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Comment by junon | Hacker News Reader

> automatically add a rule to open the firewall on linux

There's no way this is true. This completely defeats the purpose of a firewall.

If it is happening, then it's Docker doing this - not the linux firewall that comes stock with most distribution (iptables and the like). They would never simply add rules to the chains just because something was listening on that port.

Really, the best security advice for using Docker is to not use Docker. Unfortunately, there aren't very many "hold your hand" alternatives available. Aside from LXD and that family of technologies, which are criminally underused.

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Docker uses iptables for port forwarding, and those rules typically end up ahead of the rules inserted by your firewall (firewalld/ufw/manual scripts/whatever).

It's not so much that they explicitly open a firewall rule, as that they take a networking path that isn't really covered by traditional firewalls.

Another way of viewing it is that Docker "is" your firewall for your container workloads, and that adding a port-forward is equivalent to adding a firewall rule. Of course, that doesn't change that public-by-default is a bad default.

This is right, I remember now - docker does mangle your iptables chains. I remember fighting with this a while back.

Terrible practice, in my opinion. Docker shouldn't be touching firewall stuff.

Iptables magic is essential to how a lot of container networking stuff is implemented, though.

This is (imho) a huge flaw in the concept of a "container". I don't think most people comprehend how much crap is going on in the background.

For most container purposes, host networking and the default process namespace is absolutely fine, and reduces a lot of problems with interacting with containerized apps. 95% of the use case of containers is effectively just a chroot wrapper. If you need more features, this should be optional. This would also make rootless federated containerized apps just work. But nobody wants to go back to incremental features if Docker gives them everything at once.

If you think that’s bad, wait til you see what the iptables-save output is like on an istio-proxy sidecar ;)

Kubernetes as well. We ran into instances where iptables contention was so bad during outage recovery that things just stalled. iptables-save looked like a bomb went off.

I've resorted to adding my own firewall rules to the 'raw' table, which pretty much preempts all the rules Docker or the distribution inserts.

It's not as powerful as the later tables in the chain (see https://upload.wikimedia.org/wikipedia/commons/3/37/Netfilte... ) but a lot more robust.

This has been a major pain point for me. Despite my `firewalld` configuration only allowing specific traffic, all my containers were exposed.

My current policy is to set `"iptables": false` in Docker's `daemon.json` on any public machine. I don't understand why this isn't the default.

> My current policy is to set `"iptables": false` in Docker's `daemon.json` on any public machine. I don't understand why this isn't the default.

If you don't muck with iptables then you need a (slow) userspace proxy to expose your pods. That also means losing things like the source IP address for any incoming connections.

Interesting, I haven't noticed any slowdown, but I am running fairly low traffic services.

I do see that RemoteAddr is from a private IP range. Luckily I'm not using this information anywhere, but good to know.

If this is a surprise to you, scan your servers and see what else has helpful behavior which you didn’t expect. Services like shodan.io will even do this regularly and email you when things change.

It’s easy to blame Docker but I’ve seen this failure mode happen many times over the years - even experienced admins make mistakes. As always, defense in depth and continuous monitoring trumps raging about software.

I don't disagree with any of your points, but they aren't relevant to anything I've said. I never said Docker is the only one doing this. It's also not a surprise Docker in particular is doing this - Docker has a long history of doing bad things.

It is relevant because you said “there's no way this is true” when it is in fact true, which means that your understanding of how the system works doesn't match the actual behaviour. I mentioned the importance of scanning to catch those situations quickly.

I'm a Docker maintainer and have been for years.

The default is terrible. It got into 1.0 and just got stuck there :(

Changing defaults on such widely used software is, unfortunately, hard.

For whatever reason Docker prepends rules. There are things you can do to add your own filtering (Docker forwards to the "DOCKER-USER" chain where you can put your rules), but it requires people to know what is happening I order to use it securely.

It would be really nice to be in a more secure situation by default... open to suggestions and contributions for Docker 21.

