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