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

submitted 8 months ago* (last edited 8 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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[–] zeluko@kbin.social 61 points 8 months ago (1 children)

Yeah, it needs those rules for e.g. port-forwarding into the containers.
But it doesnt really 'nuke' existing ones.

I have simply placed my rules at higher priority than normal. Very simple in nftables and good to not have rules mixed between nftables and iptables in unexpected ways.
You should filter as early as possible anyways to reduce ressource usage on e.g. connection tracking.

[–] Kalcifer@sh.itjust.works 3 points 8 months ago

But it doesnt really ‘nuke’ existing ones.

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.