Handle

Dravee

Vulnerability details

Impact

Increased gas cost due to unnecessary automatic underflow checks.

Solidity version 0.8+ comes with implicit overflow and underflow checks on unsigned integers.

When an overflow or an underflow isn't possible (as an example, when a comparison is made before the arithmetic operation, or the operation doesn't depend on user input), some gas can be saved by using an unchecked block.

https://docs.soliditylang.org/en/v0.8.10/control-structures.html#checked-or-unchecked-arithmetic

Proof of Concept

In ConvexStakingWrapper.sol:_calcRewardIntegral(), bal - rewardRemaining can't underflow at line 222 as the conditional statement line 221 prevents it:

File: ConvexStakingWrapper.sol
221:         if (_supply > 0 && (bal - rewardRemaining) > 0) {
222:             rewardIntegral = uint128(rewardIntegral) + uint128(((bal - rewardRemaining) * 1e20) / _supply); //@audit-info (bal - rewardRemaining) can't underflow because of above if statement

This substraction should get computed inside an unchecked block and stored in a variable, which would then be used in the checked calculation for rewardIntegral.

Tools Used

VS Code

Recommended Mitigation Steps

Uncheck arithmetic operations when the risk of underflow or overflow is already contained by wrapping them in an unchecked block

code-423n4 / 2022-01-yield-findings