netdev - Re: [PATCH net] netfilter: socket: Lookup orig tuple for IPv6 SNAT

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Message-ID: <Z9n00dy18IJHXdkK@calendula>
Date: Tue, 18 Mar 2025 23:33:53 +0100
From: Pablo Neira Ayuso <pablo@...filter.org>
To: Florian Westphal <fw@...len.de>
Cc: Maxim Mikityanskiy <maxtram95@...il.com>,
	Jozsef Kadlecsik <kadlec@...filter.org>,
	"David S. Miller" <davem@...emloft.net>,
	David Ahern <dsahern@...nel.org>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>, Patrick McHardy <kaber@...sh.net>,
	KOVACS Krisztian <hidden@...abit.hu>,
	Balazs Scheidler <bazsi@...abit.hu>,
	netfilter-devel@...r.kernel.org, coreteam@...filter.org,
	netdev@...r.kernel.org, Maxim Mikityanskiy <maxim@...valent.com>
Subject: Re: [PATCH net] netfilter: socket: Lookup orig tuple for IPv6 SNAT

On Tue, Mar 18, 2025 at 09:13:23PM +0100, Florian Westphal wrote:
> Maxim Mikityanskiy <maxtram95@...il.com> wrote:
> > nf_sk_lookup_slow_v4 does the conntrack lookup for IPv4 packets to
> > restore the original 5-tuple in case of SNAT, to be able to find the
> > right socket (if any). Then socket_match() can correctly check whether
> > the socket was transparent.
> > 
> > However, the IPv6 counterpart (nf_sk_lookup_slow_v6) lacks this
> > conntrack lookup, making xt_socket fail to match on the socket when the
> > packet was SNATed. Add the same logic to nf_sk_lookup_slow_v6.
> > 
> > IPv6 SNAT is used in Kubernetes clusters for pod-to-world packets, as
> > pods' addresses are in the fd00::/8 ULA subnet and need to be replaced
> > with the node's external address. Cilium leverages Envoy to enforce L7
> > policies, and Envoy uses transparent sockets. Cilium inserts an iptables
> > prerouting rule that matches on `-m socket --transparent` and redirects
> > the packets to localhost, but it fails to match SNATed IPv6 packets due
> > to that missing conntrack lookup.
> > 
> > Closes: https://github.com/cilium/cilium/issues/37932
> > Fixes: b64c9256a9b7 ("tproxy: added IPv6 support to the socket match")
> 
> Note that this commit predates IPv6 NAT support in netfilter.

Right. I am inclined to put this into nf-next.

> No need to send a v2, just saying.
> 
> Reviewed-by: Florian Westphal <fw@...len.de>

Thanks.