_ Git - rust-lightning/blob - lightning/src/ln/onion_payment.rs

   1 //! Utilities to decode payment onions and do contextless validation of incoming payments.
   2 //!
   3 //! Primarily features [`peel_payment_onion`], which allows the decoding of an onion statelessly
   4 //! and can be used to predict whether we'd accept a payment.
   5
   6 use bitcoin::hashes::{Hash, HashEngine};
   7 use bitcoin::hashes::hmac::{Hmac, HmacEngine};
   8 use bitcoin::hashes::sha256::Hash as Sha256;
   9 use bitcoin::secp256k1::{self, PublicKey, Scalar, Secp256k1};
  10
  11 use crate::blinded_path;
  12 use crate::blinded_path::payment::{PaymentConstraints, PaymentRelay};
  13 use crate::chain::channelmonitor::{HTLC_FAIL_BACK_BUFFER, LATENCY_GRACE_PERIOD_BLOCKS};
  14 use crate::ln::PaymentHash;
  15 use crate::ln::channelmanager::{BlindedFailure, BlindedForward, CLTV_FAR_FAR_AWAY, HTLCFailureMsg, MIN_CLTV_EXPIRY_DELTA, PendingHTLCInfo, PendingHTLCRouting};
  16 use crate::ln::features::BlindedHopFeatures;
  17 use crate::ln::msgs;
  18 use crate::ln::onion_utils;
  19 use crate::ln::onion_utils::{HTLCFailReason, INVALID_ONION_BLINDING};
  20 use crate::sign::{NodeSigner, Recipient};
  21 use crate::util::logger::Logger;
  22
  23 #[allow(unused_imports)]
  24 use crate::prelude::*;
  25
  26 use core::ops::Deref;
  27
  28 /// Invalid inbound onion payment.
  29 #[derive(Debug)]
  30 pub struct InboundHTLCErr {
  31         /// BOLT 4 error code.
  32         pub err_code: u16,
  33         /// Data attached to this error.
  34         pub err_data: Vec<u8>,
  35         /// Error message text.
  36         pub msg: &'static str,
  37 }
  38
  39 fn check_blinded_payment_constraints(
  40         amt_msat: u64, cltv_expiry: u32, constraints: &PaymentConstraints
  41 ) -> Result<(), ()> {
  42         if amt_msat < constraints.htlc_minimum_msat ||
  43                 cltv_expiry > constraints.max_cltv_expiry
  44         { return Err(()) }
  45         Ok(())
  46 }
  47
  48 fn check_blinded_forward(
  49         inbound_amt_msat: u64, inbound_cltv_expiry: u32, payment_relay: &PaymentRelay,
  50         payment_constraints: &PaymentConstraints, features: &BlindedHopFeatures
  51 ) -> Result<(u64, u32), ()> {
  52         let amt_to_forward = blinded_path::payment::amt_to_forward_msat(
  53                 inbound_amt_msat, payment_relay
  54         ).ok_or(())?;
  55         let outgoing_cltv_value = inbound_cltv_expiry.checked_sub(
  56                 payment_relay.cltv_expiry_delta as u32
  57         ).ok_or(())?;
  58         check_blinded_payment_constraints(inbound_amt_msat, outgoing_cltv_value, payment_constraints)?;
  59
  60         if features.requires_unknown_bits_from(&BlindedHopFeatures::empty()) { return Err(()) }
  61         Ok((amt_to_forward, outgoing_cltv_value))
  62 }
  63
  64 pub(super) fn create_fwd_pending_htlc_info(
  65         msg: &msgs::UpdateAddHTLC, hop_data: msgs::InboundOnionPayload, hop_hmac: [u8; 32],
  66         new_packet_bytes: [u8; onion_utils::ONION_DATA_LEN], shared_secret: [u8; 32],
  67         next_packet_pubkey_opt: Option<Result<PublicKey, secp256k1::Error>>
  68 ) -> Result<PendingHTLCInfo, InboundHTLCErr> {
  69         debug_assert!(next_packet_pubkey_opt.is_some());
  70         let outgoing_packet = msgs::OnionPacket {
  71                 version: 0,
  72                 public_key: next_packet_pubkey_opt.unwrap_or(Err(secp256k1::Error::InvalidPublicKey)),
  73                 hop_data: new_packet_bytes,
  74                 hmac: hop_hmac,
  75         };
  76
  77         let (
  78                 short_channel_id, amt_to_forward, outgoing_cltv_value, intro_node_blinding_point
  79         ) = match hop_data {
  80                 msgs::InboundOnionPayload::Forward { short_channel_id, amt_to_forward, outgoing_cltv_value } =>
  81                         (short_channel_id, amt_to_forward, outgoing_cltv_value, None),
  82                 msgs::InboundOnionPayload::BlindedForward {
  83                         short_channel_id, payment_relay, payment_constraints, intro_node_blinding_point, features,
  84                 } => {
  85                         let (amt_to_forward, outgoing_cltv_value) = check_blinded_forward(
  86                                 msg.amount_msat, msg.cltv_expiry, &payment_relay, &payment_constraints, &features
  87                         ).map_err(|()| {
  88                                 // We should be returning malformed here if `msg.blinding_point` is set, but this is
  89                                 // unreachable right now since we checked it in `decode_update_add_htlc_onion`.
