Context
I want to host public-facing applications on a server in my home, without compromising security. I realize containers might be one way to do this, and want to explore that route further.
Requirements
I want to run applications within containers such that they
- Must not be able to interfere with applications running on host
- Must not be able to interfere with other containers or applications inside them
- Must have no access or influence on other devices in the local network, or otherwise compromise the security of the network, but still accessible by devices via ssh.
Note: all of this within reason. I understand that sometimes there may be occasional vulnerabilities, like in kernel for example, that would eventually get fixed. Risks like this within reason I am willing to accept.
What I found so far
- Running containers in rootless mode: in other words, running the container daemon with an unprivileged host user
- Running applications in container under unprivileged users: the container user under which the container is ran should be unprivileged
- Networking: The container’s networking must be restricted. I am still not sure how to do this and shall explore it more, but would appreciate any resources.
Alternative solution
I have seen bubblewrap presented as an alternative, but it seems like it is not intended to be used directly in this manner, and information about using it for this is scarce.
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Running a container as an unprivileged user with podman is already quite good. Even if they break out of the container, the attacker will now be an unprivileged user. You’ll have to look up how to secure users in linux (I don’t know how).
As for networking, that’s where the firewall comes in.
iptablesare supposedly superseded bynftables. The easiest way to configure that is either with a GUI or withfirewalld. If I’m not mistaken, basically, what you want to do is limit the unprivileged user to creating a network namespace with a certain IP range (not sure if a virtual network device is created? probably). Then you can use the firewall to say:- allow all incoming and outgoing connections from the gateway (whatever device is exposed to the public internet through which your computer connects and receives traffic)
- block all connections outside of network namespace to IPs in your home network unless the connection was established from that IP. In other words your container won’t be able to connect to devices in your home network unless those devices initiated the connection themselves
You can find more information about
iptableson wikibooks. I cannot remember which table to use, but I think it’s the filter table.- rule1: INPUT chain ALLOW all from gateway
- rule2: OUTPUT chain ALLOW all to gateway
- rule3: INPUT chain ALLOW all from home network
- rule4: OUTPUT chain ALLOW all
ESTABLISHEDconnection to the home network
Can’t think of anything else. But it might help to draw a diagram with the network traffic flows.
Both Docker and Podman pretty much handle all of those so I think you’re good. The last aspect about networking can easily be fixed with a few iptables/nftables/firewalld rules. One final addition could be NGINX in front of web services or something dedicated to handling web requests on the open Internet to reduce potential exploits in the embedded web servers in your apps. But other than that, you’ve got it all covered yourself.
There’s all the options needed to limit CPU usage, memory usage or generally prevent using up all the system’s resources in docker/podman-compose files as well.
If you want an additional layer of security, you could also run it all in a VM, so a container escape leads to a VM that does nothing else but run containers. So another major layer to break.
Containers are meant to simplify operational aspects of development and deployment. For proper isolation you should use virtual machines.
By default a container runs with network, storage and resources isolated from the host. What about this isolation is not “proper”?
Because OP is looking for security isolation, which isn’t what containers are for. Much like an umbrella stops rain, but not bullets. You fool.
I still don’t understand why you think containers aren’t adequate.
Say you break into a container, how would you break out?
Kernel exploits. Containers logically isolate resources but they’re still effectively running as processes on the same kernel sharing the same hardware. There was one of those just last year: https://blog.aquasec.com/cve-2022-0185-linux-kernel-container-escape-in-kubernetes
Virtual machines are a whole other beast because the isolation is enforced at the hardware level, so you have to exploit hardware vulnerabilities like Spectre or a virtual device like a couple years ago some people found a breakout bug in the old floppy emulation driver that still gets assigned to VMs by default in QEMU.
You don’t design security solutions on the premise that they’re not working.
Security comes in layers, so if you’re serious about security you do in fact plan for things like that. You always want to limit the blast radius if your security measures fail. And most of the big cloud providers do that for their container/kubernetes offerings.
If you run portainer for example and that one gets breached, that’s essentially free container escape because you can trick Docker into mounting and exposing what you need from the host to escape. It’s not uncommon for people to sometimes give more permissions than the container really needs.
It’s not like making a VM dedicated to running your containers cost anything. It’s basically free. I don’t do it all the time, but if it’s exposed to the Internet and there’s other stuff on the box I want to be hard to get into, like if it runs on my home server or desktop, then it definitely gets a VM.
Otherwise, why even bother putting your apps in containers? You could also just make the apps themselves fully secure and unbreachable. Why do we need a container for isolation? One should assume the app’s security measures are working, right?
Easy solution: cloudflare tunnels
After you’ve gone through all the container hardening guides, cap off the exercise with OWASP’s docker recommendations.
Why does it need to be public-facing? There may be solutions that don’t require exposing it to billions of people.
Security is always about layers. The more independent layers there are, the fewer the chances someone will break through all of them. There is no one technology that will make your hosting reasonably secure, it’s the combination of multiple.
You’ve already mentioned software ran inside an unprivileged sandbox.
There’s also:
- Sandbox ran unprivileged inside a VM
- VM ran inside unprivileged sandbox
- Firewall only allowing applications to open certain ports
- Server running all of that hosted by someone else on their network with their own abstractions
My solution that took awhile to figure out is fantastic IMO. Docker containers unprivileged, with nobody permissions, with their own IPs on macvlan, with matching vlan and good firewall rules. A docker network proxy container, Traefik, Authelia, CrowdSec, and a CrowdSec Traefik Bouncer containers.
Disclaimer: I don’t know much about securing the container itself. The considerations I discuss here are mostly networking.
What I’ve personally been doing is using k3s with Cloudflare Tunnel (routed using DNS like in this documentation) as an ingress.
With Cloudflare Tunnel, if you create an application in front of it, you can require authentication and add a list of allowed emails.
I could replace k3s with a different Kubernetes distribution, and/or replace Cloudflare Tunnel with a different ingress (e.g., Tailscale Funnel or more common ingresses like nginx).
