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Wonderfall 2022-04-03 03:18:33 +02:00
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content/posts/docker-hardening.md
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@ -98,7 +98,7 @@ As mentioned just above, [user namespaces](https://www.man7.org/linux/man-pages/
"userns-remap": "default"
```
`whoami && sleep 60` in the container will return root, but `ps -fC sleep` on the host will show us the PID of another user. That is nice, but it has limitations and therefore shouldn't be considered as a real sandbox. In fact, the paradox is that [user namespaces are attack surface](https://lists.archlinux.org/pipermail/arch-general/2017-February/043066.html) (and vulnerabilities are still being found [years later](https://www.openwall.com/lists/oss-security/2022/01/29/1)), and it's common to restrict them to privileged users (`kernel.unprivileged_userns_clone=0`). That is fine for Docker with its traditional root daemon, but Podman expects you to let unprivileged users interact with user namespaces (so essentially privileged code).
`whoami && sleep 60` in the container will return root, but `ps -fC sleep` on the host will show us the PID of another user. That is nice, but it has limitations and therefore shouldn't be considered as a real sandbox. In fact, the paradox is that [user namespaces are attack surface](https://lists.archlinux.org/pipermail/arch-general/2017-February/043066.html) (and vulnerabilities are still being found [years later](https://www.openwall.com/lists/oss-security/2022/01/29/1)), and it's common wisdom to restrict them to privileged users (`kernel.unprivileged_userns_clone=0`). That is fine for Docker with its traditional root daemon, but Podman expects you to let unprivileged users interact with user namespaces (so essentially privileged code).
Enabling `userns-remap` in Docker shouldn't be a substitute for running unprivileged application containers (where applicable). User namespaces are mostly useful if you intend to run full-fledged OS containers which need root in order to function, but that is out of the scope of the container technologies mentioned in this article; for them, I'd argue exposing such a vulnerable attack surface from the host kernel for dubious sandboxing benefits isn't an interesting trade-off to make.
@ -220,7 +220,7 @@ Linux 4.4.0 is shown because that is the version of the Linux API that Sentry tr
## Conclusion: what's a container after all?
Like I wrote above, a container is mostly defined by its semantics and ecosystem. Containers shouldn't be solely defined by the OCI reference runtime implementation, as we've seen with gVisor that provides an entirely different security model.
Still not convinced? What if I told you a container can leverage the same technologies as a virtual machine? That is exactly what [Kata Containers](https://katacontainers.io/) does by using a VMM like QEMU-lite to provide containers that are in fact lightweight virtual machines, with their traditional resources and security model, compatibility with container semantics and toolset, and an optmized overhead. While not in the OCI ecosystem, Amazon achieves quite the same with [Firecracker](https://firecracker-microvm.github.io/).
Still not convinced? What if I told you a container can leverage the same technologies as a virtual machine? That is exactly what [Kata Containers](https://katacontainers.io/) does by using a VMM like QEMU-lite to provide containers that are in fact lightweight virtual machines, with their traditional resources and security model, compatibility with container semantics and toolset, and an optimized overhead. While not in the OCI ecosystem, Amazon achieves quite the same with [Firecracker](https://firecracker-microvm.github.io/).
If you're running untrusted workloads, I highly suggest you consider gVisor instead of a traditional container runtime. Your definition of "untrusted" may vary: for me, almost everything should be considered untrusted. That is how modern security works, and how mobile operating systems work. It's quite simple, security should be simple, and gVisor simply offers native security.