  90                                 InboundHTLCErr {
  91                                         msg: "Underflow calculating outbound amount or cltv value for blinded forward",
  92                                         err_code: INVALID_ONION_BLINDING,
  93                                         err_data: vec![0; 32],
  94                                 }
  95                         })?;
  96                         (short_channel_id, amt_to_forward, outgoing_cltv_value, intro_node_blinding_point)
  97                 },
  98                 msgs::InboundOnionPayload::Receive { .. } | msgs::InboundOnionPayload::BlindedReceive { .. } =>
  99                         return Err(InboundHTLCErr {
 100                                 msg: "Final Node OnionHopData provided for us as an intermediary node",
 101                                 err_code: 0x4000 | 22,
 102                                 err_data: Vec::new(),
 103                         }),
 104         };
 105
 106         Ok(PendingHTLCInfo {
 107                 routing: PendingHTLCRouting::Forward {
 108                         onion_packet: outgoing_packet,
 109                         short_channel_id,
 110                         blinded: intro_node_blinding_point.or(msg.blinding_point)
 111                                 .map(|bp| BlindedForward {
 112                                         inbound_blinding_point: bp,
 113                                         failure: intro_node_blinding_point
 114                                                 .map(|_| BlindedFailure::FromIntroductionNode)
 115                                                 .unwrap_or(BlindedFailure::FromBlindedNode),
 116                                 }),
 117                 },
 118                 payment_hash: msg.payment_hash,
 119                 incoming_shared_secret: shared_secret,
 120                 incoming_amt_msat: Some(msg.amount_msat),
 121                 outgoing_amt_msat: amt_to_forward,
 122                 outgoing_cltv_value,
 123                 skimmed_fee_msat: None,
 124         })
 125 }
 126
 127 pub(super) fn create_recv_pending_htlc_info(
 128         hop_data: msgs::InboundOnionPayload, shared_secret: [u8; 32], payment_hash: PaymentHash,
 129         amt_msat: u64, cltv_expiry: u32, phantom_shared_secret: Option<[u8; 32]>, allow_underpay: bool,
 130         counterparty_skimmed_fee_msat: Option<u64>, current_height: u32, accept_mpp_keysend: bool,
 131 ) -> Result<PendingHTLCInfo, InboundHTLCErr> {
 132         let (
 133                 payment_data, keysend_preimage, custom_tlvs, onion_amt_msat, onion_cltv_expiry,
 134                 payment_metadata, payment_context, requires_blinded_error
 135         ) = match hop_data {
 136                 msgs::InboundOnionPayload::Receive {
 137                         payment_data, keysend_preimage, custom_tlvs, sender_intended_htlc_amt_msat,
 138                         cltv_expiry_height, payment_metadata, ..
