Document and test 0-len channel update onion error case

diff --git a/lightning/src/ln/onion_route_tests.rs b/lightning/src/ln/onion_route_tests.rs
index 8550532c69edd9a886d4c5851432323dd57d4398..785c11304ebbf2191c88843902c101ab39a299aa 100644 (file)
--- a/lightning/src/ln/onion_route_tests.rs
+++ b/lightning/src/ln/onion_route_tests.rs
@@ -645,6 +645,30 @@ fn test_onion_failure() {
                }, || nodes[2].node.fail_htlc_backwards(&payment_hash), false, None,
                Some(NetworkUpdate::NodeFailure { node_id: route.paths[0].hops[1].pubkey, is_permanent: true }),
                Some(channels[1].0.contents.short_channel_id));
+       run_onion_failure_test_with_fail_intercept("0-length channel update in UPDATE onion failure", 200, &nodes,
+               &route, &payment_hash, &payment_secret, |_msg| {}, |msg| {
+                       let session_priv = SecretKey::from_slice(&[3; 32]).unwrap();
+                       let onion_keys = onion_utils::construct_onion_keys(&Secp256k1::new(), &route.paths[0], &session_priv).unwrap();
+                       let mut decoded_err_packet = msgs::DecodedOnionErrorPacket {
+                               failuremsg: vec![
+                                       0x10, 0x7, // UPDATE|7
+                                       0x0, 0x0 // 0-len channel update
+                               ],
+                               pad: vec![0; 255 - 4 /* 4-byte error message */],
+                               hmac: [0; 32],
+                       };
+                       let um = onion_utils::gen_um_from_shared_secret(&onion_keys[1].shared_secret.as_ref());
+                       let mut hmac = HmacEngine::<Sha256>::new(&um);
+                       hmac.input(&decoded_err_packet.encode()[32..]);
+                       decoded_err_packet.hmac = Hmac::from_engine(hmac).into_inner();
+                       msg.reason = onion_utils::encrypt_failure_packet(
+                               &onion_keys[1].shared_secret.as_ref(), &decoded_err_packet.encode()[..])
+               }, || nodes[2].node.fail_htlc_backwards(&payment_hash), true, Some(0x1000|7),
+               Some(NetworkUpdate::ChannelFailure {
+                       short_channel_id: channels[1].0.contents.short_channel_id,
+                       is_permanent: false,
+               }),
+               Some(channels[1].0.contents.short_channel_id));
 }
 
 #[test]

diff --git a/lightning/src/ln/onion_utils.rs b/lightning/src/ln/onion_utils.rs
index 688a9c9617d93e636de1e8b6e2b601cd49a33bc6..64a1e3fa3487da78dc4918d17f56b57f8c99b085 100644 (file)
--- a/lightning/src/ln/onion_utils.rs
+++ b/lightning/src/ln/onion_utils.rs
@@ -579,6 +579,8 @@ where L::Target: Logger {
                                                                        msg: chan_update,
                                                                })
                                                        } else {
+                                                               // The node in question intentionally encoded a 0-length channel update. This is
+                                                               // likely due to https://github.com/ElementsProject/lightning/issues/6200.
                                                                network_update = Some(NetworkUpdate::ChannelFailure {
                                                                        short_channel_id: route_hop.short_channel_id,
                                                                        is_permanent: false,