Make `max_total_cltv_expiry_delta` include the final CLTV

This fixes an integer underflow found by the `router` fuzz target
in CI.

diff --git a/lightning/src/ln/functional_tests.rs b/lightning/src/ln/functional_tests.rs
index ead2a8e2f4eccba54d09e9d849b256d40193a20f..5c0f0c87b3c9b652025288b37867a4271abcad6c 100644 (file)
--- a/lightning/src/ln/functional_tests.rs
+++ b/lightning/src/ln/functional_tests.rs
@@ -6493,7 +6493,8 @@ fn test_update_add_htlc_bolt2_sender_cltv_expiry_too_high() {
        let mut nodes = create_network(2, &node_cfgs, &node_chanmgrs);
        let _chan = create_announced_chan_between_nodes_with_value(&nodes, 0, 1, 1000000, 0, InitFeatures::known(), InitFeatures::known());
 
-       let (route, our_payment_hash, _, our_payment_secret) = get_route_and_payment_hash!(nodes[0], nodes[1], vec![], 100000000, 500000001);
+       let (mut route, our_payment_hash, _, our_payment_secret) = get_route_and_payment_hash!(nodes[0], nodes[1], vec![], 100000000, 0);
+       route.paths[0].last_mut().unwrap().cltv_expiry_delta = 500000001;
        unwrap_send_err!(nodes[0].node.send_payment(&route, our_payment_hash, &Some(our_payment_secret)), true, APIError::RouteError { ref err },
                assert_eq!(err, &"Channel CLTV overflowed?"));
 }

diff --git a/lightning/src/routing/router.rs b/lightning/src/routing/router.rs
index 582b6f24491069be1402513d2fa7343e2650c5a7..48960cdecae91947f1f71838157f1ef012998127 100644 (file)
--- a/lightning/src/routing/router.rs
+++ b/lightning/src/routing/router.rs
@@ -670,6 +670,9 @@ where L::Target: Logger {
                        }
                }
        }
+       if payment_params.max_total_cltv_expiry_delta <= final_cltv_expiry_delta {
+               return Err(LightningError{err: "Can't find a route where the maximum total CLTV expiry delta is below the final CLTV expiry.".to_owned(), action: ErrorAction::IgnoreError});
+       }
 
        // The general routing idea is the following:
        // 1. Fill first/last hops communicated by the caller.
@@ -866,9 +869,9 @@ where L::Target: Logger {
                                        // In order to already account for some of the privacy enhancing random CLTV
                                        // expiry delta offset we add on top later, we subtract a rough estimate
                                        // (2*MEDIAN_HOP_CLTV_EXPIRY_DELTA) here.
-                                       let max_total_cltv_expiry_delta = payment_params.max_total_cltv_expiry_delta
+                                       let max_total_cltv_expiry_delta = (payment_params.max_total_cltv_expiry_delta - final_cltv_expiry_delta)
                                                .checked_sub(2*MEDIAN_HOP_CLTV_EXPIRY_DELTA)
-                                               .unwrap_or(payment_params.max_total_cltv_expiry_delta);
+                                               .unwrap_or(payment_params.max_total_cltv_expiry_delta - final_cltv_expiry_delta);
                                        let hop_total_cltv_delta = ($next_hops_cltv_delta as u32)
                                                .checked_add($candidate.cltv_expiry_delta())
                                                .unwrap_or(u32::max_value());
@@ -5091,7 +5094,7 @@ mod tests {
                        .with_max_total_cltv_expiry_delta(feasible_max_total_cltv_delta);
                let keys_manager = test_utils::TestKeysInterface::new(&[0u8; 32], Network::Testnet);
                let random_seed_bytes = keys_manager.get_secure_random_bytes();
-               let route = get_route(&our_id, &feasible_payment_params, &network_graph, None, 100, 42, Arc::clone(&logger), &scorer, &random_seed_bytes).unwrap();
+               let route = get_route(&our_id, &feasible_payment_params, &network_graph, None, 100, 0, Arc::clone(&logger), &scorer, &random_seed_bytes).unwrap();
                let path = route.paths[0].iter().map(|hop| hop.short_channel_id).collect::<Vec<_>>();
                assert_ne!(path.len(), 0);
 
@@ -5099,7 +5102,7 @@ mod tests {
                let fail_max_total_cltv_delta = 23;
                let fail_payment_params = PaymentParameters::from_node_id(nodes[6]).with_route_hints(last_hops(&nodes))
                        .with_max_total_cltv_expiry_delta(fail_max_total_cltv_delta);
-               match get_route(&our_id, &fail_payment_params, &network_graph, None, 100, 42, Arc::clone(&logger), &scorer, &random_seed_bytes)
+               match get_route(&our_id, &fail_payment_params, &network_graph, None, 100, 0, Arc::clone(&logger), &scorer, &random_seed_bytes)
                {
                        Err(LightningError { err, .. } ) => {
                                assert_eq!(err, "Failed to find a path to the given destination");