 139                 } =>
 140                         (payment_data, keysend_preimage, custom_tlvs, sender_intended_htlc_amt_msat,
 141                          cltv_expiry_height, payment_metadata, None, false),
 142                 msgs::InboundOnionPayload::BlindedReceive {
 143                         sender_intended_htlc_amt_msat, total_msat, cltv_expiry_height, payment_secret,
 144                         intro_node_blinding_point, payment_constraints, payment_context, keysend_preimage,
 145                         custom_tlvs
 146                 } => {
 147                         check_blinded_payment_constraints(
 148                                 sender_intended_htlc_amt_msat, cltv_expiry, &payment_constraints
 149                         )
 150                                 .map_err(|()| {
 151                                         InboundHTLCErr {
 152                                                 err_code: INVALID_ONION_BLINDING,
 153                                                 err_data: vec![0; 32],
 154                                                 msg: "Amount or cltv_expiry violated blinded payment constraints",
 155                                         }
 156                                 })?;
 157                         let payment_data = msgs::FinalOnionHopData { payment_secret, total_msat };
 158                         (Some(payment_data), keysend_preimage, custom_tlvs,
 159                          sender_intended_htlc_amt_msat, cltv_expiry_height, None, Some(payment_context),
 160                          intro_node_blinding_point.is_none())
 161                 }
 162                 msgs::InboundOnionPayload::Forward { .. } => {
 163                         return Err(InboundHTLCErr {
 164                                 err_code: 0x4000|22,
 165                                 err_data: Vec::new(),
 166                                 msg: "Got non final data with an HMAC of 0",
 167                         })
 168                 },
 169                 msgs::InboundOnionPayload::BlindedForward { .. } => {
 170                         return Err(InboundHTLCErr {
 171                                 err_code: INVALID_ONION_BLINDING,
 172                                 err_data: vec![0; 32],
 173                                 msg: "Got blinded non final data with an HMAC of 0",
 174                         })
 175                 }
 176         };
 177         // final_incorrect_cltv_expiry
 178         if onion_cltv_expiry > cltv_expiry {
 179                 return Err(InboundHTLCErr {
 180                         msg: "Upstream node set CLTV to less than the CLTV set by the sender",
 181                         err_code: 18,
 182                         err_data: cltv_expiry.to_be_bytes().to_vec()
 183                 })
 184         }
 185         // final_expiry_too_soon
 186         // We have to have some headroom to broadcast on chain if we have the preimage, so make sure
 187         // we have at least HTLC_FAIL_BACK_BUFFER blocks to go.
 188         //
 189         // Also, ensure that, in the case of an unknown preimage for the received payment hash, our
 190         // payment logic has enough time to fail the HTLC backward before our onchain logic triggers a
 191         // channel closure (see HTLC_FAIL_BACK_BUFFER rationale).
 192         if cltv_expiry <= current_height + HTLC_FAIL_BACK_BUFFER + 1 {
 193                 let mut err_data = Vec::with_capacity(12);
 194                 err_data.extend_from_slice(&amt_msat.to_be_bytes());
 195                 err_data.extend_from_slice(&current_height.to_be_bytes());
 196                 return Err(InboundHTLCErr {
 197                         err_code: 0x4000 | 15, err_data,
 198                         msg: "The final CLTV expiry is too soon to handle",
 199                 });
 200         }
 201         if (!allow_underpay && onion_amt_msat > amt_msat) ||
 202                 (allow_underpay && onion_amt_msat >
 203                  amt_msat.saturating_add(counterparty_skimmed_fee_msat.unwrap_or(0)))
 204         {
 205                 return Err(InboundHTLCErr {
 206                         err_code: 19,
 207                         err_data: amt_msat.to_be_bytes().to_vec(),
 208                         msg: "Upstream node sent less than we were supposed to receive in payment",
 209                 });
 210         }
 211
 212         let routing = if let Some(payment_preimage) = keysend_preimage {
 213                 // We need to check that the sender knows the keysend preimage before processing this
 214                 // payment further. Otherwise, an intermediary routing hop forwarding non-keysend-HTLC X
 215                 // could discover the final destination of X, by probing the adjacent nodes on the route
 216                 // with a keysend payment of identical payment hash to X and observing the processing
 217                 // time discrepancies due to a hash collision with X.
 218                 let hashed_preimage = PaymentHash(Sha256::hash(&payment_preimage.0).to_byte_array());
 219                 if hashed_preimage != payment_hash {
 220                         return Err(InboundHTLCErr {
 221                                 err_code: 0x4000|22,
 222                                 err_data: Vec::new(),
 223                                 msg: "Payment preimage didn't match payment hash",
 224                         });
 225                 }
 226                 if !accept_mpp_keysend && payment_data.is_some() {
 227                         return Err(InboundHTLCErr {
 228                                 err_code: 0x4000|22,
 229                                 err_data: Vec::new(),
 230                                 msg: "We don't support MPP keysend payments",
 231                         });
 232                 }
 233                 PendingHTLCRouting::ReceiveKeysend {
 234                         payment_data,
 235                         payment_preimage,
 236                         payment_metadata,
 237                         incoming_cltv_expiry: onion_cltv_expiry,
 238                         custom_tlvs,
 239                         requires_blinded_error,
 240                 }
 241         } else if let Some(data) = payment_data {
 242                 PendingHTLCRouting::Receive {
 243                         payment_data: data,
 244                         payment_metadata,
 245                         payment_context,
 246                         incoming_cltv_expiry: onion_cltv_expiry,
 247                         phantom_shared_secret,
 248                         custom_tlvs,
 249                         requires_blinded_error,
 250                 }
 251         } else {
 252                 return Err(InboundHTLCErr {
 253                         err_code: 0x4000|0x2000|3,
 254                         err_data: Vec::new(),
 255                         msg: "We require payment_secrets",
 256                 });
 257         };
 258         Ok(PendingHTLCInfo {
 259                 routing,
 260                 payment_hash,
 261                 incoming_shared_secret: shared_secret,
 262                 incoming_amt_msat: Some(amt_msat),
 263                 outgoing_amt_msat: onion_amt_msat,
 264                 outgoing_cltv_value: onion_cltv_expiry,
 265                 skimmed_fee_msat: counterparty_skimmed_fee_msat,
 266         })
 267 }
 268
 269 /// Peel one layer off an incoming onion, returning a [`PendingHTLCInfo`] that contains information
 270 /// about the intended next-hop for the HTLC.
