From 10cfe5c973e61251f6bf2180d1fc8d57d5e56ca5 Mon Sep 17 00:00:00 2001 From: Jeffrey Czyz Date: Thu, 5 Jan 2023 11:50:24 -0600 Subject: [PATCH] Fix scorer panic when available capacity is zero ProbabilisticScorer takes a ChannelUsage when computing a penalty for a channel. The formula for calculating the liquidity penalty reduces the maximum capacity by the amount of in-flight HTLCs (available capacity) and adds one to prevent division by zero. However, since the available capacity is passed to DirectedChannelLiquidity as the capacity, other penalty formulas may use the available (i.e., reduced) capacity inadvertently. In practice, this has two ramifications for the historical liquidity penalty computation: 1. The bucket formula doesn't have a consistent denominator for a given channel. 2. The bucket formula may divide by zero when the in-flight HTLC amount equals or exceeds the effective capacity. Fixing this involves only using the available capacity when appropriate. --- lightning/src/routing/scoring.rs | 115 +++++++++++++++++++------------ 1 file changed, 71 insertions(+), 44 deletions(-) diff --git a/lightning/src/routing/scoring.rs b/lightning/src/routing/scoring.rs index 31158d41b..d1ed0f7cb 100644 --- a/lightning/src/routing/scoring.rs +++ b/lightning/src/routing/scoring.rs @@ -702,6 +702,7 @@ struct DirectedChannelLiquidity<'a, L: Deref, BRT: Deref>, L: Deref, T: Time> ProbabilisticScorerU let log_direction = |source, target| { if let Some((directed_info, _)) = chan_debug.as_directed_to(target) { let amt = directed_info.effective_capacity().as_msat(); - let dir_liq = liq.as_directed(source, target, amt, &self.params); + let dir_liq = liq.as_directed(source, target, 0, amt, &self.params); let buckets = HistoricalMinMaxBuckets { min_liquidity_offset_history: &dir_liq.min_liquidity_offset_history, @@ -781,7 +782,7 @@ impl>, L: Deref, T: Time> ProbabilisticScorerU if let Some(liq) = self.channel_liquidities.get(&scid) { if let Some((directed_info, source)) = chan.as_directed_to(target) { let amt = directed_info.effective_capacity().as_msat(); - let dir_liq = liq.as_directed(source, target, amt, &self.params); + let dir_liq = liq.as_directed(source, target, 0, amt, &self.params); return Some((dir_liq.min_liquidity_msat(), dir_liq.max_liquidity_msat())); } } @@ -818,7 +819,7 @@ impl>, L: Deref, T: Time> ProbabilisticScorerU if let Some(liq) = self.channel_liquidities.get(&scid) { if let Some((directed_info, source)) = chan.as_directed_to(target) { let amt = directed_info.effective_capacity().as_msat(); - let dir_liq = liq.as_directed(source, target, amt, &self.params); + let dir_liq = liq.as_directed(source, target, 0, amt, &self.params); let buckets = HistoricalMinMaxBuckets { min_liquidity_offset_history: &dir_liq.min_liquidity_offset_history, @@ -923,7 +924,8 @@ impl ChannelLiquidity { /// Returns a view of the channel liquidity directed from `source` to `target` assuming /// `capacity_msat`. fn as_directed<'a>( - &self, source: &NodeId, target: &NodeId, capacity_msat: u64, params: &'a ProbabilisticScoringParameters + &self, source: &NodeId, target: &NodeId, inflight_htlc_msat: u64, capacity_msat: u64, + params: &'a ProbabilisticScoringParameters ) -> DirectedChannelLiquidity<'a, &u64, &HistoricalBucketRangeTracker, T, &T> { let (min_liquidity_offset_msat, max_liquidity_offset_msat, min_liquidity_offset_history, max_liquidity_offset_history) = if source < target { @@ -939,6 +941,7 @@ impl ChannelLiquidity { max_liquidity_offset_msat, min_liquidity_offset_history, max_liquidity_offset_history, + inflight_htlc_msat, capacity_msat, last_updated: &self.last_updated, now: T::now(), @@ -949,7 +952,8 @@ impl ChannelLiquidity { /// Returns a mutable view of the channel liquidity directed from `source` to `target` assuming /// `capacity_msat`. fn as_directed_mut<'a>( - &mut self, source: &NodeId, target: &NodeId, capacity_msat: u64, params: &'a ProbabilisticScoringParameters + &mut self, source: &NodeId, target: &NodeId, inflight_htlc_msat: u64, capacity_msat: u64, + params: &'a ProbabilisticScoringParameters ) -> DirectedChannelLiquidity<'a, &mut u64, &mut HistoricalBucketRangeTracker, T, &mut T> { let (min_liquidity_offset_msat, max_liquidity_offset_msat, min_liquidity_offset_history, max_liquidity_offset_history) = if source < target { @@ -965,6 +969,7 @@ impl ChannelLiquidity { max_liquidity_offset_msat, min_liquidity_offset_history, max_liquidity_offset_history, + inflight_htlc_msat, capacity_msat, last_updated: &mut self.last_updated, now: T::now(), @@ -1022,7 +1027,16 @@ impl, BRT: Deref, if params.historical_liquidity_penalty_multiplier_msat != 0 || params.historical_liquidity_penalty_amount_multiplier_msat != 0 { - let payment_amt_64th_bucket = amount_msat * 64 / self.capacity_msat; + let payment_amt_64th_bucket = if amount_msat < u64::max_value() / 64 { + amount_msat * 64 / self.capacity_msat + } 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)) + .try_into().unwrap_or(65) + }; + #[cfg(not(fuzzing))] debug_assert!(payment_amt_64th_bucket <= 64); if payment_amt_64th_bucket > 64 { return res; } @@ -1042,13 +1056,14 @@ impl, BRT: Deref, // If we don't have any valid points (or, once decayed, we have less than a full // point), redo the non-historical calculation with no liquidity bounds tracked and // the historical penalty multipliers. - let max_capacity = self.capacity_msat.saturating_sub(amount_msat).saturating_add(1); + let available_capacity = self.available_capacity(); + let numerator = available_capacity.saturating_sub(amount_msat).saturating_add(1); + let denominator = available_capacity.saturating_add(1); let negative_log10_times_2048 = - approx::negative_log10_times_2048(max_capacity, self.capacity_msat.saturating_add(1)); + approx::negative_log10_times_2048(numerator, denominator); res = res.saturating_add(Self::combined_penalty_msat(amount_msat, negative_log10_times_2048, params.historical_liquidity_penalty_multiplier_msat, params.historical_liquidity_penalty_amount_multiplier_msat)); - return res; } } @@ -1080,9 +1095,13 @@ impl, BRT: Deref, /// Returns the upper bound of the channel liquidity balance in this direction. fn max_liquidity_msat(&self) -> u64 { - self.capacity_msat - .checked_sub(self.decayed_offset_msat(*self.max_liquidity_offset_msat)) - .unwrap_or(0) + self.available_capacity() + .saturating_sub(self.decayed_offset_msat(*self.max_liquidity_offset_msat)) + } + + /// Returns the capacity minus the in-flight HTLCs in this direction. + fn available_capacity(&self) -> u64 { + self.capacity_msat.saturating_sub(self.inflight_htlc_msat) } fn decayed_offset_msat(&self, offset_msat: u64) -> u64 { @@ -1201,12 +1220,12 @@ impl>, L: Deref, T: Time> Score for Probabilis } let amount_msat = usage.amount_msat; - let capacity_msat = usage.effective_capacity.as_msat() - .saturating_sub(usage.inflight_htlc_msat); + let capacity_msat = usage.effective_capacity.as_msat(); + let inflight_htlc_msat = usage.inflight_htlc_msat; self.channel_liquidities .get(&short_channel_id) .unwrap_or(&ChannelLiquidity::new()) - .as_directed(source, target, capacity_msat, &self.params) + .as_directed(source, target, inflight_htlc_msat, capacity_msat, &self.params) .penalty_msat(amount_msat, &self.params) .saturating_add(anti_probing_penalty_msat) .saturating_add(base_penalty_msat) @@ -1234,13 +1253,13 @@ impl>, L: Deref, T: Time> Score for Probabilis self.channel_liquidities .entry(hop.short_channel_id) .or_insert_with(ChannelLiquidity::new) - .as_directed_mut(source, &target, capacity_msat, &self.params) + .as_directed_mut(source, &target, 0, capacity_msat, &self.params) .failed_at_channel(amount_msat, format_args!("SCID {}, towards {:?}", hop.short_channel_id, target), &self.logger); } else { self.channel_liquidities .entry(hop.short_channel_id) .or_insert_with(ChannelLiquidity::new) - .as_directed_mut(source, &target, capacity_msat, &self.params) + .as_directed_mut(source, &target, 0, capacity_msat, &self.params) .failed_downstream(amount_msat, format_args!("SCID {}, towards {:?