patch the beginning of a binary to
```
#!/bin/busybox sh
sh
```
to confuse `minijail0` to assume the interpreter is dynamically linked (when it is in fact statically linked), making its `LD_PRELOAD` trick useless.

Original writeup (https://blog.pspaul.de/posts/hacklu-ctf-2018-petite-prison/).