I am working on hardening our docker images, which I already have a bit of a weak understanding of. With that being said, the current step I am on is preventing the user from running the container as root. To me, that says "when a user runs 'docker exec -it my-container bash', he shall be an unprivileged user" (correct me if I'm wrong).
When I start up my container via docker-compose, the start script that is run needs to be as root since it deals with importing certs and mounted files (created externally and seen through a volume mount). After that is done, I would like the user to be 'appuser' for any future access. This question seems to match pretty well what I'm looking for, but I am using docker-compose, not docker run: How to disable the root access of a docker container?
This seems to be relevant, as the startup command differs from let's say tomcat. We are running a Spring Boot application that we start up with a simple 'java -jar jarFile', and the image is built using maven's dockerfile-maven-plugin. With that being said, should I be changing the user to an unprivileged user before running that, or still after?
I believe changing the user inside of the Dockerfile instead of the start script will do this... but then it will not run the start script as root, thus blowing up on calls that require root. I had messed with using ENTRYPOINT as well, but could have been doing it wrong there. Similarly, using "user:" in the yml file seemed to make the start.sh script run as that user instead of root, so that wasn't working.
Dockerfile:
FROM parent/image:latest
ENV APP_HOME /apphome
ENV APP_USER appuser
ENV APP_GROUP appgroup
# Folder containing our application, i.e. jar file, resources, and scripts.
# This comes from unpacking our maven dependency
ADD target/classes/app ${APP_HOME}/
# Primarily just our start script, but some others
ADD target/classes/scripts /scripts/
# Need to create a folder that will be used at runtime
RUN mkdir -p ${APP_HOME}/data && \
chmod +x /scripts/*.sh && \
chmod +x ${APP_HOME}/*.*
# Create unprivileged user
RUN groupadd -r ${APP_GROUP} && \
useradd -g ${APP_GROUP} -d ${APP_HOME} -s /sbin/nologin -c "Unprivileged User" ${APP_USER} && \
chown -R ${APP_USER}:${APP_GROUP} ${APP_HOME}
WORKDIR $APP_HOME
EXPOSE 8443
CMD /opt/scripts/start.sh
start.sh script:
#!/bin/bash
# setup SSL, modify java command, etc
# run our java application
java -jar "boot.jar"
# Switch users to always be unprivileged from here on out?
# Whatever "hardening" wants... Should this be before starting our application?
exec su -s "/bin/bash" $APP_USER
app.yml file:
version: '3.3'
services:
app:
image: app_image:latest
labels:
c2core.docker.compose.display-name: My Application
c2core.docker.compose.profiles: a_profile
volumes:
- "data_mount:/apphome/data"
- "cert_mount:/certs"
hostname: some-hostname
domainname: some-domain
ports:
- "8243:8443"
environment:
- some_env_vars
depends_on:
- another-app
networks:
a_network:
aliases:
- some-network
networks:
a_network:
driver: bridge
volumes:
data_mount:
cert_mount:
docker-compose shell script:
docker-compose -f app.yml -f another-app.yml $#
What I would expect is that anyone trying to access the container internally will be doing so as appuser and not root. The goal is to prevent someone from messing with things they shouldn't (i.e. docker itself).
What is happening is that the script will change users after the app has started (proven via an echo command), but it doesn't seem to be maintained. If I exec into it, I'm still root.
As David mentions, once someone has access to the docker socket (either via API or with the docker CLI), that typically means they have root access to your host. It's trivial to use that access to run a privileged container with host namespaces and volume mounts that let the attacker do just about anything.
When you need to initialize a container with steps that run as root, I do recommend gosu over something like su since su was not designed for containers and will leave a process running as the root pid. Make sure that you exec the call to gosu and that will eliminate anything running as root. However, the user you start the container as is the same as the user used for docker exec, and since you need to start as root, your exec will run as root unless you override it with a -u flag.
There are additional steps you can take to lock down docker in general:
Use user namespaces. These are defined on the entire daemon, require that you destroy all containers, and pull images again, since the uid mapping affects the storage of image layers. The user namespace offsets the uid's used by docker so that root inside the container is not root on the host, while inside the container you can still bind to low numbered ports and run administrative activities.
Consider authz plugins. Open policy agent and Twistlock are two that I know of, though I don't know if either would allow you to restrict the user of a docker exec command. They likely require that you give users a certificate to connect to docker rather than giving them direct access to the docker socket since the socket doesn't have any user details included in API requests it receives.
Consider rootless docker. This is still experimental, but since docker is not running as root, it has no access back to the host to perform root activities, mitigating many of the issues seen when containers are run as root.
You intrinsically can't prevent root-level access to your container.
