Merge pull request #2570 from valentinewallace/2023-08-router-fuzz-fail
authorMatt Corallo <649246+TheBlueMatt@users.noreply.github.com>
Wed, 27 Sep 2023 20:40:32 +0000 (20:40 +0000)
committerGitHub <noreply@github.com>
Wed, 27 Sep 2023 20:40:32 +0000 (20:40 +0000)
Fix router fuzz failure

lightning/src/routing/router.rs

index 92e5dadf979e391371d8dd05d4a5258c73238184..09d83bb785cdfe1d9ac2786cce278311a6279648 100644 (file)
@@ -1265,7 +1265,11 @@ impl<'a> PaymentPath<'a> {
        // Note that this function is not aware of the available_liquidity limit, and thus does not
        // support increasing the value being transferred beyond what was selected during the initial
        // routing passes.
-       fn update_value_and_recompute_fees(&mut self, value_msat: u64) {
+       //
+       // Returns the amount that this path contributes to the total payment value, which may be greater
+       // than `value_msat` if we had to overpay to meet the final node's `htlc_minimum_msat`.
+       fn update_value_and_recompute_fees(&mut self, value_msat: u64) -> u64 {
+               let mut extra_contribution_msat = 0;
                let mut total_fee_paid_msat = 0 as u64;
                for i in (0..self.hops.len()).rev() {
                        let last_hop = i == self.hops.len() - 1;
@@ -1280,6 +1284,7 @@ impl<'a> PaymentPath<'a> {
 
                        let cur_hop = &mut self.hops.get_mut(i).unwrap().0;
                        cur_hop.next_hops_fee_msat = total_fee_paid_msat;
+                       cur_hop.path_penalty_msat += extra_contribution_msat;
                        // Overpay in fees if we can't save these funds due to htlc_minimum_msat.
                        // We try to account for htlc_minimum_msat in scoring (add_entry!), so that nodes don't
                        // set it too high just to maliciously take more fees by exploiting this
@@ -1295,8 +1300,15 @@ impl<'a> PaymentPath<'a> {
                                // Also, this can't be exploited more heavily than *announce a free path and fail
                                // all payments*.
                                cur_hop_transferred_amount_msat += extra_fees_msat;
-                               total_fee_paid_msat += extra_fees_msat;
-                               cur_hop_fees_msat += extra_fees_msat;
+
+                               // We remember and return the extra fees on the final hop to allow accounting for
+                               // them in the path's value contribution.
+                               if last_hop {
+                                       extra_contribution_msat = extra_fees_msat;
+                               } else {
+                                       total_fee_paid_msat += extra_fees_msat;
+                                       cur_hop_fees_msat += extra_fees_msat;
+                               }
                        }
 
                        if last_hop {
@@ -1324,6 +1336,7 @@ impl<'a> PaymentPath<'a> {
                                }
                        }
                }
+               value_msat + extra_contribution_msat
        }
 }
 
@@ -1489,6 +1502,9 @@ where L::Target: Logger {
        if payee_node_id_opt.map_or(false, |payee| payee == our_node_id) {
                return Err(LightningError{err: "Cannot generate a route to ourselves".to_owned(), action: ErrorAction::IgnoreError});
        }
+       if our_node_id == maybe_dummy_payee_node_id {
+               return Err(LightningError{err: "Invalid origin node id provided, use a different one".to_owned(), action: ErrorAction::IgnoreError});
+       }
 
        if final_value_msat > MAX_VALUE_MSAT {
                return Err(LightningError{err: "Cannot generate a route of more value than all existing satoshis".to_owned(), action: ErrorAction::IgnoreError});
@@ -1707,13 +1723,13 @@ where L::Target: Logger {
                // Adds entry which goes from $src_node_id to $dest_node_id over the $candidate hop.
                // $next_hops_fee_msat represents the fees paid for using all the channels *after* this one,
                // since that value has to be transferred over this channel.
-               // Returns whether this channel caused an update to `targets`.
+               // Returns the contribution amount of $candidate if the channel caused an update to `targets`.
