rxrpc: Use the core ICMP/ICMP6 parsers

Make rxrpc_encap_rcv_err() pass the ICMP/ICMP6 skbuff to ip_icmp_error() or
ipv6_icmp_error() as appropriate to do the parsing rather than trying to do
it in rxrpc.

This pushes an error report onto the UDP socket's error queue and calls
->sk_error_report() from which point rxrpc can pick it up.

It would be preferable to steal the packet directly from ip*_icmp_error()
rather than letting it get queued, but this is probably good enough.

Also note that __udp4_lib_err() calls sk_error_report() twice in some
cases.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org

net/rxrpc/local_object.c

@@ -23,6 +23,19 @@
 static void rxrpc_local_processor(struct work_struct *);
 static void rxrpc_local_rcu(struct rcu_head *);
 
+/*
+ * Handle an ICMP/ICMP6 error turning up at the tunnel.  Push it through the
+ * usual mechanism so that it gets parsed and presented through the UDP
+ * socket's error_report().
+ */
+static void rxrpc_encap_err_rcv(struct sock *sk, struct sk_buff *skb, int err,
+				__be16 port, u32 info, u8 *payload)
+{
+	if (ip_hdr(skb)->version == IPVERSION)
+		return ip_icmp_error(sk, skb, err, port, info, payload);
+	return ipv6_icmp_error(sk, skb, err, port, info, payload);
+}
+
 /*
  * Compare a local to an address.  Return -ve, 0 or +ve to indicate less than,
  * same or greater than.