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

[Florian Westphal <fw@strlen.de>]

Maxim Mikityanskiy <maxtram95@gmail.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.
No need to send a v2, just saying.

Reviewed-by: Florian Westphal <fw@strlen.de>