 271 ///
 272 /// This does all the relevant context-free checks that LDK requires for payment relay or
 273 /// acceptance. If the payment is to be received, and the amount matches the expected amount for
 274 /// a given invoice, this indicates the [`msgs::UpdateAddHTLC`], once fully committed in the
 275 /// channel, will generate an [`Event::PaymentClaimable`].
 276 ///
 277 /// [`Event::PaymentClaimable`]: crate::events::Event::PaymentClaimable
 278 pub fn peel_payment_onion<NS: Deref, L: Deref, T: secp256k1::Verification>(
 279         msg: &msgs::UpdateAddHTLC, node_signer: &NS, logger: &L, secp_ctx: &Secp256k1<T>,
 280         cur_height: u32, accept_mpp_keysend: bool, allow_skimmed_fees: bool,
 281 ) -> Result<PendingHTLCInfo, InboundHTLCErr>
 282 where
 283         NS::Target: NodeSigner,
 284         L::Target: Logger,
 285 {
 286         let (hop, shared_secret, next_packet_details_opt) =
 287                 decode_incoming_update_add_htlc_onion(msg, node_signer, logger, secp_ctx
 288         ).map_err(|e| {
 289                 let (err_code, err_data) = match e {
 290                         HTLCFailureMsg::Malformed(m) => (m.failure_code, Vec::new()),
 291                         HTLCFailureMsg::Relay(r) => (0x4000 | 22, r.reason.data),
 292                 };
 293                 let msg = "Failed to decode update add htlc onion";
 294                 InboundHTLCErr { msg, err_code, err_data }
 295         })?;
 296         Ok(match hop {
 297                 onion_utils::Hop::Forward { next_hop_data, next_hop_hmac, new_packet_bytes } => {
 298                         let NextPacketDetails {
 299                                 next_packet_pubkey, outgoing_amt_msat: _, outgoing_scid: _, outgoing_cltv_value
 300                         } = match next_packet_details_opt {
 301                                 Some(next_packet_details) => next_packet_details,
 302                                 // Forward should always include the next hop details
 303                                 None => return Err(InboundHTLCErr {
 304                                         msg: "Failed to decode update add htlc onion",
 305                                         err_code: 0x4000 | 22,
 306                                         err_data: Vec::new(),
 307                                 }),
 308                         };
 309
 310                         if let Err((err_msg, code)) = check_incoming_htlc_cltv(
 311                                 cur_height, outgoing_cltv_value, msg.cltv_expiry
 312                         ) {
 313                                 return Err(InboundHTLCErr {
 314                                         msg: err_msg,
 315                                         err_code: code,
 316                                         err_data: Vec::new(),
 317                                 });
 318                         }
 319
 320                         // TODO: If this is potentially a phantom payment we should decode the phantom payment
 321                         // onion here and check it.
 322
 323                         create_fwd_pending_htlc_info(
 324                                 msg, next_hop_data, next_hop_hmac, new_packet_bytes, shared_secret,
 325                                 Some(next_packet_pubkey)
 326                         )?
 327                 },
 328                 onion_utils::Hop::Receive(received_data) => {
 329                         create_recv_pending_htlc_info(
 330                                 received_data, shared_secret, msg.payment_hash, msg.amount_msat, msg.cltv_expiry,
 331                                 None, allow_skimmed_fees, msg.skimmed_fee_msat, cur_height, accept_mpp_keysend,
 332                         )?
