Add checks that amt_to_forward and outgoing_cltv_value are within

acceptable ranges

Author: Antoine Riard

src/ln/channelmanager.rs

@@ -1625,7 +1625,15 @@ impl ChannelMessageHandler for ChannelManager {
 					hmac: next_hop_data.hmac.clone(),
 				};
 
-				//TODO: Check amt_to_forward and outgoing_cltv_value are within acceptable ranges!
+				let channel_state = self.channel_state.lock().unwrap();
+				let chan = channel_state.by_id.get(&msg.channel_id).unwrap();
+				let fee = chan.get_our_fee_base_msat(&*self.fee_estimator) + (next_hop_data.data.amt_to_forward * self.fee_proportional_millionths as u64 / 1000000) as u32;
+				if msg.amount_msat - fee as u64 >= next_hop_data.data.amt_to_forward {
+					return_err!("Prior hop has deviated from specified parameters", 0x1000 | 12, &[0;0]);
+				}
+				if msg.cltv_expiry - CLTV_EXPIRY_DELTA as u32 >= next_hop_data.data.outgoing_cltv_value {
+					return_err!("Forwarding node has tampered with the intended HTLC values or origin node has an obsolete cltv_expiry_delta", 0x1000 | 13, &[0;0]);
+				}
 
 				PendingForwardHTLCInfo {
 					onion_packet: Some(outgoing_packet),