52837 sc insight gas heavy repeated binary search increases reward calculation gas costs

Submitted on Aug 13th 2025 at 14:44:45 UTC by @Khay3 for Attackathon | Plume Network

• Report ID: #52837

• Report Type: Smart Contract

• Report severity: Insight

• Target: https://github.com/immunefi-team/attackathon-plume-network/blob/main/plume/src/lib/PlumeRewardLogic.sol

Description

Summary

Repeated on-chain binary searches over dynamically growing checkpoint arrays during every reward accrual dramatically inflate gas usage, especially as the number of checkpoints grows.

Vulnerability Detail

PlumeRewardLogic::findRewardRateCheckpointIndexAtOrBefore and PlumeRewardLogic::findCommissionCheckpointIndexAtOrBefore perform an O(log n) search each time calculateRewardsWithCheckpoints() is called. Because reward/commission checkpoints are appended on every rate change and there is no hard cap for reward checkpoints, the arrays can grow unbounded.

Consequently, a single user claim traverses both searches inside nested loops, compounding gas costs linearly with the number of segments processed.

Snippet from plume/src/lib/PlumeRewardLogic.sol:L629-L671:

plume/src/lib/PlumeRewardLogic.sol:L629-L671

while (low <= high) {
    uint256 mid = low + (high - low) / 2;
    if (checkpoints[mid].timestamp <= timestamp) {
        ans = mid;
        low = mid + 1;
    } else {
        if (mid == 0) break;
        high = mid - 1;
    }
}

With dozens of checkpoints per validator (daily reward updates, frequent commission tweaks), claims can approach or exceed block gas limits, making reward settlement unusable.

Impact

Large checkpoint arrays make every reward accrual and claim increasingly expensive. High-volume checkpoint creation can push transactions beyond block gas limits, causing denial-of-service for stakers and administrators.

Recommendation

1

Cache last-used checkpoint index

Cache the last-used checkpoint index per validator/token and reuse it when timestamp moves monotonically forward to avoid repeated binary searches.

2

Limit checkpoint growth / prune

Impose a reasonable upper bound on reward checkpoint length (similar to maxCommissionCheckpoints) or prune old entries off-chain and migrate cumulative indices on-chain.

3

Store cumulative indices for O(1) lookups

Optionally store cumulative indices in mappings keyed by block ranges to enable O(1) look-ups without per-call searches.

Proof of Concept

Proof of Concept

No Proof of Concept provided.