Beedle - Oracle free perpetual lending

Summary

Some tokens take a transfer fee (e.g. STA, PAXG), some do not currently charge a fee but may do so in the future (e.g. USDT, USDC).

Vulnerability Details

While transfer of loan token, In the current implementation, it is assumed that the received amount is the same as the transfer amount. However, due to how fee-on-transfer tokens work, much less will be received than what was transferred.

IERC20(p.loanToken).transferFrom(
p.lender,
address(this),
p.poolBalance - currentBalance
);

Impact

The impact of such implementation will be on borrow() since the pool balance will be less than the expected which can lead to failure of borrow()

Tools Used

manual reveiw

Recommendations

In order to obtain the actual amount received by the contract, track the balance of
tokens before and after the transfer of tokens. For example, in the contract test, we recommend
implementing the following steps:

function _transfer(uint256 amount) public returns(uint256){
uint256 balanceBefore = IERC20(token).balanceOf(address(this));
IERC20Token(token).SafetransferFrom(msg.sender, address(this),amount);

   uint256 balanceAfter = IERC20(token).balanceOf(address(this));
   require(balanceAfter >= balanceBefore);
   return balanceAfter - balanceBefore;

}