Core Contracts

Summary

Vulnerability Details

To found out this Bug, Workflow is like below

• Lp call `LendingPool :: deposit()` with amount

• this function further call ReserveLibrary.deposit()

• after updating Reserves interst updateReserveInterests (liquidityIndex and usagesIndex), minting of `rToken` happens

  function mint(

  address caller,

  address onBehalfOf,

  uint256 amountToMint,

  uint256 index

  ) external override onlyReservePool returns (bool, uint256, uint256, uint256) {

  if (amountToMint == 0) {

  return (false, 0, 0, 0);

  }

  uint256 amountScaled = amountToMint.rayDiv(index);

  if (amountScaled == 0) revert InvalidAmount();

  ​

  uint256 scaledBalance = balanceOf(onBehalfOf);

  bool isFirstMint = scaledBalance == 0;

  ​

  uint256 balanceIncrease = 0;

  if (_userState[onBehalfOf].index != 0 && _userState[onBehalfOf].index < index) {

  balanceIncrease = scaledBalance.rayMul(index) - scaledBalance.rayMul(_userState[onBehalfOf].index);

  }

  ​

  _userState[onBehalfOf].index = index.toUint128();

  ​

  _mint(onBehalfOf, amountToMint.toUint128());

  ​

  emit Mint(caller, onBehalfOf, amountToMint, index);

  ​

  return (isFirstMint, amountToMint, totalSupply(), amountScaled);

  }

here balnaceIncrease is calculated for previously deposited LPs

But as you can see this balanceIncreasevariable never used further in that code base, and _userState[onBehalfOf].indexis updated with current liquidity index,

That means all the Interst accured by Lp from previous liquidity index to current liquidity index will be lost.

https://github.com/Cyfrin/2025-02-raac/blob/main/contracts/core/tokens/RToken.sol#L129-L139

Impact

Lp losing their intest on previous deposited value.

Tools Used

Manual review

Recommendations

Add balanceIncreasedwith `amountToMint` and Mint resultant amount to caller