Handle

Dravee

Vulnerability details

Impact

Increased gas cost

Proof of Concept

In L2LPTDataCache.sol:l1CirculatingSupply(), the code is as follows:

File: L2LPTDataCache.sol
88:     function l1CirculatingSupply() public view returns (uint256) {
89:         // After the first update from L1, l1TotalSupply should always be >= l2SupplyFromL1
90:         // The below check is defensive to avoid reverting if this invariant for some reason violated
91:         return
92:             l1TotalSupply >= l2SupplyFromL1
93:                 ? l1TotalSupply - l2SupplyFromL1
94:                 : 0;
95:     }

I suspect that statistically, the arithmetic operation l1TotalSupply - l2SupplyFromL1 should often be triggered. Therefore, caching the 2 variables l1TotalSupply and l2SupplyFromL1 in memory variables would save the 2 SLOADs (~200 gas) in the substraction and cost 4 MLOADs (~12 gas) and 2 MSTOREs (6 gas).

It can be done this way, as an example: (uint256 _l1TotalSupply, uint256 _l2SupplyFromL1) = (l1TotalSupply, l2SupplyFromL1);

Tools Used

VS Code

Recommended Mitigation Steps

Cache l1TotalSupply and l2SupplyFromL1 in local variables

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