`RToken::transferFrom` makes inaccurate transfers
Summary
This is due to the _liquidityIndex variable
Vulnerability Details
_liquidityIndex is set to 1 RAY in the constructor of RToken. There is the updateLiquidityIndex function , which is ment to update the variable but it is only callable by the LendingPool, leaving the variable equal to 1 RAY practically forever. This makes it impossible for the transferFrom function to perform an accurate transfer, because the amount transferred should be denominated in underlying assets and then scaled by the active liquidity index
Impact
RToken::transferFrom performs inacurate transfers which may be an issue in the StabilityPool contract
Tools Used
Manual Review
Recommendations
fetch the liquidity index from LendingPool instead of relying to the _liquidityIndex variable
Lead Judging Commences
RToken::updateLiquidityIndex() has onlyReservePool modifier but LendingPool never calls it, causing transferFrom() to use stale liquidity index values
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