 333                 }
 334         })
 335 }
 336
 337 pub(super) struct NextPacketDetails {
 338         pub(super) next_packet_pubkey: Result<PublicKey, secp256k1::Error>,
 339         pub(super) outgoing_scid: u64,
 340         pub(super) outgoing_amt_msat: u64,
 341         pub(super) outgoing_cltv_value: u32,
 342 }
 343
 344 pub(super) fn decode_incoming_update_add_htlc_onion<NS: Deref, L: Deref, T: secp256k1::Verification>(
 345         msg: &msgs::UpdateAddHTLC, node_signer: &NS, logger: &L, secp_ctx: &Secp256k1<T>,
 346 ) -> Result<(onion_utils::Hop, [u8; 32], Option<NextPacketDetails>), HTLCFailureMsg>
 347 where
 348         NS::Target: NodeSigner,
 349         L::Target: Logger,
 350 {
 351         macro_rules! return_malformed_err {
 352                 ($msg: expr, $err_code: expr) => {
 353                         {
 354                                 log_info!(logger, "Failed to accept/forward incoming HTLC: {}", $msg);
 355                                 let (sha256_of_onion, failure_code) = if msg.blinding_point.is_some() {
 356                                         ([0; 32], INVALID_ONION_BLINDING)
 357                                 } else {
 358                                         (Sha256::hash(&msg.onion_routing_packet.hop_data).to_byte_array(), $err_code)
 359                                 };
 360                                 return Err(HTLCFailureMsg::Malformed(msgs::UpdateFailMalformedHTLC {
 361                                         channel_id: msg.channel_id,
 362                                         htlc_id: msg.htlc_id,
 363                                         sha256_of_onion,
 364                                         failure_code,
 365                                 }));
 366                         }
 367                 }
 368         }
 369
 370         if let Err(_) = msg.onion_routing_packet.public_key {
 371                 return_malformed_err!("invalid ephemeral pubkey", 0x8000 | 0x4000 | 6);
 372         }
 373
 374         let blinded_node_id_tweak = msg.blinding_point.map(|bp| {
 375                 let blinded_tlvs_ss = node_signer.ecdh(Recipient::Node, &bp, None).unwrap().secret_bytes();
 376                 let mut hmac = HmacEngine::<Sha256>::new(b"blinded_node_id");
 377                 hmac.input(blinded_tlvs_ss.as_ref());
 378                 Scalar::from_be_bytes(Hmac::from_engine(hmac).to_byte_array()).unwrap()
 379         });
 380         let shared_secret = node_signer.ecdh(
 381                 Recipient::Node, &msg.onion_routing_packet.public_key.unwrap(), blinded_node_id_tweak.as_ref()
 382         ).unwrap().secret_bytes();
 383
 384         if msg.onion_routing_packet.version != 0 {
 385                 //TODO: Spec doesn't indicate if we should only hash hop_data here (and in other
 386                 //sha256_of_onion error data packets), or the entire onion_routing_packet. Either way,
 387                 //the hash doesn't really serve any purpose - in the case of hashing all data, the
 388                 //receiving node would have to brute force to figure out which version was put in the
 389                 //packet by the node that send us the message, in the case of hashing the hop_data, the
 390                 //node knows the HMAC matched, so they already know what is there...
 391                 return_malformed_err!("Unknown onion packet version", 0x8000 | 0x4000 | 4);
 392         }
 393         macro_rules! return_err {
 394                 ($msg: expr, $err_code: expr, $data: expr) => {
 395                         {
 396                                 if msg.blinding_point.is_some() {
 397                                         return_malformed_err!($msg, INVALID_ONION_BLINDING)
 398                                 }
 399
 400                                 log_info!(logger, "Failed to accept/forward incoming HTLC: {}", $msg);
 401                                 return Err(HTLCFailureMsg::Relay(msgs::UpdateFailHTLC {
 402                                         channel_id: msg.channel_id,
 403                                         htlc_id: msg.htlc_id,
 404                                         reason: HTLCFailReason::reason($err_code, $data.to_vec())
 405                                                 .get_encrypted_failure_packet(&shared_secret, &None),
 406                                 }));
 407                         }
 408                 }
 409         }
 410
 411         let next_hop = match onion_utils::decode_next_payment_hop(
 412                 shared_secret, &msg.onion_routing_packet.hop_data[..], msg.onion_routing_packet.hmac,
 413                 msg.payment_hash, msg.blinding_point, node_signer
 414         ) {
 415                 Ok(res) => res,
 416                 Err(onion_utils::OnionDecodeErr::Malformed { err_msg, err_code }) => {
 417                         return_malformed_err!(err_msg, err_code);
 418                 },
 419                 Err(onion_utils::OnionDecodeErr::Relay { err_msg, err_code }) => {
 420                         return_err!(err_msg, err_code, &[0; 0]);
 421                 },
 422         };
 423
 424         let next_packet_details = match next_hop {
 425                 onion_utils::Hop::Forward {
 426                         next_hop_data: msgs::InboundOnionPayload::Forward {
 427                                 short_channel_id, amt_to_forward, outgoing_cltv_value
 428                         }, ..