                ( $candidate: expr, $src_node_id: expr, $dest_node_id: expr, $next_hops_fee_msat: expr,
                        $next_hops_value_contribution: expr, $next_hops_path_htlc_minimum_msat: expr,
                        $next_hops_path_penalty_msat: expr, $next_hops_cltv_delta: expr, $next_hops_path_length: expr ) => { {
                        // We "return" whether we updated the path at the end, and how much we can route via
                        // this channel, via this:
-                       let mut did_add_update_path_to_src_node = None;
+                       let mut hop_contribution_amt_msat = None;
                        // Channels to self should not be used. This is more of belt-and-suspenders, because in
                        // practice these cases should be caught earlier:
                        // - for regular channels at channel announcement (TODO)
@@ -1781,6 +1797,7 @@ where L::Target: Logger {
                                                CandidateRouteHop::FirstHop { .. } => true,
                                                CandidateRouteHop::PrivateHop { .. } => true,
                                                CandidateRouteHop::Blinded { .. } => true,
+                                               CandidateRouteHop::OneHopBlinded { .. } => true,
                                                _ => false,
                                        };
 
@@ -1815,10 +1832,11 @@ where L::Target: Logger {
                                                // might violate htlc_minimum_msat on the hops which are next along the
                                                // payment path (upstream to the payee). To avoid that, we recompute
                                                // path fees knowing the final path contribution after constructing it.
-                                               let path_htlc_minimum_msat = cmp::max(
-                                                       compute_fees_saturating($next_hops_path_htlc_minimum_msat, $candidate.fees())
-                                                               .saturating_add($next_hops_path_htlc_minimum_msat),
-                                                       $candidate.htlc_minimum_msat());
+                                               let curr_min = cmp::max(
+                                                       $next_hops_path_htlc_minimum_msat, $candidate.htlc_minimum_msat()
+                                               );
+                                               let path_htlc_minimum_msat = compute_fees_saturating(curr_min, $candidate.fees())
+                                                       .saturating_add(curr_min);
                                                let hm_entry = dist.entry($src_node_id);
                                                let old_entry = hm_entry.or_insert_with(|| {
                                                        // If there was previously no known way to access the source node
@@ -1926,7 +1944,7 @@ where L::Target: Logger {
                                                                        {
                                                                                old_entry.value_contribution_msat = value_contribution_msat;
                                                                        }
-                                                                       did_add_update_path_to_src_node = Some(value_contribution_msat);
+                                                                       hop_contribution_amt_msat = Some(value_contribution_msat);
                                                                } else if old_entry.was_processed && new_cost < old_cost {
                                                                        #[cfg(all(not(ldk_bench), any(test, fuzzing)))]
                                                                        {
@@ -1961,7 +1979,7 @@ where L::Target: Logger {
                                        }
                                }
                        }
-                       did_add_update_path_to_src_node
+                       hop_contribution_amt_msat
                } }
        }
 
@@ -2079,7 +2097,7 @@ where L::Target: Logger {
                                // in the regular network graph.
                                first_hop_targets.get(&intro_node_id).is_some() ||
                                network_nodes.get(&intro_node_id).is_some();
-                       if !have_intro_node_in_graph { continue }
+                       if !have_intro_node_in_graph || our_node_id == intro_node_id { continue }
                        let candidate = if hint.1.blinded_hops.len() == 1 {
                                CandidateRouteHop::OneHopBlinded { hint, hint_idx }
                        } else { CandidateRouteHop::Blinded { hint, hint_idx } };
@@ -2098,9 +2116,10 @@ where L::Target: Logger {
                                                Some(fee) => fee,
                                                None => continue
                                        };
+                                       let path_min = candidate.htlc_minimum_msat().saturating_add(
+                                               compute_fees_saturating(candidate.htlc_minimum_msat(), candidate.fees()));
                                        add_entry!(first_hop_candidate, our_node_id, intro_node_id, blinded_path_fee,
-                                               path_contribution_msat, candidate.htlc_minimum_msat(), 0_u64,
-                                               candidate.cltv_expiry_delta(),
+                                               path_contribution_msat, path_min, 0_u64, candidate.cltv_expiry_delta(),
                                                candidate.blinded_path().map_or(1, |bp| bp.blinded_hops.len() as u8));
                                }
                        }
@@ -2200,11 +2219,15 @@ where L::Target: Logger {
                                                .map_or(None, |inc| inc.checked_add(aggregate_next_hops_fee_msat));
                                        aggregate_next_hops_fee_msat = if let Some(val) = hops_fee { val } else { break; };
 
-                                       let hop_htlc_minimum_msat = candidate.htlc_minimum_msat();
-                                       let hop_htlc_minimum_msat_inc = if let Some(val) = compute_fees(aggregate_next_hops_path_htlc_minimum_msat, hop.fees) { val } else { break; };
-                                       let hops_path_htlc_minimum = aggregate_next_hops_path_htlc_minimum_msat
-                                               .checked_add(hop_htlc_minimum_msat_inc);
-                                       aggregate_next_hops_path_htlc_minimum_msat = if let Some(val) = hops_path_htlc_minimum { cmp::max(hop_htlc_minimum_msat, val) } else { break; };
+                                       // The next channel will need to relay this channel's min_htlc *plus* the fees taken by
+                                       // this route hint's source node to forward said min over this channel.
