First Flight #8: Math Master
First Flight #8
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100 EXP
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Submission Details
Severity: high
Valid

Wrong `if` condition that evaluates always to zero.

4th05

Summary

There is a wrong if condition which evaluates always to zero at line 52. The binary result of the or is always gt than x and the function never reverts (due to the if statement), even if there is an overflow of the variable type uint256.

Vulnerability Details

The check of the if condition, is incorrect. mulWadUp fuction will never revert (due to the if statement), because the result of the or is always gt than x.

function mulWadUp(uint256 x, uint256 y) internal pure returns (uint256 z) {
/// @solidity memory-safe-assembly
assembly {
// Equivalent to `require(y == 0 || x <= type(uint256).max / y)`.
if mul(y, gt(x, or(div(not(0), y), x))) {
mstore(0x40, 0xbac65e5b) // `MathMasters__MulWadFailed()`.
revert(0x1c, 0x04)
}
if iszero(sub(div(add(z, x), y), 1)) { x := add(x, 1) }
z := add(iszero(iszero(mod(mul(x, y), WAD))), div(mul(x, y), WAD))
}
}

Impact

This bug cause the function to do not revert in case of overflow of the variable uint256 and therefore giving wrong results to the user.

Tools Used

Manual review and Remix

Recommendations

Remove from line 52 the or statement from the if condition.

function mulWadUp(uint256 x, uint256 y) internal pure returns (uint256 z) {
/// @solidity memory-safe-assembly
assembly {
// Equivalent to `require(y == 0 || x <= type(uint256).max / y)`.
- if mul(y, gt(x, or(div(not(0), y), x))) {
+ if mul(y, gt(x, div(not(0), y))) {
mstore(0x40, 0xbac65e5b) // `MathMasters__MulWadFailed()`.
revert(0x1c, 0x04)
}
if iszero(sub(div(add(z, x), y), 1)) { x := add(x, 1) }
z := add(iszero(iszero(mod(mul(x, y), WAD))), div(mul(x, y), WAD))
}
}
Updates

Lead Judging Commences

inallhonesty Lead Judge almost 2 years ago
Submission Judgement Published
Validated
Assigned finding tags:

`mulWadUp` has a bad overflow check

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