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PSA: Docker nukes your firewall rules and replaces them with its own. (sh.itjust.works)

submitted 9 months ago* (last edited 9 months ago) by Kalcifer@sh.itjust.works to c/selfhosted@lemmy.world

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I use nftables to set my firewall rules. I typically manually configure the rules myself. Recently, I just happened to dump the ruleset, and, much to my surprise, my config was gone, and it was replaced with an enourmous amount of extremely cryptic firewall rules. After a quick examination of the rules, I found that it was Docker that had modified them. And after some brief research, I found a number of open issues, just like this one, of people complaining about this behaviour. I think it's an enourmous security risk to have Docker silently do this by default.

I have heard that Podman doesn't suffer from this issue, as it is daemonless. If that is true, I will certainly be switching from Docker to Podman.

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[–] Kalcifer@sh.itjust.works 11 points 9 months ago (1 children)

How come I don't see my previous rules when I dump the ruleset, then? I have my rules written in /etc/nftables.conf, and they were previously applied by running # nft -f /etc/nftables.conf. Now, when I dump the current ruleset with # nft list ruleset, those previous rules aren't there — all I see are Docker's rules.

[–] gorgori@lemmy.world 1 points 9 months ago

You can use a bridge network or the host network.

In bridge network it is like a NAT host. With its own firewall settings.

In host network mode, it will just open the port it needs.