+                                       aggregate_next_hops_path_htlc_minimum_msat = {
+                                               let curr_htlc_min = cmp::max(
+                                                       candidate.htlc_minimum_msat(), aggregate_next_hops_path_htlc_minimum_msat
+                                               );
+                                               let curr_htlc_min_fee = if let Some(val) = compute_fees(curr_htlc_min, hop.fees) { val } else { break };
+                                               if let Some(min) = curr_htlc_min.checked_add(curr_htlc_min_fee) { min } else { break }
+                                       };
 
                                        if idx == route.0.len() - 1 {
                                                // The last hop in this iterator is the first hop in
@@ -2320,8 +2343,8 @@ where L::Target: Logger {
                                // recompute the fees again, so that if that's the case, we match the currently
                                // underpaid htlc_minimum_msat with fees.
                                debug_assert_eq!(payment_path.get_value_msat(), value_contribution_msat);
-                               value_contribution_msat = cmp::min(value_contribution_msat, final_value_msat);
-                               payment_path.update_value_and_recompute_fees(value_contribution_msat);
+                               let desired_value_contribution = cmp::min(value_contribution_msat, final_value_msat);
+                               value_contribution_msat = payment_path.update_value_and_recompute_fees(desired_value_contribution);
 
                                // Since a path allows to transfer as much value as
                                // the smallest channel it has ("bottleneck"), we should recompute
@@ -2884,7 +2907,7 @@ mod tests {
                        Arc::clone(&logger), &scorer, &Default::default(), &random_seed_bytes) {
                                assert_eq!(err, "First hop cannot have our_node_pubkey as a destination.");
                } else { panic!(); }
+
                let route = get_route(&our_id, &route_params, &network_graph.read_only(), None,
                        Arc::clone(&logger), &scorer, &Default::default(), &random_seed_bytes).unwrap();
                assert_eq!(route.paths[0].hops.len(), 2);
@@ -7166,6 +7189,412 @@ mod tests {
                assert_eq!(route.get_total_fees(), blinded_payinfo.fee_base_msat as u64);
                assert_eq!(route.get_total_amount(), amt_msat);
        }
+
+       #[test]
+       fn we_are_intro_node_candidate_hops() {
+               // This previously led to a panic in the router because we'd generate a Path with only a
+               // BlindedTail and 0 unblinded hops, due to the only candidate hops being blinded route hints
+               // where the origin node is the intro node. We now fully disallow considering candidate hops
+               // where the origin node is the intro node.
+               let (secp_ctx, network_graph, _, _, logger) = build_graph();
+               let (_, our_id, _, nodes) = get_nodes(&secp_ctx);
+               let scorer = ln_test_utils::TestScorer::new();
+               let keys_manager = ln_test_utils::TestKeysInterface::new(&[0u8; 32], Network::Testnet);
+               let random_seed_bytes = keys_manager.get_secure_random_bytes();
+               let config = UserConfig::default();
+
+               // Values are taken from the fuzz input that uncovered this panic.
