Check UpdateAddHTLC::skimmed_fee_msat on receive

[rust-lightning] / lightning / src / ln / channelmanager.rs

diff --git a/lightning/src/ln/channelmanager.rs b/lightning/src/ln/channelmanager.rs
index 9d656d02286f57a5b85b42593b4ac01a397871fd..aef1abe307fd741bf6dd76b8030ae7e001a8284c 100644 (file)
--- a/lightning/src/ln/channelmanager.rs
+++ b/lightning/src/ln/channelmanager.rs
@@ -2528,7 +2528,8 @@ where
 
        fn construct_recv_pending_htlc_info(
                &self, hop_data: msgs::OnionHopData, shared_secret: [u8; 32], payment_hash: PaymentHash,
-               amt_msat: u64, cltv_expiry: u32, phantom_shared_secret: Option<[u8; 32]>, allow_underpay: bool
+               amt_msat: u64, cltv_expiry: u32, phantom_shared_secret: Option<[u8; 32]>, allow_underpay: bool,
+               counterparty_skimmed_fee_msat: Option<u64>,
        ) -> Result<PendingHTLCInfo, ReceiveError> {
                // final_incorrect_cltv_expiry
                if hop_data.outgoing_cltv_value > cltv_expiry {
@@ -2555,7 +2556,10 @@ where
                                msg: "The final CLTV expiry is too soon to handle",
                        });
                }
-               if !allow_underpay && hop_data.amt_to_forward > amt_msat {
+               if (!allow_underpay && hop_data.amt_to_forward > amt_msat) ||
+                       (allow_underpay && hop_data.amt_to_forward >
+                        amt_msat.saturating_add(counterparty_skimmed_fee_msat.unwrap_or(0)))
+               {
                        return Err(ReceiveError {
                                err_code: 19,
                                err_data: amt_msat.to_be_bytes().to_vec(),
@@ -2622,7 +2626,7 @@ where
                        incoming_amt_msat: Some(amt_msat),
                        outgoing_amt_msat: hop_data.amt_to_forward,
                        outgoing_cltv_value: hop_data.outgoing_cltv_value,
-                       skimmed_fee_msat: None,
+                       skimmed_fee_msat: counterparty_skimmed_fee_msat,
                })
        }
 
@@ -2861,7 +2865,7 @@ where
                        onion_utils::Hop::Receive(next_hop_data) => {
                                // OUR PAYMENT!
                                match self.construct_recv_pending_htlc_info(next_hop_data, shared_secret, msg.payment_hash,
-                                       msg.amount_msat, msg.cltv_expiry, None, allow_underpay)
+                                       msg.amount_msat, msg.cltv_expiry, None, allow_underpay, msg.skimmed_fee_msat)
                                {
                                        Ok(info) => {
                                                // Note that we could obviously respond immediately with an update_fulfill_htlc
@@ -3680,7 +3684,7 @@ where
                                                                                                        onion_utils::Hop::Receive(hop_data) => {
                                                                                                                match self.construct_recv_pending_htlc_info(hop_data,
                                                                                                                        incoming_shared_secret, payment_hash, outgoing_amt_msat,
-                                                                                                                       outgoing_cltv_value, Some(phantom_shared_secret), false)
+                                                                                                                       outgoing_cltv_value, Some(phantom_shared_secret), false, None)
                                                                                                                {
                                                                                                                        Ok(info) => phantom_receives.push((prev_short_channel_id, prev_funding_outpoint, prev_user_channel_id, vec![(info, prev_htlc_id)])),
                                                                                                                        Err(ReceiveError { err_code, err_data, msg }) => failed_payment!(msg, err_code, err_data, Some(phantom_shared_secret))
@@ -3931,6 +3935,8 @@ where
                                                                                        htlcs.iter_mut().for_each(|htlc| htlc.total_value_received = Some(amount_msat));
                                                                                        let counterparty_skimmed_fee_msat = htlcs.iter()
                                                                                                .map(|htlc| htlc.counterparty_skimmed_fee_msat.unwrap_or(0)).sum();
+                                                                                       debug_assert!(total_value.saturating_sub(amount_msat) <=
+                                                                                               counterparty_skimmed_fee_msat);
                                                                                        new_events.push_back((events::Event::PaymentClaimable {
                                                                                                receiver_node_id: Some(receiver_node_id),
                                                                                                payment_hash,
@@ -9743,6 +9749,50 @@ mod tests {
                get_event_msg!(nodes[1], MessageSendEvent::SendAcceptChannel, last_random_pk);
        }
 
+       #[test]
+       fn reject_excessively_underpaying_htlcs() {
+               let chanmon_cfg = create_chanmon_cfgs(1);
+               let node_cfg = create_node_cfgs(1, &chanmon_cfg);
+               let node_chanmgr = create_node_chanmgrs(1, &node_cfg, &[None]);
+               let node = create_network(1, &node_cfg, &node_chanmgr);
+               let sender_intended_amt_msat = 100;
+               let extra_fee_msat = 10;
+               let hop_data = msgs::OnionHopData {
+                       amt_to_forward: 100,
+                       outgoing_cltv_value: 42,
+                       format: msgs::OnionHopDataFormat::FinalNode {
+                               keysend_preimage: None,
+                               payment_metadata: None,
+                               payment_data: Some(msgs::FinalOnionHopData {
+                                       payment_secret: PaymentSecret([0; 32]), total_msat: sender_intended_amt_msat,
+                               }),
+                       }
+               };
+               // Check that if the amount we received + the penultimate hop extra fee is less than the sender
+               // intended amount, we fail the payment.
+               if let Err(crate::ln::channelmanager::ReceiveError { err_code, .. }) =
+                       node[0].node.construct_recv_pending_htlc_info(hop_data, [0; 32], PaymentHash([0; 32]),
+                               sender_intended_amt_msat - extra_fee_msat - 1, 42, None, true, Some(extra_fee_msat))
+               {
+                       assert_eq!(err_code, 19);
+               } else { panic!(); }
+
+               // If amt_received + extra_fee is equal to the sender intended amount, we're fine.
+               let hop_data = msgs::OnionHopData { // This is the same hop_data as above, OnionHopData doesn't implement Clone
+                       amt_to_forward: 100,
+                       outgoing_cltv_value: 42,
+                       format: msgs::OnionHopDataFormat::FinalNode {
+                               keysend_preimage: None,
+                               payment_metadata: None,
+                               payment_data: Some(msgs::FinalOnionHopData {
+                                       payment_secret: PaymentSecret([0; 32]), total_msat: sender_intended_amt_msat,
+                               }),
+                       }
+               };
+               assert!(node[0].node.construct_recv_pending_htlc_info(hop_data, [0; 32], PaymentHash([0; 32]),
+                       sender_intended_amt_msat - extra_fee_msat, 42, None, true, Some(extra_fee_msat)).is_ok());
+       }
+
        #[cfg(anchors)]
        #[test]
        fn test_anchors_zero_fee_htlc_tx_fallback() {