Refinancing in the same pool requires it to have a higher balance than needed because of a flawed check
Summary
Refinancing a loan into the same pool it is in requires the pool to have the original loan amount +- the difference because it doesn't check whether the pool already has the original amount as outstanding debt.
Vulnerability Details
Lender.sol's refinance() has a check, which makes sure the pool we are refinancing into has enough liquidity to cover the new debt of the loan.
The issue arises when the loan is getting refinanced in the same pool it is already in. Then it will require the pool to have the amount of the loan again instead of just the difference between the old debt and the new debt. This makes it harder for a loan to be refinanced in the same pool as the pool may not have enough liquidity to pass this check.
Impact
Some loans will not be able to be properly refinanced.
Tools Used
Manual Review
Recommendations
Consider checking whether the loan's old pool is the new pool as well first and doing additional checks accordingly.
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