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Docker Targets

Each target must reside on its own directory under Dockerfiles/. Each target folder has the following structure

  • autoregister.yml An ansible playbook that is executed during the docker image build. Most of the times you dont have to modify this file.
  • Dockerfile This includes your standard Dockerfile instructions in order to build your target image
  • entrypoint.sh The script executed when the container starts
  • README.md A readme explaining the target, solution and other details (this is empty but you are advised to keep detailed records here as it will become harder to recall details the more targets you got)
  • variables.yml The variables used by the autoregister.yml playbook to do its job

You can use the existing Dockerfiles/example to get started or create your own.

Edit the file Dockerfiles/example/variables.yml and start by modifying the basic information.

ansible_host: 10.0.160.3
DOCKER: localhost
mac: "de:ad:be:ef:c0:ff:ee"
hostname: example
fqdn: example.echocity-f.com
rootable: 0 # 1 for yes
difficulty: 3
#scheduled_at: "YYYY-mm-dd HH:MM:SS"

The meaning and use of the variables is:

  • ansible_host the IP address that the container will be assigned. During development (eg while testing docker build) the default IP is usually one from the 172.17.0.0/24 subnet
  • DOCKER The docker host that will run this container (eg dockerd.example.net)
  • mac A valid and unique mac address. A nice trick to generate mac addresses for your hosts is to run something like the following
printf  "02:42:%.2x:%.2x:%.2x:%.2x\n" $(echo "IP_ADDRESS_OF_TARGET"|sed -e 's/\./ /g')
  • hostname and FQDN for the target. The hostname is also used as the container name when started
  • rootable Wether or not this target can be rooted or not 0=non-rootable and 1=rootable
  • difficulty A difficulty score for the target between 0 and 5. With 0 being the easiest and 5 harder
  • scheduled_at Uncomment to schedule this target to power up at a specific date and time

After the basic information, container specific details are included.

container:
  name: "{{hostname}}"
  hostname: "{{fqdn}}"
  build: "example" # The current folder name
  image: "example" # The current folder name
  state: "started"
  mac_address: "{{mac}}"
  purge_networks: "yes"
#  tag: "v0.1"
#  buildargs:
#   var_name: var_value
  env:
    ETSCTF_FLAG: "ETSCTF_{{ETSCTF_ENV_FLAG}}"
  dns_servers:
    - "10.0.0.254"
  networks:
    - { name: AAnet, ipv4_address: "{{ansible_host}}" }
  volumes: []

These details you need to modify include

  • build and image The folder that we are going to build the image from and the name that the intermediate image will have. When the images are pushed to a registry the name changes to hostname
  • tag A version/build tag. If no tag is defined then the default tag is latest
  • buildargs Key/Value pair of variables needed to build the container. More details about this can be found at docker –build-arg
  • env Key/Value environment variables defined upon starting a container. More details about the docker --env can be found at docker env variables
  • dns_servers A list of dns servers that the container will use for name resolution
  • networks The network this container will be attached. This is the same name as the one we created on our docker server (eg AAnet)
  • volumes A list of volumes to be mapped when the container starts

After that we can configure the core flags for /root, env, /etc/shadow and /etc/passsw

ETSCTF_ROOT_FLAG: ""
ETSCTF_ENV_FLAG: ""
ETSCTF_SHADOW_FLAG: ""
ETSCTF_PASSWD_FLAG: ""

We prefer to use random md5 hashes for these flags, but you can use whatever you like. The way we generate them is by using the password generator pwgen and piping its output to md5sum like so

pwgen|md5sum

One you have created all your docker targets prepare their hosts file we did with the dockers servers.

echo "[targets]"> inventories/targets/hosts
echo "example.fqdn.com">>inventories/targets/hosts

And add links from the variables.yml file of each container into the targets/host_vars like the following example

ln -s ../../../Dockerfiles/example/variables.yml inventories/targets/host_vars/example.fqdn.com.yml

NOTE: Ansible tries to access the example.fqdn.com.yml file relative to the inventories/targets/host_vars folder. You need to include the ../../../ part when creating the symbolic link for it to be able to find the variables.

Alternatively you can generate both hosts and their corresponding host_vars by running the following from the ansible folder.

INVENTORY="targets"
echo "[$INVENTORY]">inventories/$INVENTORY/hosts
for i in Dockerfiles/*;do
  fqdn=$(grep ^fqdn $i/variables.yml|awk '{print $2}')
  ln -fs ../../../$i/variables.yml inventories/$INVENTORY/host_vars/${fqdn}.yml
  echo -e "${fqdn}\t\t\t# "$(basename $i)>>inventories/$INVENTORY/hosts
done

In order to build the target images

ansible-playbook playbooks/build-images.yml -i inventories/targets --extra-vars "BUILDER=localhost" --extra-vars "DOCKER_REGISTRY=myregistry:5000" --extra-vars "DOCKER_REPOSITORY=targets"

Feed the data to the backend

ansible-playbook playbooks/feed-targets.yml -i inventories/targets  -e '{"mui":{"URL": "http://127.0.0.1:8080"}}'

You can also create a file at inventories/targets/group_vars/all.yml for the targets to include all those extra-vars details and not having to type them again

DOCKER_REGISTRY: "myregistry:5000"
DOCKER_REPOSITORY: "targets"
TOKEN: MyMUIToken
mui:
  URL: "{{MUI_URL|default('http://localhost:8080')}}"

Alternative build

You can also use the playbooks/build-squash.yml to build images with squashed layers. This however requires to add the option "experimental": true, to /etc/docker/daemon.json like so

{
  "experimental": true,
  "insecure-registries":["myregistry:5555"]
}

Once done restart the docker daemon for the changes to take effect and try to build your image

ansible-playbook playbooks/build-squash.yml -i inventories/targets

This playbook provides a few tags to ease in managing single tasks, such as * build: Build image * push: Push image to registry * rmi: Remove the image from local images

These tags can be used to perform a specific task or to skip some ie

ansible-playbook playbooks/build-squash.yml -i inventories/targets --skip-tags push,rmi