+               let amt_msat = 21_7020_5185_1423_0019;
+
+               let blinded_path = BlindedPath {
+                       introduction_node_id: our_id,
+                       blinding_point: ln_test_utils::pubkey(42),
+                       blinded_hops: vec![
+                               BlindedHop { blinded_node_id: ln_test_utils::pubkey(42 as u8), encrypted_payload: Vec::new() },
+                               BlindedHop { blinded_node_id: ln_test_utils::pubkey(42 as u8), encrypted_payload: Vec::new() }
+                       ],
+               };
+               let blinded_payinfo = BlindedPayInfo {
+                       fee_base_msat: 5052_9027,
+                       fee_proportional_millionths: 0,
+                       htlc_minimum_msat: 21_7020_5185_1423_0019,
+                       htlc_maximum_msat: 1844_6744_0737_0955_1615,
+                       cltv_expiry_delta: 0,
+                       features: BlindedHopFeatures::empty(),
+               };
+               let mut blinded_hints = vec![
+                       (blinded_payinfo.clone(), blinded_path.clone()),
+                       (blinded_payinfo.clone(), blinded_path.clone()),
+               ];
+               blinded_hints[1].1.introduction_node_id = nodes[6];
+
+               let bolt12_features: Bolt12InvoiceFeatures = channelmanager::provided_invoice_features(&config).to_context();
+               let payment_params = PaymentParameters::blinded(blinded_hints.clone())
+                       .with_bolt12_features(bolt12_features.clone()).unwrap();
+
+               let netgraph = network_graph.read_only();
+               let route_params = RouteParameters::from_payment_params_and_value(
+                       payment_params, amt_msat);
+               if let Err(LightningError { err, .. }) = get_route(
+                       &our_id, &route_params, &netgraph, None, Arc::clone(&logger), &scorer, &(), &random_seed_bytes
+               ) {
+                       assert_eq!(err, "Failed to find a path to the given destination");
+               } else { panic!() }
+       }
+
+       #[test]
+       fn we_are_intro_node_bp_in_final_path_fee_calc() {
+               // This previously led to a debug panic in the router because we'd find an invalid Path with
+               // 0 unblinded hops and a blinded tail, leading to the generation of a final
+               // PaymentPathHop::fee_msat that included both the blinded path fees and the final value of
+               // the payment, when it was intended to only include the final value of the payment.
+               let (secp_ctx, network_graph, _, _, logger) = build_graph();
+               let (_, our_id, _, nodes) = get_nodes(&secp_ctx);
+               let scorer = ln_test_utils::TestScorer::new();
+               let keys_manager = ln_test_utils::TestKeysInterface::new(&[0u8; 32], Network::Testnet);
+               let random_seed_bytes = keys_manager.get_secure_random_bytes();
+               let config = UserConfig::default();
+
+               // Values are taken from the fuzz input that uncovered this panic.
+               let amt_msat = 21_7020_5185_1423_0019;
+
+               let blinded_path = BlindedPath {
+                       introduction_node_id: our_id,
+                       blinding_point: ln_test_utils::pubkey(42),
+                       blinded_hops: vec![
+                               BlindedHop { blinded_node_id: ln_test_utils::pubkey(42 as u8), encrypted_payload: Vec::new() },
+                               BlindedHop { blinded_node_id: ln_test_utils::pubkey(42 as u8), encrypted_payload: Vec::new() }
+                       ],
+               };
+               let blinded_payinfo = BlindedPayInfo {
+                       fee_base_msat: 10_4425_1395,
+                       fee_proportional_millionths: 0,
+                       htlc_minimum_msat: 21_7301_9934_9094_0931,
+                       htlc_maximum_msat: 1844_6744_0737_0955_1615,
+                       cltv_expiry_delta: 0,
+                       features: BlindedHopFeatures::empty(),
+               };
+               let mut blinded_hints = vec![
+                       (blinded_payinfo.clone(), blinded_path.clone()),
+                       (blinded_payinfo.clone(), blinded_path.clone()),
+                       (blinded_payinfo.clone(), blinded_path.clone()),
+               ];
+               blinded_hints[1].0.fee_base_msat = 5052_9027;
+               blinded_hints[1].0.htlc_minimum_msat = 21_7020_5185_1423_0019;
+               blinded_hints[1].0.htlc_maximum_msat = 1844_6744_0737_0955_1615;
+
+               blinded_hints[2].1.introduction_node_id = nodes[6];
+
+               let bolt12_features: Bolt12InvoiceFeatures = channelmanager::provided_invoice_features(&config).to_context();
+               let payment_params = PaymentParameters::blinded(blinded_hints.clone())
+                       .with_bolt12_features(bolt12_features.clone()).unwrap();
+
+               let netgraph = network_graph.read_only();
+               let route_params = RouteParameters::from_payment_params_and_value(
+                       payment_params, amt_msat);
+               if let Err(LightningError { err, .. }) = get_route(
+                       &our_id, &route_params, &netgraph, None, Arc::clone(&logger), &scorer, &(), &random_seed_bytes
+               ) {
+                       assert_eq!(err, "Failed to find a path to the given destination");
+               } else { panic!() }
+       }
+
+       #[test]
+       fn min_htlc_overpay_violates_max_htlc() {
+               do_min_htlc_overpay_violates_max_htlc(true);
+               do_min_htlc_overpay_violates_max_htlc(false);
+       }
+       fn do_min_htlc_overpay_violates_max_htlc(blinded_payee: bool) {
+               // Test that if overpaying to meet a later hop's min_htlc and causes us to violate an earlier
+               // hop's max_htlc, we don't consider that candidate hop valid. Previously we would add this hop
+               // to `targets` and build an invalid path with it, and subsquently hit a debug panic asserting
+               // that the used liquidity for a hop was less than its available liquidity limit.
