Polish background probing service

Move probing code in builder before the memory leak checker.

Prevent potential overflow due to public channel info fee values.

Account aggregated fee potentially being bigger than constructed porbing
path's max htlc bound.

Author: randomlogin

src/builder.rs

@@ -2249,18 +2249,6 @@ fn build_with_store_internal(
 
 	let pathfinding_scores_sync_url = pathfinding_scores_sync_config.map(|c| c.url.clone());
 
-	#[cfg(cycle_tests)]
-	let mut _leak_checker = crate::LeakChecker(Vec::new());
-	#[cfg(cycle_tests)]
-	{
-		use std::any::Any;
-		use std::sync::Weak;
-
-		_leak_checker.0.push(Arc::downgrade(&channel_manager) as Weak<dyn Any + Send + Sync>);
-		_leak_checker.0.push(Arc::downgrade(&network_graph) as Weak<dyn Any + Send + Sync>);
-		_leak_checker.0.push(Arc::downgrade(&wallet) as Weak<dyn Any + Send + Sync>);
-	}
-
 	let prober = probing_config.map(|probing_cfg| {
 		let strategy: Arc<dyn ProbingStrategy> = match &probing_cfg.kind {
 			ProbingStrategyKind::HighDegree { top_node_count } => {
@@ -2306,6 +2294,18 @@ fn build_with_store_internal(
 		})
 	});
 
+	#[cfg(cycle_tests)]
+	let mut _leak_checker = crate::LeakChecker(Vec::new());
+	#[cfg(cycle_tests)]
+	{
+		use std::any::Any;
+		use std::sync::Weak;
+
+		_leak_checker.0.push(Arc::downgrade(&channel_manager) as Weak<dyn Any + Send + Sync>);
+		_leak_checker.0.push(Arc::downgrade(&network_graph) as Weak<dyn Any + Send + Sync>);
+		_leak_checker.0.push(Arc::downgrade(&wallet) as Weak<dyn Any + Send + Sync>);
+	}
+
 	Ok(Node {
 		runtime,
 		stop_sender,

src/probing.rs

@@ -595,7 +595,7 @@ impl RandomWalkStrategy {
 			// Retrieve the direction-specific update via the public ChannelInfo fields.
 			// as_directed_from already checked both directions are Some, but we break
 			// defensively rather than unwrap.
-			let update = match if directed.source() == &next_channel.node_one {
+			let channel_update_info = match if directed.source() == &next_channel.node_one {
 				next_channel.one_to_two.as_ref()
 			} else {
 				next_channel.two_to_one.as_ref()
@@ -604,15 +604,15 @@ impl RandomWalkStrategy {
 				None => break,
 			};
 
-			if !update.enabled {
+			if !channel_update_info.enabled {
 				break;
 			}
 
 			route_least_htlc_upper_bound =
-				route_least_htlc_upper_bound.min(update.htlc_maximum_msat);
+				route_least_htlc_upper_bound.min(channel_update_info.htlc_maximum_msat);
 
 			route_greatest_htlc_lower_bound =
-				route_greatest_htlc_lower_bound.max(update.htlc_minimum_msat);
+				route_greatest_htlc_lower_bound.max(channel_update_info.htlc_minimum_msat);
 
 			let next_pubkey = match PublicKey::try_from(*next_node_id) {
 				Ok(pk) => pk,
@@ -682,25 +682,36 @@ impl RandomWalkStrategy {
 			let (_, next_scid, _) = route[i + 1];
 			let next_channel = graph.channel(next_scid)?;
 			let (directed, _) = next_channel.as_directed_from(&node_id)?;
-			let update = match if directed.source() == &next_channel.node_one {
+			let channel_update_info = match if directed.source() == &next_channel.node_one {
 				next_channel.one_to_two.as_ref()
 			} else {
 				next_channel.two_to_one.as_ref()
 			} {
 				Some(u) => u,
 				None => return None,
 			};
-			let fee = update.fees.base_msat as u64
-				+ (forwarded * update.fees.proportional_millionths as u64 / 1_000_000);
-			forwarded += fee;
+			// Overflow prevention
+			let proportional_fee = forwarded
+				.checked_mul(channel_update_info.fees.proportional_millionths as u64)
+				.map(|v| v / 1_000_000)?;
+			let fee = (channel_update_info.fees.base_msat as u64).checked_add(proportional_fee)?;
+			forwarded = forwarded.checked_add(fee)?;
+
+			// Fees compound as they're added walking back towards the sender, so re-check the
+			// now-inflated forwarded amount against this channel's own advertised bounds.
+			if forwarded > channel_update_info.htlc_maximum_msat
+				|| forwarded < channel_update_info.htlc_minimum_msat
+			{
+				return None;
+			}
 
 			hops.push(RouteHop {
 				pubkey,
 				node_features,
 				short_channel_id: via_scid,
 				channel_features,
 				fee_msat: fee,
-				cltv_expiry_delta: update.cltv_expiry_delta as u32,
+				cltv_expiry_delta: channel_update_info.cltv_expiry_delta as u32,
 				maybe_announced_channel,
 			});
 		}