From: Florian Westphal <fw@strlen.de>
To: Phil Sutter <phil@nwl.cc>,
Pablo Neira Ayuso <pablo@netfilter.org>,
Florian Westphal <fw@strlen.de>, Jan Engelhardt <jengelh@inai.de>,
netfilter-devel@vger.kernel.org
Subject: Re: [PATCH iptabes-nft] iptables-nft: allow removal of empty builtin chains
Date: Mon, 13 Sep 2021 18:02:20 +0200 [thread overview]
Message-ID: <20210913160220.GQ23554@breakpoint.cc> (raw)
In-Reply-To: <20210913154611.GB22465@orbyte.nwl.cc>
Phil Sutter <phil@nwl.cc> wrote:
> > Ok, so I will just send a simplified version of this patch that
> > will remove all empty basechains for -X too.
>
> I believe there was a misunderstanding: How I read Pablo's comments, he
> was walking about '-X' with base-chain name explicitly given. If a user
> calls e.g. 'iptables-nft -X FORWARD', it is clear that the new behaviour
> is intended and dropping any non-standard policy is not a surprise. The
> code right now though behaves unexpectedly:
>
> | # nft flush ruleset
> | # ./install/sbin/iptables-nft -P FORWARD DROP
> | # ./install/sbin/iptables-nft -X
> | # nft list ruleset
> | table ip filter {
> | }
>
> So forward DROP policy is lost even though the user just wanted to make
> sure any user-defined chains are gone. But things are worse in practice:
>
> | # iptables -A FORWARD -d 10.0.0.1 -j ACCEPT
> | # iptables -P FORWARD DROP
> | # iptables -X
>
> With iptables-nft, the last command above fails (EBUSY). I expect users
> to be pedantic when it comes to unexpected firewall openings or bogus
> errors in iptables-wrapping scripts.
>
> IMHO we're fine if chains with non-standard policy stay in place. Yet
> this might be racey because IIRC we don't have a "delete chain only if
> policy is accept" command flavour in kernel. This would be interesting,
> because we could drop a base chain also when it's flushed - just
> ignoring a rejected delete if it happens to be non-standard policy.
>
> The safe option should be to delete base chains only if given
> explicitly, as suggested by Pablo already I suppose.
No idea, I won't change anything. V1 kept '-X' behaviour as-is:
https://patchwork.ozlabs.org/project/netfilter-devel/patch/20210814174643.130760-1-fw@strlen.de/
see the "don't delete built-in chain" comment, the reject-check was kept
in place for the case where iptables-nft is iterating over all the
chains; explict '-X $NAME' was required.
So I don't know what I should change now. Feel free to update
as you see fit, including a revert.
prev parent reply other threads:[~2021-09-13 16:03 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-14 17:46 [PATCH iptabes-nft] iptables-nft: allow removal of empty builtin chains Florian Westphal
2021-08-14 20:18 ` Jan Engelhardt
2021-08-14 20:53 ` Florian Westphal
2021-08-15 13:12 ` Pablo Neira Ayuso
2021-08-15 13:27 ` Florian Westphal
2021-08-15 13:49 ` Pablo Neira Ayuso
2021-08-15 14:14 ` Florian Westphal
2021-08-15 14:27 ` Pablo Neira Ayuso
2021-08-15 14:36 ` Florian Westphal
2021-09-13 15:46 ` Phil Sutter
2021-09-13 16:02 ` Florian Westphal [this message]
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