Anyone who can run any Docker command at all can always run any of these three commands:
# Get a shell, as root, in a running container
docker exec -it -u 0 container_name /bin/sh
# Launch a new container, running a root shell, on some image
docker run --rm -it -u 0 --entrypoint /bin/sh image_name
# Get an interactive shell with unrestricted root access to the host
# filesystem (cd /host/var/lib/docker)
docker run --rm -it -v /:/host busybox /bin/sh
It is generally considered best practice to run your container as a non-root user, either with a USER directive in the Dockerfile or running something like gosu in an entrypoint script, like what you show. You can't prevent root access, though, in the face of a privileged user who's sufficiently interested in getting it.
When the docker is normally run from one host, you can do some steps.
Make sure it is not run from another host by looking for a secret in a directory mounted from the accepted host.
Change the .bashrc of the users on the host, so that they will start running the docker as soon as they login. When your users needs to do other things on the host, give them an account without docker access and let them sudo to a special user with docker access (or use a startdocker script with a setuid flag).
Start the docker with a script that you made and hardened, something like startserver.
#!/bin/bash
settings() {
# Add mount dirs. The homedir in the docker will be different from the one on the host.
mountdirs="-v /mirrored_home:/home -v /etc/dockercheck:/etc/dockercheck:ro"
usroptions="--user $(id -u):$(id -g) -v /etc/passwd:/etc/passwd:ro"
usroptions="${usroptions} -v/etc/shadow:/etc/shadow:ro -v /etc/group:/etc/group:ro"
}
# call function that fills special variables
settings
image="my_image:latest"
docker run -ti --rm ${usroptions} ${mountdirs} -w $HOME --entrypoint=/bin/bash "${image}"
Adding a variable --env HOSTSERVER=${host} won't help hardening, on another server one can add --env HOSTSERVER=servername_that_will_be_checked.
When the user logins to the host, the startserver will be called and the docker started. After the call to the startserver add exit to the .bash_rc.
Not sure if this work but you can try. Allow sudo access for user/group with limited execution command. Sudo configuration only allow to execute docker-cli. Create a shell script by the name docker-cli with content that runs docker command, eg docker "$#". In this file, check the argument and enforce user to provide switch --user or -u when executing exec or attach command of docker. Also make sure validate the user don't provide a switch saying -u root. Eg
sudo docker-cli exec -it containerid sh (failed)
sudo docker-cli exec -u root ... (failed)
sudo docker-cli exec -u mysql ... (Passed)
You can even limit the docker command a user can run inside this shell script
I'm trying to create an EC2 User-data script to run other scripts on boot up. However, the scripts that I run fail to recognize some commands and variables that I'd already declared. I'm running the commands as the "ubuntu" user but it still isn't working.
My user-data script looks something like this:
export user="ubuntu"
sudo su $user -c ". ./run_script"
Within the script, I have these lines:
THIS_PATH="/some/path"
echo "export SOME_PATH=$THIS_PATH" >> ~/.bashrc
source ~/.bashrc
However, the script can't run SOME_PATH/application, and echo $SOME_PATH this returns a blank line. I'm confused because $SOME_PATH/application works when I log into the EC2 using SSH and my debug logs using whoami returns "ubuntu."
Am I missing something here?
Your data script is executed as root and su command leaves $HOME and other ENV variables intact (note that sudo is redundant). "su -" does not help either
So, do not use ~ or $HOME but full path /home/ubuntu/.bashrc
I found out the problem. It seems that source ~/.bashrc isn't enough to restart the shell -- the environment variables worked after I referenced them in another bash script.
I have a script (hosted on GitHub) that does the following:
Creates an EC2 instance on AWS
Saves the local IP (private IP address) as an environment variable $LOCALIP
Installs Docker (official repo)
Updates the base instance (Ubuntu 16.04 LTS)
Pulls a custom image of mine
Runs said image with the -e LOCALIP trying to pass the hosts environment variable to the container (I have also tried -e LOCALIP=$LOCALIP
However when I docker exec into the container on that instance and run echo $LOCALIP it displays nothing. Running env shows me that LOCALIP is there but nothing is against it
If I destroy the container and remake using the exact same line from the original script (with -e LOCALIP=$LOCALIP) it works - I need this process automating however and some additional help would be greatly appreciated.
Essentially sudo docker run -dit -e LOCALIP -p 1099:1099 -p 50000:50000 screamingjoypad/armada-server /bin/bash is not sharing the hosts LOCALIP variable.
UPDATE
Trying the suggestions from below I added the following line to my script
source /etc/bash.bashrc but this still does not work. I'm still getting a blank when trying the echo $LOCALIP in the container...
The problem is because of this line of your shell script:
echo "export LOCALIP=$(hostname -i)" >> /etc/bash.bashrc
After this command is executed, the export instruction does not take effect yet. It will take effect after your next login.
To make the LOCALIP environment variable take effect immediately, add this line after the echo "export ... command:
source /etc/bash.bashrc
I believe I've solved it. I'm now using the AWS metadata to harvest the private IP address using the following addition to the script:
sudo docker run -dit -e LOCALIP=$(curl http://169.254.169.254/latest/meta-data/local-ipv4) -p 1099:1099 -p 50000:50000 screamingjoypad/armada-server /bin/bash
I am attempting to run 3 Docker images, MySQL, Redis and a project of mine on Bash for Windows (WSL).
