linux-kernel - Re: [PATCH] netfilter: xt_NFLOG: allow 128 character log prefixes

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Message-ID: <20210727230230.GA30104@salvia>
Date:   Wed, 28 Jul 2021 01:02:30 +0200
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     Alex Forster <aforster@...udflare.com>
Cc:     Kyle Bowman <kbowman@...udflare.com>,
        kernel-team <kernel-team@...udflare.com>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        Florian Westphal <fw@...len.de>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        linux-kernel@...r.kernel.org,
        Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH] netfilter: xt_NFLOG: allow 128 character log prefixes

On Tue, Jul 27, 2021 at 05:45:09PM -0500, Alex Forster wrote:
> > Yes, you can update iptables-nft to use nft_log instead of xt_LOG,
> > that requires no kernel upgrades and it will work with older kernels.
> 
> I've always been under the impression that mixing xtables and nftables
> was impossible. Forgive me, but I just want to clarify one more time:
> you're saying we should be able to modify iptables-nft such that the
> following rule will use xt_bpf to match a packet and then nft_log to
> log it, rather than xt_log as it does today?

You could actually use *any* of the existing extensions to match a
packet, the matching side is completely irrelevant to this picture.

As I said, userspace iptables-nft can be updated to use nft_log
instead of xt_LOG.

>     iptables-nft -A test-chain -d 11.22.33.44/32 -m bpf --bytecode
> "1,6 0 0 65536" -j NFLOG --nflog-prefix
> "0123456789012345678901234567890123456789012345678901234567890123456789"
> 
> We had some unexplained performance loss when we were evaluating
> switching to iptables-nft, but if this sort of mixing is possible then
> it is certainly worth reevaluating.