Challenge 1: Overbooked

ChallengesChallenge 1 of 590 minutesChallenge

Overbooked

The booking desk handles freight. You book a consignment as a number of crates, each carrying sixteen bytes of manifest, and then stow the crates one at a time. The desk will not release a consignment that customs has not cleared, and nothing you are given clears one.

Your goal is to get the release note printed.

Hands-on lab

There are no milestones on this page and no hints. Read How These Challenges Work first.

Finish Bug Classes and Primitives and The Heap first.

Work inside the Ubuntu Desktop 24.04.4 LTS x86-64 course VM with GCC 13.x, GNU binutils 2.42 and GDB 15.x. Address randomization can stay at its default.

Get the files

Download overbooked-v1.0.0.tar into ~/underdunn-course/downloads and verify the release digest:

cd ~/underdunn-course/downloads
sha256sum overbooked-v1.0.0.tar

3b7aa3bee72c73a58cfe56e02ae3753e13f2e02897669e3e3ab2f51b05778153  overbooked-v1.0.0.tar

Don’t continue if it differs. Download a fresh copy and verify it again.

mkdir -p ~/underdunn-course/labs/overbooked
tar -xf overbooked-v1.0.0.tar -C ~/underdunn-course/labs/overbooked
cd ~/underdunn-course/labs/overbooked/overbooked-v1.0.0
sha256sum -c CHECKSUMS.sha256
sh build.sh

Every listed file has to report OK.

Freight booking desk.
Commands: book <crates>, stow <n>, desk, release, quit

The build is silent under -Wall -Wextra. The compiler has nothing to say about this one.

Safety note

Scope

Build and run only the program you build from this archive, inside the isolated course VM. The result is one line on standard output. You will not need to run code of your own, reach another process, or contact the network.

Do not brute force anything. Every value this challenge needs can be derived.

The flag

Paste exactly what the desk printed, with no surrounding whitespace:

Check your flag

Enter the complete flag, including UNDERDUNN{ and the closing brace. The check happens in your browser; the flag is not sent anywhere.

Check flag

Reset and cleanup

The desk keeps nothing between runs, so every process starts with nothing booked and no clearance. For a full reset of the files:

cd ~/underdunn-course/labs/overbooked
rm -rf -- overbooked-v1.0.0
tar -xf ~/underdunn-course/downloads/overbooked-v1.0.0.tar -C .
cd overbooked-v1.0.0
sha256sum -c CHECKSUMS.sha256
sh build.sh

Before resetting, copy any solver or modified source you want to keep outside the extraction. For final cleanup, remove the generated booking executable along with your own driver scripts, and keep both the verified archive and any work you want to revisit.