Dust repayment rounding issues
Summary
Tiny repayments may round to zero, failing to reduce debt effectively in the RAAC protocol.
Vulnerability Details
In the lending logic, scaledAmount = amount.rayDiv(reserve.usageIndex) could round to zero for very small repayment amounts, preventing the debt from being reduced.
Impact
This issue can result in users being unable to repay small amounts of debt, potentially leading to unnecessary liquidations or increased debt burdens.
Tools Used
Manual review
Recommendations
Introduce minimum repayment amounts or debt forgiveness thresholds to handle dust effectively.
Lead Judging Commences
LendingPool::_repay rayDiv scaling causes dust repayments to round to zero, preventing full debt elimination for tiny amounts
The likelihood of super small debts is veeery low. The impact is also very low. I combined these two with the ability to borrow a small amount (but sufficient to not have this problem) then repaying in the next transaction to clear everything, and got to Informational.
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