+               let secp_ctx = Secp256k1::new();
+               let logger = Arc::new(ln_test_utils::TestLogger::new());
+               let network_graph = Arc::new(NetworkGraph::new(Network::Testnet, Arc::clone(&logger)));
+               let scorer = ln_test_utils::TestScorer::new();
+               let keys_manager = ln_test_utils::TestKeysInterface::new(&[0u8; 32], Network::Testnet);
+               let random_seed_bytes = keys_manager.get_secure_random_bytes();
+               let config = UserConfig::default();
+
+               // Values are taken from the fuzz input that uncovered this panic.
+               let amt_msat = 7_4009_8048;
+               let (_, our_id, _, nodes) = get_nodes(&secp_ctx);
+               let first_hop_outbound_capacity = 2_7345_2000;
+               let first_hops = vec![get_channel_details(
+                       Some(200), nodes[0], channelmanager::provided_init_features(&config),
+                       first_hop_outbound_capacity
+               )];
+
+               let base_fee = 1_6778_3453;
+               let htlc_min = 2_5165_8240;
+               let payment_params = if blinded_payee {
+                       let blinded_path = BlindedPath {
+                               introduction_node_id: nodes[0],
+                               blinding_point: ln_test_utils::pubkey(42),
+                               blinded_hops: vec![
+                                       BlindedHop { blinded_node_id: ln_test_utils::pubkey(42 as u8), encrypted_payload: Vec::new() },
+                                       BlindedHop { blinded_node_id: ln_test_utils::pubkey(42 as u8), encrypted_payload: Vec::new() }
+                               ],
+                       };
+                       let blinded_payinfo = BlindedPayInfo {
+                               fee_base_msat: base_fee,
+                               fee_proportional_millionths: 0,
+                               htlc_minimum_msat: htlc_min,
+                               htlc_maximum_msat: htlc_min * 1000,
+                               cltv_expiry_delta: 0,
+                               features: BlindedHopFeatures::empty(),
+                       };
+                       let bolt12_features: Bolt12InvoiceFeatures = channelmanager::provided_invoice_features(&config).to_context();
+                       PaymentParameters::blinded(vec![(blinded_payinfo, blinded_path)])
+                               .with_bolt12_features(bolt12_features.clone()).unwrap()
+               } else {
+                       let route_hint = RouteHint(vec![RouteHintHop {
+                               src_node_id: nodes[0],
+                               short_channel_id: 42,
+                               fees: RoutingFees {
+                                       base_msat: base_fee,
+                                       proportional_millionths: 0,
+                               },
+                               cltv_expiry_delta: 10,
+                               htlc_minimum_msat: Some(htlc_min),
+                               htlc_maximum_msat: None,
+                       }]);
+
+                       PaymentParameters::from_node_id(nodes[1], 42)
+                               .with_route_hints(vec![route_hint]).unwrap()
+                               .with_bolt11_features(channelmanager::provided_invoice_features(&config)).unwrap()
+               };
+
+               let netgraph = network_graph.read_only();
+               let route_params = RouteParameters::from_payment_params_and_value(
+                       payment_params, amt_msat);
+               if let Err(LightningError { err, .. }) = get_route(
+                       &our_id, &route_params, &netgraph, Some(&first_hops.iter().collect::<Vec<_>>()),
+                       Arc::clone(&logger), &scorer, &(), &random_seed_bytes
+               ) {
+                       assert_eq!(err, "Failed to find a path to the given destination");
+               } else { panic!() }
+       }
+
+       #[test]
+       fn previously_used_liquidity_violates_max_htlc() {
+               do_previously_used_liquidity_violates_max_htlc(true);
+               do_previously_used_liquidity_violates_max_htlc(false);
+
+       }
+       fn do_previously_used_liquidity_violates_max_htlc(blinded_payee: bool) {
+               // Test that if a candidate first_hop<>route_hint_src_node channel does not have enough
+               // contribution amount to cover the next hop's min_htlc plus fees, we will not consider that
+               // candidate. In this case, the candidate does not have enough due to a previous path taking up
+               // some of its liquidity. Previously we would construct an invalid path and hit a debug panic
+               // asserting that the used liquidity for a hop was less than its available liquidity limit.