Have you considered at least logging to the terminal on container start whenever a port gets exposed to the internet because of a 3306:3306 (i.e. without an explicit ip to bind to)? Part of the issue seems to be that people haven't read the docs and so don't really understand what that snippet they copied from that helpful blog, you know, does

I like this idea. I believe we already have a mechanism for warning on container create.

The nice thing is admins can already define a default value that the eninge will use to bind to (when no address is specified on -p). Warning can point users to that setting.

I do worry a bit about noise, though.

Perhaps make it easily quieted in the settings, and some kind of backoff between warnings? I definitely agree that it could be too much, on busy development systems especially!

What about a "docker secure" command which updates the configuration to a more secure default?

This also raises the possibility of different security profiles like dev, prod, etc.

A default Docker install would be documented as being for development, and you run "docker secure" to change that for other environments.

I like the general idea, but ultimately suffers the same problem in that people have to know about it. There actually is a setting to set the default bind address already.

If you can't change the default because of backwards compatibility and inertia, you can at least provide a well-documented, recommended, easy way of fixing the default.

Is there official documentation that tells users to set the default bind address as a best practice?

I wasn't thinking so much of just changing one setting, but rather having a way to easily reconfigure an installation to set multiple settings to improve security.

In addition, elevating this to the status of a command and documenting it as a best practice helps spread awareness.

That's definitely a tricky situation to be in since you'll inevitably get someone complaining that an upgrade broke something they depend on.

I like Godel_unicode's suggestion of logging and that could probably done in a stronger manner if there was some point (post-install, maybe starting a container) where it checked the existing rules and used a more prominent warning when there are existing rules which would prevent a container which would be reachable now from being reachable in the future. Given how widely Docker is used, I'd assume that'd be the kind of thing you'd need to add as a warning for multiple releases before even doing something like having it switch to a more secure default on new install.

It has to do with the implementation of the networking. The DOCKER chain in the nat table gets hit by inbound traffic on the PREROUTING chain before UFW's chains on the filter table. IIRC, can get around this by directing UFW to write its rules to the DOCKER-USER chain.

Firewalld is implemented differently and will exhibit the expected blocking behavior: traffic targeting docker ports will encounter firewalld before it encounters docker.

>Aside from LXD and that family of technologies, which are criminally underused.

Criminally underused indeed. I have no idea why it's not more popular for 'average' users/orgs. I don't know what issues may come up with scaling this up, but in our small org we've been running 20-30 (mostly unprivileged) LXD containers in production for several years now for all sorts of intranet and external-facing services (auth, DB, web, etc). Sure, it requires a bit more thought to set up than Docker, but it's well-documented (for most people's uses at least), secure, stable and lightweight.

>I have no idea why it's not more popular for 'average' users/orgs.

Maybe because many devs use Macs / Windows? Maybe WSL may tilt the balance in LXDs favour, but on OSX? Run it a VM yourself without the conveniences of docker-compose up?

As a Linuxuser myself, i looked at the competing solutions (podman, LXD, and the one by Canonical whose name i forgot) and thought: "Ain't gonna fly in a mixed environment."

They may be technologically superior, worse is better once again i guess. Would prefer them to Docker too.

Isn't docker running on OS X in VM anyway?

Yes it does, but it's very transparent - until you run into a few things that make it obvious, eg if you disk-image size limits, or memory limits.

I work with a few people who believed it was native, and used it for quite a while, until things started going wrong and we logged in to the vm to fix them.

Kinda my point. The reason docker is popular is simply that most of the devs are lazy, not very knowledgeable in the actual underlying technology and very short-sighted.

And docker marketing has very effectively used that to their advantage.

Yes it is, but docker for desktop runs it for you. You could use LXD etc by running Linux yourself in a virtualisation solution of your choice like VirtualBox or VMWare.

Yeah, that's my point.

On Linux you are going to run docker in VM anyway if you care a bit about security, but I know that almost all devs run docker directly on their laptops and with the user's full access to docker - ie. their user effectively becomes user. Without second thought ...

* becomes root, of course

> I have no idea why it's not more popular for 'average' users/orgs.

https://news.ycombinator.com/item?id=24782999 tongue in cheeck indeed, but better marketing it is, of course

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