Merge pull request #4554 from TheBlueMatt/2026-04-feerate-overflows

Use `saturating_mul` when multiplying feerates by the fee spike buf

Author: tnull

lightning/src/ln/channel.rs

@@ -5847,7 +5847,7 @@ impl<SP: SignerProvider> ChannelContext<SP> {
 					1
 				};
 			// Note that the feerate is 0 in zero-fee commitment channels, so this statement is a noop
-			let spiked_feerate = feerate * fee_spike_multiple;
+			let spiked_feerate = feerate.saturating_mul(fee_spike_multiple);
 			let (remote_stats, _remote_htlcs) = self
 				.get_next_remote_commitment_stats(
 					funding,
@@ -13333,7 +13333,8 @@ where
 		let feerate_per_kw = if !funding.get_channel_type().supports_anchors_zero_fee_htlc_tx() {
 			// Similar to HTLC additions, require the funder to have enough funds reserved for
 			// fees such that the feerate can jump without rendering the channel useless.
-			self.context.feerate_per_kw * FEE_SPIKE_BUFFER_FEE_INCREASE_MULTIPLE as u32
+			let spike_mul = FEE_SPIKE_BUFFER_FEE_INCREASE_MULTIPLE as u32;
+			self.context.feerate_per_kw.saturating_mul(spike_mul)
 		} else {
 			self.context.feerate_per_kw
 		};

lightning/src/sign/tx_builder.rs

@@ -336,12 +336,13 @@ fn get_available_balances(
 		if channel_type.supports_anchor_zero_fee_commitments() { 0 } else { 1 };
 
 	// Note that the feerate is 0 in zero-fee commitment channels, so this statement is a noop
-	let spiked_feerate = feerate_per_kw
-		* if is_outbound_from_holder && !channel_type.supports_anchors_zero_fee_htlc_tx() {
+	let spiked_feerate = feerate_per_kw.saturating_mul(
+		if is_outbound_from_holder && !channel_type.supports_anchors_zero_fee_htlc_tx() {
 			crate::ln::channel::FEE_SPIKE_BUFFER_FEE_INCREASE_MULTIPLE as u32
 		} else {
 			1
-		};
+		},
+	);
 
 	let local_nondust_htlc_count = pending_htlcs
 		.iter()