From bfd1a5743427599500360a86ba72eaf4e03b068d Mon Sep 17 00:00:00 2001 From: Jeffrey Czyz Date: Thu, 5 Jan 2023 22:00:31 -0600 Subject: [PATCH] Guard against division by zero in scorer Since a node may announce that the htlc_maximum_msat of a channel is zero, adding one to the denominator in the bucket formulas will prevent the panic from ever happening. While the routing algorithm may never select such a channel to score, this precaution may still be useful in case the algorithm changes or if the scorer is used with a different routing algorithm. --- lightning/src/routing/scoring.rs | 34 +++++++++++++++++++++++++------- 1 file changed, 27 insertions(+), 7 deletions(-) diff --git a/lightning/src/routing/scoring.rs b/lightning/src/routing/scoring.rs index 4e825ee16..adfc59c92 100644 --- a/lightning/src/routing/scoring.rs +++ b/lightning/src/routing/scoring.rs @@ -575,7 +575,7 @@ impl HistoricalBucketRangeTracker { // Ensure the bucket index is in the range [0, 7], even if the liquidity offset is zero or // the channel's capacity, though the second should generally never happen. debug_assert!(liquidity_offset_msat <= capacity_msat); - let bucket_idx: u8 = (liquidity_offset_msat.saturating_sub(1) * 8 / capacity_msat) + let bucket_idx: u8 = (liquidity_offset_msat * 8 / capacity_msat.saturating_add(1)) .try_into().unwrap_or(32); // 32 is bogus for 8 buckets, and will be ignored debug_assert!(bucket_idx < 8); if bucket_idx < 8 { @@ -1034,12 +1034,12 @@ impl, BRT: Deref, if params.historical_liquidity_penalty_multiplier_msat != 0 || params.historical_liquidity_penalty_amount_multiplier_msat != 0 { let payment_amt_64th_bucket = if amount_msat < u64::max_value() / 64 { - amount_msat * 64 / self.capacity_msat + amount_msat * 64 / self.capacity_msat.saturating_add(1) } else { // Only use 128-bit arithmetic when multiplication will overflow to avoid 128-bit // division. This branch should only be hit in fuzz testing since the amount would // need to be over 2.88 million BTC in practice. - ((amount_msat as u128) * 64 / (self.capacity_msat as u128)) + ((amount_msat as u128) * 64 / (self.capacity_msat as u128).saturating_add(1)) .try_into().unwrap_or(65) }; #[cfg(not(fuzzing))] @@ -1817,13 +1817,13 @@ mod tests { let chain_source: Option<&crate::util::test_utils::TestChainSource> = None; network_graph.update_channel_from_announcement( &signed_announcement, &chain_source).unwrap(); - update_channel(network_graph, short_channel_id, node_1_key, 0); - update_channel(network_graph, short_channel_id, node_2_key, 1); + update_channel(network_graph, short_channel_id, node_1_key, 0, 1_000); + update_channel(network_graph, short_channel_id, node_2_key, 1, 0); } fn update_channel( network_graph: &mut NetworkGraph<&TestLogger>, short_channel_id: u64, node_key: SecretKey, - flags: u8 + flags: u8, htlc_maximum_msat: u64 ) { let genesis_hash = genesis_block(Network::Testnet).header.block_hash(); let secp_ctx = Secp256k1::new(); @@ -1834,7 +1834,7 @@ mod tests { flags, cltv_expiry_delta: 18, htlc_minimum_msat: 0, - htlc_maximum_msat: 1_000, + htlc_maximum_msat, fee_base_msat: 1, fee_proportional_millionths: 0, excess_data: Vec::new(), @@ -2754,6 +2754,7 @@ mod tests { let logger = TestLogger::new(); let network_graph = network_graph(&logger); let params = ProbabilisticScoringParameters { + liquidity_offset_half_life: Duration::from_secs(60 * 60), historical_liquidity_penalty_multiplier_msat: 1024, historical_liquidity_penalty_amount_multiplier_msat: 1024, historical_no_updates_half_life: Duration::from_secs(10), @@ -2804,6 +2805,25 @@ mod tests { }; scorer.payment_path_failed(&payment_path_for_amount(1).iter().collect::>(), 42); assert_eq!(scorer.channel_penalty_msat(42, &source, &target, usage), 409); + + let usage = ChannelUsage { + amount_msat: 1, + inflight_htlc_msat: 0, + effective_capacity: EffectiveCapacity::MaximumHTLC { amount_msat: 0 }, + }; + assert_eq!(scorer.channel_penalty_msat(42, &target, &source, usage), 2048); + + // Advance to decay all liquidity offsets to zero. + SinceEpoch::advance(Duration::from_secs(60 * 60 * 10)); + + // Use a path in the opposite direction, which have zero for htlc_maximum_msat. This will + // ensure that the effective capacity is zero to test division-by-zero edge cases. + let path = vec![ + path_hop(target_pubkey(), 43, 2), + path_hop(source_pubkey(), 42, 1), + path_hop(sender_pubkey(), 41, 0), + ]; + scorer.payment_path_failed(&path.iter().collect::>(), 42); } #[test] -- 2.39.5