Skip to main content

Disposable VMs for Home Lab Security and Reproducibility

Today, various services (native, LXC, Docker) are running on my server. I'm mostly happy with the setup, but I decided to revisit my server's defenses under the assumption that a remote attacker or malicious code could compromise my services. A service might break out of its container or even gain root privilege.

VMs are a better security boundary than containers; they can limit the damage if an attacker gains root privilege. I cannot afford to run a dedicated VM for each service, so I will need to carefully group the services and run a dedicated VM for each group. Each group should be carefully designed based on the data accessed and the features/capabilities required. For example, some VMs may have access to my photos, while others may not have network access.


The Goal

There are two particular issues I want to address:

First, I want VM images to be easily reproducible, which makes backup and restore trivial. NixOS and GNU Guix System are great examples, where you only need to back up the configuration file. However, I don't really like them because of their domain-specific language/design.

Second, I want to seal the system as much as possible. Even a compromised root user inside a VM should not be able to permanently infect the VM. Many so-called "immutable" Linux distributions are not truly 100% immutable. Often, they just mean a read-only /usr. Some can be easily broken via `mount -o remount,rw`, and most of them allow self-upgrade, meaning a malicious root user can still inject code via "upgrade and reboot."

The Approach

I use bootc containers. This allows me to build the whole system with standard scripts, and it offers the standard "immutability."

Furthermore, I run QEMU with `--no-reboot --snapshot`, which means the system cannot update itself even with root privilege.

Lastly, I'll regularly build new images and restart the VM to pick up the latest security fixes.


This approach is essentially managing VMs like containers. It's not a new idea; frood and gokrazy are good examples of this principle.

On a side note, I also plan to learn more about KubeVirt and Nix VMs. Especially, I like the idea (from NixOS) that the guest can directly use the store from the host.

Notes about QEMU

Permanent machine-local data is stored in /var, which is put into a separate disk image.

Secrets are sent to QEMU via systemd credentials.

I tried virtiofsd, but didn't like it. I ended up with Samba anyway. Maybe I'll revisit virtiofsd later.

To shut down the VM (e.g., via systemd), I created a special admin user with special privilege defined in the sudoers file, so that I can run `ssh admin@vm sudo poweroff`. The SSH key pair is regenerated before each VM boot. Related: In a systemd unit, ExecStop= does not have access to LoadCredential.

I use `-chardev socket,logfile=...` and `-serial` so that the systemd logs are not filled with console output, and I can view or attach to the serial console later.

I plan to learn more about virtio-balloon and pmem later.

Conclusion

I find it very beneficial to deploy VMs. It allows me to shrink and harden the host OS (e.g., disable unprivileged user namespaces), and it allows me to design fine-grained access control.

Next, I'll start investigating how to organize the containers inside VMs. 

Labels:

Comments

Post a Comment

Popular posts from this blog

A Rocky Migration: Moving from docker-compose to Podman and gVisor

I've been running a few containers for several years. They were all running under rootless Docker with a single user. Initially, I planned to  migrate the containers to VMs , but I couldn't get a stable workflow after about two months of effort. Later,  gVisor caught my attention , and I decided to migrate to Podman with gVisor instead. The new plan is to run each container with  --userns=auto  and use Quadlet for systemd integration. This approach provides better isolation and makes writing firewall rules easier. I'm now close to migrating all my containers. Here are a couple of rough edges I'd like to share. Network Layout I compared  various networking options  and spent a few hours trying the one-interface-per-group approach before giving up. I settled on a single macvlan network and decided to use static IP addresses for my containers. To prevent a randomly assigned IP address from conflicting with a predefined one, I allocated a large IP range for my ...
Post a Comment
Read More »

GameConqueror 0.09 -- Linux Game Hacking Tool

If you are a game hacker If you've been looking for a `CheatEngine for Linux` Then you can't miss this. ============================================== GameConqueror is a game hacking tool for linux, it's written in PyGTK and uses scanmem as its backend. It's supposed to be with most useful features of CheatEngine for Linux. Currently, I've implemented almost everything about scanning, involving variant data types and scan types: Data Types: int{8/16/32/64}, float{32/64}, unknown type(int or float) and unknown width(will try each of them), byte array and string Scan Types: equal, greater, less, changed, unchanged, increased(by), decreased(by) This should be enough for most cases, so I decided to release it at the current status. ============================================= Here's how you can get it PPA (for Ubuntu users) https://launchpad.net/~coolwanglu/+archive/scanmem (I've not test it in 32bit environments or Jaunty, do please inform me if it doe...
Post a Comment
Read More »

Fix Google Security Code

Google Security Code (http://g.co/sc) is one type of 2-step verification. This is particularly useful when security keys and passkeys are not available. I have been using it in my LXC containers, until today I found out that it stopped working. It just kept saying "The code is invalid". It is easy to rule out some factors: The code works on other browsers on my laptop. The code works on other devices that are directly connected to the router. So it appears that Google also checks IP addresses besides the security code. Recently I have IPv6 enabled, so most devices that are directly connected to the router have both IPv4 and IPv6 addresses. But  I only enabled IPv4 for my LXC containers. So I guess when a code is generated by device A and used by device B, Google should be able to check that device A and device B are closely located. But in my case, IPv6 address appears on device A but not on device B, which may look suspicious. To fix the problem, I just needed to disable IPv...
Post a Comment
Read More »