 429                 } => {
 430                         let next_packet_pubkey = onion_utils::next_hop_pubkey(secp_ctx,
 431                                 msg.onion_routing_packet.public_key.unwrap(), &shared_secret);
 432                         NextPacketDetails {
 433                                 next_packet_pubkey, outgoing_scid: short_channel_id,
 434                                 outgoing_amt_msat: amt_to_forward, outgoing_cltv_value
 435                         }
 436                 },
 437                 onion_utils::Hop::Forward {
 438                         next_hop_data: msgs::InboundOnionPayload::BlindedForward {
 439                                 short_channel_id, ref payment_relay, ref payment_constraints, ref features, ..
 440                         }, ..
 441                 } => {
 442                         let (amt_to_forward, outgoing_cltv_value) = match check_blinded_forward(
 443                                 msg.amount_msat, msg.cltv_expiry, &payment_relay, &payment_constraints, &features
 444                         ) {
 445                                 Ok((amt, cltv)) => (amt, cltv),
 446                                 Err(()) => {
 447                                         return_err!("Underflow calculating outbound amount or cltv value for blinded forward",
 448                                                 INVALID_ONION_BLINDING, &[0; 32]);
 449                                 }
 450                         };
 451                         let next_packet_pubkey = onion_utils::next_hop_pubkey(&secp_ctx,
 452                                 msg.onion_routing_packet.public_key.unwrap(), &shared_secret);
 453                         NextPacketDetails {
 454                                 next_packet_pubkey, outgoing_scid: short_channel_id, outgoing_amt_msat: amt_to_forward,
 455                                 outgoing_cltv_value
 456                         }
 457                 },
 458                 onion_utils::Hop::Receive { .. } => return Ok((next_hop, shared_secret, None)),
 459                 onion_utils::Hop::Forward { next_hop_data: msgs::InboundOnionPayload::Receive { .. }, .. } |
 460                         onion_utils::Hop::Forward { next_hop_data: msgs::InboundOnionPayload::BlindedReceive { .. }, .. } =>
 461                 {
 462                         return_err!("Final Node OnionHopData provided for us as an intermediary node", 0x4000 | 22, &[0; 0]);
 463                 }
 464         };
 465
 466         Ok((next_hop, shared_secret, Some(next_packet_details)))
 467 }
 468
 469 pub(super) fn check_incoming_htlc_cltv(
 470         cur_height: u32, outgoing_cltv_value: u32, cltv_expiry: u32
 471 ) -> Result<(), (&'static str, u16)> {
 472         if (cltv_expiry as u64) < (outgoing_cltv_value) as u64 + MIN_CLTV_EXPIRY_DELTA as u64 {
 473                 return Err((
 474                         "Forwarding node has tampered with the intended HTLC values or origin node has an obsolete cltv_expiry_delta",
 475                         0x1000 | 13, // incorrect_cltv_expiry
 476                 ));
 477         }
 478         // Theoretically, channel counterparty shouldn't send us a HTLC expiring now,
 479         // but we want to be robust wrt to counterparty packet sanitization (see
 480         // HTLC_FAIL_BACK_BUFFER rationale).
 481         if cltv_expiry <= cur_height + HTLC_FAIL_BACK_BUFFER as u32 { // expiry_too_soon
 482                 return Err(("CLTV expiry is too close", 0x1000 | 14));
 483         }
 484         if cltv_expiry > cur_height + CLTV_FAR_FAR_AWAY as u32 { // expiry_too_far
 485                 return Err(("CLTV expiry is too far in the future", 21));
 486         }
 487         // If the HTLC expires ~now, don't bother trying to forward it to our
 488         // counterparty. They should fail it anyway, but we don't want to bother with
 489         // the round-trips or risk them deciding they definitely want the HTLC and
 490         // force-closing to ensure they get it if we're offline.