}", hop.short_channel_id, target), &self.logger); } } else { @@ -1268,7 +1287,7 @@ impl>, L: Deref, T: Time> Score for Probabilis self.channel_liquidities .entry(hop.short_channel_id) .or_insert_with(ChannelLiquidity::new) - .as_directed_mut(source, &target, capacity_msat, &self.params) + .as_directed_mut(source, &target, 0, capacity_msat, &self.params) .successful(amount_msat, format_args!("SCID {}, towards {:?}", hop.short_channel_id, target), &self.logger); } else { log_debug!(self.logger, "Not able to learn for channel with SCID {} as we do not have graph info for it (likely a route-hint last-hop).", @@ -1873,52 +1892,52 @@ mod tests { // Update minimum liquidity. let liquidity = scorer.channel_liquidities.get(&42).unwrap() - .as_directed(&source, &target, 1_000, &scorer.params); + .as_directed(&source, &target, 0, 1_000, &scorer.params); assert_eq!(liquidity.min_liquidity_msat(), 100); assert_eq!(liquidity.max_liquidity_msat(), 300); let liquidity = scorer.channel_liquidities.get(&42).unwrap() - .as_directed(&target, &source, 1_000, &scorer.params); + .as_directed(&target, &source, 0, 1_000, &scorer.params); assert_eq!(liquidity.min_liquidity_msat(), 700); assert_eq!(liquidity.max_liquidity_msat(), 900); scorer.channel_liquidities.get_mut(&42).unwrap() - .as_directed_mut(&source, &target, 1_000, &scorer.params) + .as_directed_mut(&source, &target, 0, 1_000, &scorer.params) .set_min_liquidity_msat(200); let liquidity = scorer.channel_liquidities.get(&42).unwrap() - .as_directed(&source, &target, 1_000, &scorer.params); + .as_directed(&source, &target, 0, 1_000, &scorer.params); assert_eq!(liquidity.min_liquidity_msat(), 200); assert_eq!(liquidity.max_liquidity_msat(), 300); let liquidity = scorer.channel_liquidities.get(&42).unwrap() - .as_directed(&target, &source, 1_000, &scorer.params); + .as_directed(&target, &source, 0, 1_000, &scorer.params); assert_eq!(liquidity.min_liquidity_msat(), 700); assert_eq!(liquidity.max_liquidity_msat(), 800); // Update maximum liquidity. let liquidity = scorer.channel_liquidities.get(&43).unwrap() - .as_directed(&target, &recipient, 1_000, &scorer.params); + .as_directed(&target, &recipient, 0, 1_000, &scorer.params); assert_eq!(liquidity.min_liquidity_msat(), 700); assert_eq!(liquidity.max_liquidity_msat(), 900); let liquidity = scorer.channel_liquidities.get(&43).unwrap() - .as_directed(&recipient, &target, 1_000, &scorer.params); + .as_directed(&recipient, &target, 0, 1_000, &scorer.params); assert_eq!(liquidity.min_liquidity_msat(), 100); assert_eq!(liquidity.max_liquidity_msat(), 300); scorer.channel_liquidities.get_mut(&43).unwrap() - .as_directed_mut(&target, &recipient, 1_000, &scorer.params) + .as_directed_mut(&target, &recipient, 0, 1_000, &scorer.params) .set_max_liquidity_msat(200); let liquidity = scorer.channel_liquidities.get(&43).unwrap() - .as_directed(&target, &recipient, 1_000, &scorer.params); + .as_directed(&target, &recipient, 0, 1_000, &scorer.params); assert_eq!(liquidity.min_liquidity_msat(), 0); assert_eq!(liquidity.max_liquidity_msat(), 200); let liquidity = scorer.channel_liquidities.get(&43).unwrap() - .as_directed(&recipient, &target, 1_000, &scorer.params); + .as_directed(&recipient, &target, 0, 1_000, &scorer.params); assert_eq!(liquidity.min_liquidity_msat(), 800); assert_eq!(liquidity.max_liquidity_msat(), 1000); } @@ -1942,42 +1961,42 @@ mod tests { // Check initial bounds. let liquidity = scorer.channel_liquidities.get(&42).unwrap() - .as_directed(&source, &target, 1_000, &scorer.params); + .as_directed(&source, &target, 0, 1_000, &scorer.params); assert_eq!(liquidity.min_liquidity_msat(), 400); assert_eq!(liquidity.max_liquidity_msat(), 800); let liquidity = scorer.channel_liquidities.get(&42).unwrap() - .as_directed(&target, &source, 1_000, &scorer.params); + .as_directed(&target, &source, 0, 1_000, &scorer.params); assert_eq!(liquidity.min_liquidity_msat(), 200); assert_eq!(liquidity.max_liquidity_msat(), 600); // Reset from source to target. scorer.channel_liquidities.get_mut(&42).unwrap() - .as_directed_mut(&source, &target, 1_000, &scorer.params) + .as_directed_mut(&source, &target, 0, 1_000, &scorer.params) .set_min_liquidity_msat(900); let liquidity = scorer.channel_liquidities.get(&42).unwrap() - .as_directed(&source, &target, 1_000, &scorer.params); + .as_directed(&source, &target, 0, 1_000, &scorer.params); assert_eq!