To do that I have to connect to the Docker engine running on Windows, specifically on tcp://locahost:2375. I have appended the following line to .bashrc:
export DOCKER_HOST=tcp://127.0.0.1:2375
I can successfully run docker commands like docker ps or docker run hello-world but whenever I cd into my project directory and run
sudo docker-compose up --build to load the images and spin up the containers I get an error:
ERROR: Couldn't connect to Docker daemon at http+docker://localunixsocket - is it running?
If it's at a non-standard location, specify the URL with the DOCKER_HOST environment variable.
I know that if I use the -H argument I can supply the address but I'd rather find a more permanent solution. For some reason docker-compose seems to ignore the DOCKER_HOST environmental variable and I can't figure out why..
Your problem is sudo. It's a totally different program than your shell and doesn't transfer the exported environment unless you specifically tell it to. You can either add the following line in your /etc/sudoers (or /etc/sudoers.d/docker):
Defaults env_keep += DOCKER_HOST
Or you can just pass it directly to the command line:
sudo DOCKER_HOST=$DOCKER_HOST docker-compose up --build
By set DOCKER_HOST you tell for every run of docker in command line to use http api, instead of default - socket on localhost.
By default http api is not turned on
$ sudo cat /lib/systemd/system/docker.service | grep ExecStart
ExecStart=/usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock
you can add -H tcp://127.0.0.1:2375 for tern on http api on localhost
but usually you want to tern on api for remote servers by -H tcp://0.0.0.0:2375 (do it only with proper firewall)
so you need to change in /lib/systemd/system/docker.service to next line
ExecStart=/usr/bin/dockerd -H fd:// -H tcp://127.0.0.1:2375 --containerd=/run/containerd/containerd.sock
From examples I've seen one can set environment variables in docker-compose.yml like so:
services:
postgres:
image: my_node_app
ports: -8080:8080
environment:
APP_PASSWORD: mypassword
...
For security reasons, my use case requires me to fetch the password from a server that we have a bash client for:
#!/bin/bash
get_credential <server> <dev-environment> <role> <key>
In docker documentation, I found this, which says that I can pass in shell environment variable values to docker compose. So I can run the bash client to grab the passwords in my starting shell that creates the docker instances. However, that requires me to have my bash client outside docker and inside my maven project.
Another way to do this would be to run/cmd/entrypoint a bash script that can set environment variable for the docker instance. Since my docker image runs node.js, currently my Dockerfile is like this:
FROM node:4-slim
MAINTAINER myself
# ... do Dockerfile stuff
# TRIAL #1: run a bash script to set the environment varable --- UNSUCCESSFUL!
COPY set_en_var.sh /
RUN chmod +x /set_en_var.sh
RUN /bin/bash /set_en_var.sh
# original entry point
#ENTRYPOINT ["node", "mynodeapp.js", "configuration.js"]
# TRIAL #2: use a bash script as entrypoint that sets
# the environment variable and runs my node app . --- UNSUCCESSFUL TOO!
ENTRYPOINT ["/entrypoint.sh"]
Here is the code for entrypoint.sh:
. mybashclient.sh
cred_str=$(get_credential <server> <dev-environment> <role> <key>)
export APP_PASSWORD=( $cred_str )
# run the original entrypoint command
node mynodeapp.js configuration.js
And here is code for my set_en_var.sh:
. mybashclient.sh
cred_str=$(get_credential <server> <dev-environment> <role> <key>
export APP_PASSWORD=( $cred_str )
So 2 questions:
Which is a better choice, having my bash client for password live inside docker or outside docker?
If I were to have it inside docker, how can I use cmd/run/entrypoint to achieve this?
Which is a better choice, having my bash client for password live inside docker or outside docker?
Always have it inside. You don't want dependencies on the host OS. You want to avoid that situation as much as possible
If I were to have it inside docker, how can I use cmd/run/entrypoint to achieve this?
Consider the below line of code you used
RUN /bin/bash /set_en_var.sh
This won't work at all. Because you don't make any change to the docker container as such. You just run a bash which gets some environment variables and then the bash exits and nothing on the OS gets changes. Dockerfile build will only maintain changes that happened to the OS from that command. And in your case except for that session of the bash, nothing changes.
Next your approach to do this during the build time is also not justified. If you build it with the environment variables inside it then you are breaking the purpose of having a command to fetch the latest credentials. Suppose your change the password, then this would require you to rebuild the image (in case it had worked)
Now your entrypoint.sh approach is the right one and it should work. You should just check what is going wrong with it. Also echo the cred_str for your testing to make sure you are getting the right credentials detail back from the command
Last you should change the line
node mynodeapp.js configuration.js
to
exec node mynodeapp.js configuration.js
This makes sure that your node process becomes the PID 1.