 491         // We previously had a much more aggressive check here which tried to ensure
 492         // our counterparty receives an HTLC which has *our* risk threshold met on it,
 493         // but there is no need to do that, and since we're a bit conservative with our
 494         // risk threshold it just results in failing to forward payments.
 495         if (outgoing_cltv_value) as u64 <= (cur_height + LATENCY_GRACE_PERIOD_BLOCKS) as u64 {
 496                 return Err(("Outgoing CLTV value is too soon", 0x1000 | 14));
 497         }
 498
 499         Ok(())
 500 }
 501
 502 #[cfg(test)]
 503 mod tests {
 504         use bitcoin::hashes::Hash;
 505         use bitcoin::hashes::sha256::Hash as Sha256;
 506         use bitcoin::secp256k1::{PublicKey, Secp256k1, SecretKey};
 507         use crate::ln::{PaymentPreimage, PaymentHash, PaymentSecret};
 508         use crate::ln::ChannelId;
 509         use crate::ln::channelmanager::RecipientOnionFields;
 510         use crate::ln::features::{ChannelFeatures, NodeFeatures};
 511         use crate::ln::msgs;
 512         use crate::ln::onion_utils::create_payment_onion;
 513         use crate::routing::router::{Path, RouteHop};
 514         use crate::util::test_utils;
 515
 516         #[test]
 517         fn fail_construct_onion_on_too_big_payloads() {
 518                 // Ensure that if we call `construct_onion_packet` and friends where payloads are too large for
 519                 // the allotted packet length, we'll fail to construct. Previously, senders would happily
 520                 // construct invalid packets by array-shifting the final node's HMAC out of the packet when
 521                 // adding an intermediate onion layer, causing the receiver to error with "final payload
 522                 // provided for us as an intermediate node."
 523                 let secp_ctx = Secp256k1::new();
 524                 let bob = crate::sign::KeysManager::new(&[2; 32], 42, 42);
 525                 let bob_pk = PublicKey::from_secret_key(&secp_ctx, &bob.get_node_secret_key());
 526                 let charlie = crate::sign::KeysManager::new(&[3; 32], 42, 42);
 527                 let charlie_pk = PublicKey::from_secret_key(&secp_ctx, &charlie.get_node_secret_key());
 528
 529                 let (
 530                         session_priv, total_amt_msat, cur_height, mut recipient_onion, keysend_preimage, payment_hash,
 531                         prng_seed, hops, ..
 532                 ) = payment_onion_args(bob_pk, charlie_pk);
 533
 534                 // Ensure the onion will not fit all the payloads by adding a large custom TLV.
 535                 recipient_onion.custom_tlvs.push((13377331, vec![0; 1156]));
 536
 537                 let path = Path { hops, blinded_tail: None, };
 538                 let onion_keys = super::onion_utils::construct_onion_keys(&secp_ctx, &path, &session_priv).unwrap();
 539                 let (onion_payloads, ..) = super::onion_utils::build_onion_payloads(
 540                         &path, total_amt_msat, recipient_onion, cur_height + 1, &Some(keysend_preimage)
 541                 ).unwrap();
 542
 543                 assert!(super::onion_utils::construct_onion_packet(
 544                                 onion_payloads, onion_keys, prng_seed, &payment_hash
 545                 ).is_err());
 546         }
 547
 548         #[test]
 549         fn test_peel_payment_onion() {
 550                 use super::*;
 551                 let secp_ctx = Secp256k1::new();
 552
 553                 let bob = crate::sign::KeysManager::new(&[2; 32], 42, 42);
 554                 let bob_pk = PublicKey::from_secret_key(&secp_ctx, &bob.get_node_secret_key());
 555                 let charlie = crate::sign::KeysManager::new(&[3; 32], 42, 42);
 556                 let charlie_pk = PublicKey::from_secret_key(&secp_ctx, &charlie.get_node_secret_key());
 557
 558                 let (session_priv, total_amt_msat, cur_height, recipient_onion, preimage, payment_hash,
 559                         prng_seed, hops, recipient_amount, pay_secret) = payment_onion_args(bob_pk, charlie_pk);
 560
 561                 let path = Path {
 562                         hops: hops,
 563                         blinded_tail: None,
 564                 };
 565
 566                 let (onion, amount_msat, cltv_expiry) = create_payment_onion(
 567                         &secp_ctx, &path, &session_priv, total_amt_msat, recipient_onion, cur_height,
 568                         &payment_hash, &Some(preimage), prng_seed
 569                 ).unwrap();
 570
 571                 let msg = make_update_add_msg(amount_msat, cltv_expiry, payment_hash, onion);
 572                 let logger = test_utils::TestLogger::with_id("bob".to_string());
 573