(liquidity.min_liquidity_msat(), 900); assert_eq!(liquidity.max_liquidity_msat(), 1_000); let liquidity = scorer.channel_liquidities.get(&42).unwrap() - .as_directed(&target, &source, 1_000, &scorer.params); + .as_directed(&target, &source, 0, 1_000, &scorer.params); assert_eq!(liquidity.min_liquidity_msat(), 0); assert_eq!(liquidity.max_liquidity_msat(), 100); // Reset from target to source. scorer.channel_liquidities.get_mut(&42).unwrap() - .as_directed_mut(&target, &source, 1_000, &scorer.params) + .as_directed_mut(&target, &source, 0, 1_000, &scorer.params) .set_min_liquidity_msat(400); let liquidity = scorer.channel_liquidities.get(&42).unwrap() - .as_directed(&source, &target, 1_000, &scorer.params); + .as_directed(&source, &target, 0, 1_000, &scorer.params); assert_eq!(liquidity.min_liquidity_msat(), 0); assert_eq!(liquidity.max_liquidity_msat(), 600); let liquidity = scorer.channel_liquidities.get(&42).unwrap() - .as_directed(&target, &source, 1_000, &scorer.params); + .as_directed(&target, &source, 0, 1_000, &scorer.params); assert_eq!(liquidity.min_liquidity_msat(), 400); assert_eq!(liquidity.max_liquidity_msat(), 1_000); } @@ -2001,42 +2020,42 @@ mod tests { // Check initial bounds. let liquidity = scorer.channel_liquidities.get(&42).unwrap() - .as_directed(&source, &target, 1_000, &scorer.params); + .as_directed(&source, &target, 0, 1_000, &scorer.params); assert_eq!(liquidity.min_liquidity_msat(), 400); assert_eq!(liquidity.max_liquidity_msat(), 800); let liquidity = scorer.channel_liquidities.get(&42).unwrap() - .as_directed(&target, &source, 1_000, &scorer.params); + .as_directed(&target, &source, 0, 1_000, &scorer.params); assert_eq!(liquidity.min_liquidity_msat(), 200); assert_eq!(liquidity.max_liquidity_msat(), 600); // Reset from source to target. scorer.channel_liquidities.get_mut(&42).unwrap() - .as_directed_mut(&source, &target, 1_000, &scorer.params) + .as_directed_mut(&source, &target, 0, 1_000, &scorer.params) .set_max_liquidity_msat(300); let liquidity = scorer.channel_liquidities.get(&42).unwrap() - .as_directed(&source, &target, 1_000, &scorer.params); + .as_directed(&source, &target, 0, 1_000, &scorer.params); assert_eq!(liquidity.min_liquidity_msat(), 0); assert_eq!(liquidity.max_liquidity_msat(), 300); let liquidity = scorer.channel_liquidities.get(&42).unwrap() - .as_directed(&target, &source, 1_000, &scorer.params); + .as_directed(&target, &source, 0, 1_000, &scorer.params); assert_eq!(liquidity.min_liquidity_msat(), 700); assert_eq!(liquidity.max_liquidity_msat(), 1_000); // Reset from target to source. scorer.channel_liquidities.get_mut(&42).unwrap() - .as_directed_mut(&target, &source, 1_000, &scorer.params) + .as_directed_mut(&target, &source, 0, 1_000, &scorer.params) .set_max_liquidity_msat(600); let liquidity = scorer.channel_liquidities.get(&42).unwrap() - .as_directed(&source, &target, 1_000, &scorer.params); + .as_directed(&source, &target, 0, 1_000, &scorer.params); assert_eq!(liquidity.min_liquidity_msat(), 400); assert_eq!(liquidity.max_liquidity_msat(), 1_000); let liquidity = scorer.channel_liquidities.get(&42).unwrap() - .as_directed(&target, &source, 1_000, &scorer.params); + .as_directed(&target, &source, 0, 1_000, &scorer.params); assert_eq!(liquidity.min_liquidity_msat(), 0); assert_eq!(liquidity.max_liquidity_msat(), 600); } @@ -2774,6 +2793,14 @@ mod tests { // data entirely instead. assert_eq!(scorer.historical_estimated_channel_liquidity_probabilities(42, &target), Some(([0; 8], [0; 8]))); + + let usage = ChannelUsage { + amount_msat: 100, + inflight_htlc_msat: 1024, + effective_capacity: EffectiveCapacity::Total { capacity_msat: 1_024, htlc_maximum_msat: 1_024 }, + }; + scorer.payment_path_failed(&payment_path_for_amount(1).iter().collect::>(), 42); + assert_eq!(scorer.channel_penalty_msat(42, &source, &target, usage), 2048); } #[test] -- 2.39.5