+               let secp_ctx = Secp256k1::new();
+               let logger = Arc::new(ln_test_utils::TestLogger::new());
+               let network_graph = Arc::new(NetworkGraph::new(Network::Testnet, Arc::clone(&logger)));
+               let scorer = ln_test_utils::TestScorer::new();
+               let keys_manager = ln_test_utils::TestKeysInterface::new(&[0u8; 32], Network::Testnet);
+               let random_seed_bytes = keys_manager.get_secure_random_bytes();
+               let config = UserConfig::default();
+
+               // Values are taken from the fuzz input that uncovered this panic.
+               let amt_msat = 52_4288;
+               let (_, our_id, _, nodes) = get_nodes(&secp_ctx);
+               let first_hops = vec![get_channel_details(
+                       Some(161), nodes[0], channelmanager::provided_init_features(&config), 486_4000
+               ), get_channel_details(
+                       Some(122), nodes[0], channelmanager::provided_init_features(&config), 179_5000
+               )];
+
+               let base_fees = [0, 425_9840, 0, 0];
+               let htlc_mins = [1_4392, 19_7401, 1027, 6_5535];
+               let payment_params = if blinded_payee {
+                       let blinded_path = BlindedPath {
+                               introduction_node_id: nodes[0],
+                               blinding_point: ln_test_utils::pubkey(42),
+                               blinded_hops: vec![
+                                       BlindedHop { blinded_node_id: ln_test_utils::pubkey(42 as u8), encrypted_payload: Vec::new() },
+                                       BlindedHop { blinded_node_id: ln_test_utils::pubkey(42 as u8), encrypted_payload: Vec::new() }
+                               ],
+                       };
+                       let mut blinded_hints = Vec::new();
+                       for (base_fee, htlc_min) in base_fees.iter().zip(htlc_mins.iter()) {
+                               blinded_hints.push((BlindedPayInfo {
+                                       fee_base_msat: *base_fee,
+                                       fee_proportional_millionths: 0,
+                                       htlc_minimum_msat: *htlc_min,
+                                       htlc_maximum_msat: htlc_min * 100,
+                                       cltv_expiry_delta: 10,
+                                       features: BlindedHopFeatures::empty(),
+                               }, blinded_path.clone()));
+                       }
+                       let bolt12_features: Bolt12InvoiceFeatures = channelmanager::provided_invoice_features(&config).to_context();
+                       PaymentParameters::blinded(blinded_hints.clone())
+                               .with_bolt12_features(bolt12_features.clone()).unwrap()
+               } else {
+                       let mut route_hints = Vec::new();
+                       for (idx, (base_fee, htlc_min)) in base_fees.iter().zip(htlc_mins.iter()).enumerate() {
+                               route_hints.push(RouteHint(vec![RouteHintHop {
+                                       src_node_id: nodes[0],
+                                       short_channel_id: 42 + idx as u64,
+                                       fees: RoutingFees {
+                                               base_msat: *base_fee,
+                                               proportional_millionths: 0,
+                                       },
+                                       cltv_expiry_delta: 10,
+                                       htlc_minimum_msat: Some(*htlc_min),
+                                       htlc_maximum_msat: Some(htlc_min * 100),
+                               }]));
+                       }
+                       PaymentParameters::from_node_id(nodes[1], 42)
+                               .with_route_hints(route_hints).unwrap()
+                               .with_bolt11_features(channelmanager::provided_invoice_features(&config)).unwrap()
+               };
+
+               let netgraph = network_graph.read_only();
+               let route_params = RouteParameters::from_payment_params_and_value(
+                       payment_params, amt_msat);
+
+               let route = get_route(
+                       &our_id, &route_params, &netgraph, Some(&first_hops.iter().collect::<Vec<_>>()),
+                       Arc::clone(&logger), &scorer, &(), &random_seed_bytes
+               ).unwrap();
+               assert_eq!(route.paths.len(), 1);
+               assert_eq!(route.get_total_amount(), amt_msat);
+       }
+
+       #[test]
+       fn candidate_path_min() {
+               // Test that if a candidate first_hop<>network_node channel does not have enough contribution
+               // amount to cover the next channel's min htlc plus fees, we will not consider that candidate.
