Unnecessary future deadline value passed to swap functions

[andreiashu]

Description

Treasury.buybackRnbw() uses Uniswap V2 to convert underlying tokens into USDC:

review-xave-lending-market-2021-10/code/contracts/buyback/Treasury.sol

Lines 63 to 69 in 15d777b

	rnbwBought = IUniswapV2Router02(router).swapExactTokensForTokens(
	usdcBalance,
	0,
	path,
	address(this),
	block.timestamp + 60
	)[0];

The deadline argument passed to swapExactTokensForTokens function is 60 blocks into the future. The deadline parameter is useful for frontend and other off-chain software to ensure there's a deadline after which a swap transaction will revert.

In this case, passing just block.timestamp is enough to ensure correct behavior:

Uniswap's swapExactTokensForTokens definition:

    function swapExactTokensForTokens(
        uint amountIn,
        uint amountOutMin,
        address[] calldata path,
        address to,
        uint deadline
    ) external override ensure(deadline) returns (uint[] memory amounts) {

Uniswap ensure modifier:

    modifier ensure(uint deadline) {
        require(deadline >= block.timestamp, 'UniswapV2Router: EXPIRED');
        _;
    }

Recommendation

Instead of block.timestamp + 60 just pass block.timestamp as the deadline argument to swapExactTokensForTokens call.

Notes

A similar change can be made to the originSwap call:

review-xave-lending-market-2021-10/code/contracts/buyback/Treasury.sol

Lines 81 to 88 in 15d777b

	uint256 targetAmount =
	ICurve(curveAddress).originSwap(
	_underlying,
	USDC,
	_underlyingAmount,
	0,
	block.timestamp + 60
	);

The issue here though is that you still need to add +1 to the block.timestamp because of the way the deadline modifier in Curve.sol is defined. Because of this, we leave it to the Xave Finance team the decision change the call to originSwap since there are no (gas) benefits, although it might provide more clarity to the reader:

    modifier deadline(uint256 _deadline) {
        require(block.timestamp < _deadline, "Curve/tx-deadline-passed");
        _;
    }