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Date: Wed, 10 Dec 2025 16:14:49 +0100
From: Florian Westphal <fw@strlen.de>
To: Phil Sutter <phil@nwl.cc>
Cc: Pablo Neira Ayuso <pablo@netfilter.org>, Eric Garver <e@erig.me>,
	netfilter-devel@vger.kernel.org
Subject: Re: [nft PATCH v2] src: Convert ip {s,d}addr to IPv4-mapped as needed
Message-ID: <aTmOaUEmL0P_h0sy@strlen.de>
References: <20251210150333.14654-1-phil@nwl.cc>
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In-Reply-To: <20251210150333.14654-1-phil@nwl.cc>

Phil Sutter <phil@nwl.cc> wrote:
> Note that adding IPv4 addresses to sets of type ip6addr_type is still
> rejected although easily enabled by passing AI_V4MAPPED flag to
> getaddrinfo(): Since this also resolves DNS names, users may
> unexpectedly add a host's IPv4 address in mapped notation if the name
> doesn't resolve to an IPv6 address for whatever reason. If we really
> want to open this can of worms, it deserves a separate patch anyway.

I think we should force AI_NUMERICHOST when AI_V4MAPPED gets added, i.e.
never autofill in a v4mapped address for ip6addr_type when all we had
was a name.

> +# ip saddr ::ffff:1.2.3.4
> +ip test-ip4 input
> +  [ payload load 4b @ network header + 12 => reg 1 ]
> +  [ cmp eq reg 1 0x04030201 ]

Makes sense, no expansion.

> +# ip saddr @ip6addrset
> +ip test-ip4 input
> +  [ immediate reg 1 0x00000000 0x00000000 0xffff0000 ]
> +  [ payload load 4b @ network header + 12 => reg 11 ]
> +  [ lookup reg 1 set ip6addrset ]

Looks good to me, thanks for working on this.