+               // Previously, we were storing RouteGraphNodes with a path_min that did not include fees, and
+               // would add a connecting first_hop node that did not have enough contribution amount, leading
+               // to a debug panic upon invalid path construction.
+               let secp_ctx = Secp256k1::new();
+               let logger = Arc::new(ln_test_utils::TestLogger::new());
+               let network_graph = Arc::new(NetworkGraph::new(Network::Testnet, Arc::clone(&logger)));
+               let gossip_sync = P2PGossipSync::new(network_graph.clone(), None, logger.clone());
+               let scorer = ProbabilisticScorer::new(ProbabilisticScoringDecayParameters::default(), network_graph.clone(), logger.clone());
+               let keys_manager = ln_test_utils::TestKeysInterface::new(&[0u8; 32], Network::Testnet);
+               let random_seed_bytes = keys_manager.get_secure_random_bytes();
+               let config = UserConfig::default();
+
+               // Values are taken from the fuzz input that uncovered this panic.
+               let amt_msat = 7_4009_8048;
+               let (_, our_id, privkeys, nodes) = get_nodes(&secp_ctx);
+               let first_hops = vec![get_channel_details(
+                       Some(200), nodes[0], channelmanager::provided_init_features(&config), 2_7345_2000
+               )];
+
+               add_channel(&gossip_sync, &secp_ctx, &privkeys[0], &privkeys[6], ChannelFeatures::from_le_bytes(id_to_feature_flags(6)), 6);
+               update_channel(&gossip_sync, &secp_ctx, &privkeys[0], UnsignedChannelUpdate {
+                       chain_hash: genesis_block(Network::Testnet).header.block_hash(),
+                       short_channel_id: 6,
+                       timestamp: 1,
+                       flags: 0,
+                       cltv_expiry_delta: (6 << 4) | 0,
+                       htlc_minimum_msat: 0,
+                       htlc_maximum_msat: MAX_VALUE_MSAT,
+                       fee_base_msat: 0,
+                       fee_proportional_millionths: 0,
+                       excess_data: Vec::new()
+               });
+               add_or_update_node(&gossip_sync, &secp_ctx, &privkeys[0], NodeFeatures::from_le_bytes(id_to_feature_flags(1)), 0);
+
+               let htlc_min = 2_5165_8240;
+               let blinded_hints = vec![
+                       (BlindedPayInfo {
+                               fee_base_msat: 1_6778_3453,
+                               fee_proportional_millionths: 0,
+                               htlc_minimum_msat: htlc_min,
+                               htlc_maximum_msat: htlc_min * 100,
+                               cltv_expiry_delta: 10,
+                               features: BlindedHopFeatures::empty(),
+                       }, BlindedPath {
+                               introduction_node_id: nodes[0],
+                               blinding_point: ln_test_utils::pubkey(42),
+                               blinded_hops: vec![
+                                       BlindedHop { blinded_node_id: ln_test_utils::pubkey(42 as u8), encrypted_payload: Vec::new() },
+                                       BlindedHop { blinded_node_id: ln_test_utils::pubkey(42 as u8), encrypted_payload: Vec::new() }
+                               ],
+                       })
+               ];
+               let bolt12_features: Bolt12InvoiceFeatures = channelmanager::provided_invoice_features(&config).to_context();
+               let payment_params = PaymentParameters::blinded(blinded_hints.clone())
+                       .with_bolt12_features(bolt12_features.clone()).unwrap();
+               let route_params = RouteParameters::from_payment_params_and_value(
+                       payment_params, amt_msat);
+               let netgraph = network_graph.read_only();
+
+               if let Err(LightningError { err, .. }) = get_route(
+                       &our_id, &route_params, &netgraph, Some(&first_hops.iter().collect::<Vec<_>>()),
+                       Arc::clone(&logger), &scorer, &ProbabilisticScoringFeeParameters::default(),
+                       &random_seed_bytes
+               ) {
+                       assert_eq!(err, "Failed to find a path to the given destination");
+               } else { panic!() }
+       }
+
+       #[test]
+       fn path_contribution_includes_min_htlc_overpay() {
+               // Previously, the fuzzer hit a debug panic because we wouldn't include the amount overpaid to
+               // meet a last hop's min_htlc in the total collected paths value. We now include this value and
+               // also penalize hops along the overpaying path to ensure that it gets deprioritized in path
+               // selection, both tested here.
