100 EXP
Submission Details
Impact:
Likelihood:
BalanceOf function contain a useless `mstore`.
Author Revealed upon completion
Root + Impact
In the _balanceOf function there is a mstore that is not necessary
Description
-
The _balanceOf function is a major function in the contract that is called multiple times throughout the contract's life.
-
Any bloating in the code in that function can lead to increasing gas spent.
// Root cause in the codebase with @> marks to highlight the relevant section
function _balanceOf(address owner) internal view returns (uint256) {
assembly {
if iszero(owner) {
revert(0, 0)
}
let baseSlot := _balances.slot
let ptr := mload(0x40)
mstore(ptr, owner)
mstore(add(ptr, 0x20), baseSlot)
let dataSlot := keccak256(ptr, 0x40)
let amount := sload(dataSlot)
mstore(ptr, amount)
@> mstore(add(ptr, 0x20), 0)
return(ptr, 0x20)
}
}
Risk
Likelihood:
Every time someone calls _balanceOf will cause to spent more gas than needed.
Impact:
-
More gas spended than needed.
-
Code bloating.
Proof of Concept
Leave the function like this and run the tests, all tests will pass.
function _balanceOf(address owner) internal view returns (uint256) {
assembly {
if iszero(owner) {
revert(0, 0)
}
let baseSlot := _balances.slot
let ptr := mload(0x40)
mstore(ptr, owner)
mstore(add(ptr, 0x20), baseSlot)
let dataSlot := keccak256(ptr, 0x40)
let amount := sload(dataSlot)
mstore(ptr, amount)
return(ptr, 0x20)
}
}
Recommended Mitigation
function _balanceOf(address owner) internal view returns (uint256) {
assembly {
if iszero(owner) {
revert(0, 0)
}
let baseSlot := _balances.slot
let ptr := mload(0x40)
mstore(ptr, owner)
mstore(add(ptr, 0x20), baseSlot)
let dataSlot := keccak256(ptr, 0x40)
let amount := sload(dataSlot)
mstore(ptr, amount)
- mstore(add(ptr, 0x20), 0)
return(ptr, 0x20)
}
}
Rewards breakdown
nSLOC
222This contest has a flat reward structure with the following payouts:
100 EXP
20 EXP
2 EXP
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