 574                 let peeled = peel_payment_onion(&msg, &&bob, &&logger, &secp_ctx, cur_height, true, false)
 575                         .map_err(|e| e.msg).unwrap();
 576
 577                 let next_onion = match peeled.routing {
 578                         PendingHTLCRouting::Forward { onion_packet, .. } => {
 579                                 onion_packet
 580                         },
 581                         _ => panic!("expected a forwarded onion"),
 582                 };
 583
 584                 let msg2 = make_update_add_msg(amount_msat, cltv_expiry, payment_hash, next_onion);
 585                 let peeled2 = peel_payment_onion(&msg2, &&charlie, &&logger, &secp_ctx, cur_height, true, false)
 586                         .map_err(|e| e.msg).unwrap();
 587
 588                 match peeled2.routing {
 589                         PendingHTLCRouting::ReceiveKeysend { payment_preimage, payment_data, incoming_cltv_expiry, .. } => {
 590                                 assert_eq!(payment_preimage, preimage);
 591                                 assert_eq!(peeled2.outgoing_amt_msat, recipient_amount);
 592                                 assert_eq!(incoming_cltv_expiry, peeled2.outgoing_cltv_value);
 593                                 let msgs::FinalOnionHopData{total_msat, payment_secret} = payment_data.unwrap();
 594                                 assert_eq!(total_msat, total_amt_msat);
 595                                 assert_eq!(payment_secret, pay_secret);
 596                         },
 597                         _ => panic!("expected a received keysend"),
 598                 };
 599         }
 600
 601         fn make_update_add_msg(
 602                 amount_msat: u64, cltv_expiry: u32, payment_hash: PaymentHash,
 603                 onion_routing_packet: msgs::OnionPacket
 604         ) -> msgs::UpdateAddHTLC {
 605                 msgs::UpdateAddHTLC {
 606                         channel_id: ChannelId::from_bytes([0; 32]),
 607                         htlc_id: 0,
 608                         amount_msat,
 609                         cltv_expiry,
 610                         payment_hash,
 611                         onion_routing_packet,
 612                         skimmed_fee_msat: None,
 613                         blinding_point: None,
 614                 }
 615         }
 616
 617         fn payment_onion_args(hop_pk: PublicKey, recipient_pk: PublicKey) -> (
 618                 SecretKey, u64, u32, RecipientOnionFields, PaymentPreimage, PaymentHash, [u8; 32],
 619                 Vec<RouteHop>, u64, PaymentSecret,
 620         ) {
 621                 let session_priv_bytes = [42; 32];
 622                 let session_priv = SecretKey::from_slice(&session_priv_bytes).unwrap();
 623                 let total_amt_msat = 1000;
 624                 let cur_height = 1000;
 625                 let pay_secret = PaymentSecret([99; 32]);
 626                 let recipient_onion = RecipientOnionFields::secret_only(pay_secret);
 627                 let preimage_bytes = [43; 32];
 628                 let preimage = PaymentPreimage(preimage_bytes);
 629                 let rhash_bytes = Sha256::hash(&preimage_bytes).to_byte_array();
 630                 let payment_hash = PaymentHash(rhash_bytes);
 631                 let prng_seed = [44; 32];
 632
 633                 // make a route alice -> bob -> charlie
 634                 let hop_fee = 1;
 635                 let recipient_amount = total_amt_msat - hop_fee;
 636                 let hops = vec![
 637                         RouteHop {
 638                                 pubkey: hop_pk,
 639                                 fee_msat: hop_fee,
 640                                 cltv_expiry_delta: 42,
 641                                 short_channel_id: 1,
 642                                 node_features: NodeFeatures::empty(),
 643                                 channel_features: ChannelFeatures::empty(),
 644                                 maybe_announced_channel: false,
 645                         },
 646                         RouteHop {
 647                                 pubkey: recipient_pk,
 648                                 fee_msat: recipient_amount,
 649                                 cltv_expiry_delta: 42,
 650                                 short_channel_id: 2,
 651                                 node_features: NodeFeatures::empty(),
 652                                 channel_features: ChannelFeatures::empty(),
 653                                 maybe_announced_channel: false,
 654                         }
 655                 ];
 656
 657                 (session_priv, total_amt_msat, cur_height, recipient_onion, preimage, payment_hash,
 658                         prng_seed, hops, recipient_amount, pay_secret)
 659         }
 660
 661 }