+               let secp_ctx = Secp256k1::new();
+               let logger = Arc::new(ln_test_utils::TestLogger::new());
+               let network_graph = Arc::new(NetworkGraph::new(Network::Testnet, Arc::clone(&logger)));
+               let scorer = ProbabilisticScorer::new(ProbabilisticScoringDecayParameters::default(), network_graph.clone(), logger.clone());
+               let keys_manager = ln_test_utils::TestKeysInterface::new(&[0u8; 32], Network::Testnet);
+               let random_seed_bytes = keys_manager.get_secure_random_bytes();
+               let config = UserConfig::default();
+
+               // Values are taken from the fuzz input that uncovered this panic.
+               let amt_msat = 562_0000;
+               let (_, our_id, _, nodes) = get_nodes(&secp_ctx);
+               let first_hops = vec![
+                       get_channel_details(
+                               Some(83), nodes[0], channelmanager::provided_init_features(&config), 2199_0000,
+                       ),
+               ];
+
+               let htlc_mins = [49_0000, 1125_0000];
+               let payment_params = {
+                       let blinded_path = BlindedPath {
+                               introduction_node_id: nodes[0],
+                               blinding_point: ln_test_utils::pubkey(42),
+                               blinded_hops: vec![
+                                       BlindedHop { blinded_node_id: ln_test_utils::pubkey(42 as u8), encrypted_payload: Vec::new() },
+                                       BlindedHop { blinded_node_id: ln_test_utils::pubkey(42 as u8), encrypted_payload: Vec::new() }
+                               ],
+                       };
+                       let mut blinded_hints = Vec::new();
+                       for htlc_min in htlc_mins.iter() {
+                               blinded_hints.push((BlindedPayInfo {
+                                       fee_base_msat: 0,
+                                       fee_proportional_millionths: 0,
+                                       htlc_minimum_msat: *htlc_min,
+                                       htlc_maximum_msat: *htlc_min * 100,
+                                       cltv_expiry_delta: 10,
+                                       features: BlindedHopFeatures::empty(),
+                               }, blinded_path.clone()));
+                       }
+                       let bolt12_features: Bolt12InvoiceFeatures = channelmanager::provided_invoice_features(&config).to_context();
+                       PaymentParameters::blinded(blinded_hints.clone())
+                               .with_bolt12_features(bolt12_features.clone()).unwrap()
+               };
+
+               let netgraph = network_graph.read_only();
+               let route_params = RouteParameters::from_payment_params_and_value(
+                       payment_params, amt_msat);
+               let route = get_route(
+                       &our_id, &route_params, &netgraph, Some(&first_hops.iter().collect::<Vec<_>>()),
+                       Arc::clone(&logger), &scorer, &ProbabilisticScoringFeeParameters::default(),
+                       &random_seed_bytes
+               ).unwrap();
+               assert_eq!(route.paths.len(), 1);
+               assert_eq!(route.get_total_amount(), amt_msat);
+       }
 }
 
 #[cfg(all(any(test, ldk_bench), not(feature = "no-std")))]