linux-luminarium: add hidden disk doomsday test

Author: zardus

challenges/linux-luminarium/destruction/disk-doomsday-test/DESCRIPTION.md

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+The available space in `/home/hacker` in this container is deliberately limited.
+In this level you will clog up `/home/hacker` with so much junk that even a tiny 1 megabyte file can't be created.
+When this happens, your workspace becomes unusable.
+We'll practice inducing this in this challenge, and then expand on it a bit later.
+
+How to fill the disk?
+There are so many ways.
+Here, we'll teach you the `yes` command!
+
+```
+hacker@dojo:~$ yes | head
+y
+y
+y
+y
+y
+y
+y
+y
+y
+y
+hacker@dojo:~$
+```
+
+The `yes` outputs `y` over and over forever.
+The typical usage is to automate confirmation prompts ("Are you sure you want to delete this file?") using piping, but we'll use it here to make a massive file full of "y" lines.
+Just redirect `yes` to a file in your home directory, and you'll fill your disk!
+
+This challenge forces you to fill the disk and then clean up.
+The process:
+
+1. Fill your disk.
+2. Run `/challenge/check`. It will attempt to create a 1 megabyte temporary file. If that fails, you pass the first stage and the checker will ask you to free the space.
+3. Delete the file you made (with `rm`) to clear up the space.
+4. Run `/challenge/check` a second time.  If it can now create the temporary file (i.e., you successfully cleaned up your home directory), you’ll receive the flag.
+
+----
+**Why two stages?**
+For local runs, this challenge gives you a temporary, size-limited home directory for the exercise.
+On pwn.college, your home directory persists across challenge instances.
+If we let you keep it full, your pwn.college will stop working.
+This is _by far_ the most common cause of weird issues on pwn.college!
+
+**HELP IT BROKE!**
+If you fill the disk and don't clean it up afterwards, you'll need to `ssh` in to fix things (by removing that file).
+This is a bit tricky, but we describe how to do it under "Connecting over SSH" in the [Getting Started](/welcome/welcome) module.

challenges/linux-luminarium/destruction/disk-doomsday-test/challenge.yml

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+privileged: true

challenges/linux-luminarium/destruction/disk-doomsday-test/challenge/.init

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+#!/bin/bash
+set -e
+
+# Bound the disposable pwnshop home without hiding a deployed persistent home.
+if [ "$(findmnt -n -o TARGET -T /home/hacker)" = "/" ]; then
+    mount -t tmpfs -o size=64M,mode=0755,nosuid,nodev tmpfs /home/hacker
+    chown hacker:hacker /home/hacker
+fi

challenges/linux-luminarium/destruction/disk-doomsday-test/challenge/Dockerfile.j2

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+{% include "../../../common/Dockerfile.j2" %}

challenges/linux-luminarium/destruction/disk-doomsday-test/challenge/check

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+#!/usr/bin/exec-suid -- /usr/bin/python3 -I
+
+import errno
+import os
+import sys
+import tempfile
+
+MARKER = "/run/disk_doomsday_phase1"
+TEST_SIZE = 1 * 1024 * 1024
+
+
+def try_create():
+    fd = None
+    path = None
+    try:
+        fd, path = tempfile.mkstemp(prefix=".space_test.", dir="/home/hacker")
+        os.posix_fallocate(fd, 0, TEST_SIZE)
+    except OSError as error:
+        if error.errno in (errno.EDQUOT, errno.ENOSPC):
+            return False
+        print("Unexpected failure creating temporary file.")
+        sys.exit(1)
+    finally:
+        if fd is not None:
+            os.close(fd)
+        if path is not None:
+            try:
+                os.remove(path)
+            except FileNotFoundError:
+                pass
+    return True
+
+
+can_create = try_create()
+
+if not os.path.exists(MARKER):
+    if can_create:
+        print(
+            "Plenty of space remains. Fill up /home/hacker until a 1 MB file cannot be created "
+            "and run this checker again."
+        )
+    else:
+        open(MARKER, "w").close()
+        print(
+            "Well done, you clogged the disk. Now free that space (remove the file you created) "
+            "and run /challenge/check again to prove you cleaned up!"
+        )
+elif not can_create:
+    print("Still no space left. Clean up more and try again!")
+else:
+    print("Disk space restored. Here is your flag:")
+    print(open("/flag").read().strip())

challenges/linux-luminarium/destruction/disk-doomsday-test/tests_private/test_solve.sh

@@ -7,6 +7,12 @@ resources:
 - type: challenge
   id: disk-doomsday
   name: Disk-Space Doomsday
+- type: challenge
+  id: disk-doomsday-test
+  name: Disk-Space Doomsday (Test)
+  required: false
+  visibility:
+    start: "2099-01-01T00:00:00+00:00"
 - type: challenge
   id: rm-rf-root
   name: rm -rf /