First Flight #8: Math Master
First Flight #8
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Submission Details
Severity: low
Invalid

The lack of detailed comments further exacerbates the difficulty in understanding the assembly code, likelihood of introducing errors during maintenance or modification activities.

0xVinylDavyl

Summary

The MathMasters library incorporates assembly language in the sqrt function, contributing to decreased code readability. A refactoring effort or comprehensive comments are recommended to enhance code comprehension.

Vulnerability Details

The vulnerability arises from the utilization of assembly language within the sqrt function, impacting the readability of the code. Assembly language is inherently more complex and can be challenging, especially with low-level programming concepts. The lack of detailed comments further exacerbates the difficulty in understanding the assembly code.

###POC

/// @dev Returns the square root of `x`.
function sqrt(uint256 x) internal pure returns (uint256 z) {
/// @solidity memory-safe-assembly
assembly {
z := 181
​
​
// This segment is to get a reasonable initial estimate for the Babylonian method. With a bad
// start, the correct # of bits increases ~linearly each iteration instead of ~quadratically.
let r := shl(7, lt(87112285931760246646623899502532662132735, x))
r := or(r, shl(6, lt(4722366482869645213695, shr(r, x))))
r := or(r, shl(5, lt(1099511627775, shr(r, x))))
// Correct: 16777215 0xffffff
r := or(r, shl(4, lt(16777002, shr(r, x))))
z := shl(shr(1, r), z)
​
​
// There is no overflow risk here since `y < 2**136` after the first branch above.
z := shr(18, mul(z, add(shr(r, x), 65536))) // A `mul()` is saved from starting `z` at 181.
​
​
// Given the worst case multiplicative error of 2.84 above, 7 iterations should be enough.
z := shr(1, add(z, div(x, z)))
z := shr(1, add(z, div(x, z)))
z := shr(1, add(z, div(x, z)))
z := shr(1, add(z, div(x, z)))
z := shr(1, add(z, div(x, z)))
z := shr(1, add(z, div(x, z)))
z := shr(1, add(z, div(x, z)))
​
​
// If `x+1` is a perfect square, the Babylonian method cycles between
// `floor(sqrt(x))` and `ceil(sqrt(x))`. This statement ensures we return floor.
// See: https://en.wikipedia.org/wiki/Integer_square_root#Using_only_integer_division
z := sub(z, lt(div(x, z), z))
}
}
}

Impact

The assembly complexity in the sqrt function may impede code comprehension, making it challenging to grasp the logic and functionality of the code. This reduced readability increases the likelihood of introducing errors during maintenance or modification activities. Additionally, it may hinder collaboration among developers and potentially hinder the adoption of the library by other projects.

Tools Used

No specific tools were used to identify this vulnerability. Manual code review and analysis were conducted.

Recommendations

It is recommended to address the assembly complexity in the sqrt function through refactoring or by providing detailed comments to enhance code comprehension. Refactoring may involve restructuring the code using higher-level programming constructs to improve readability. Alternatively, comprehensive comments can be added to explain the purpose and functionality of the assembly code, aiding developers in understanding its intricacies.

/// @dev Returns the square root of `x`.
function sqrt(uint256 x) internal pure returns (uint256 z) {
/// @solidity memory-safe-assembly
assembly {
z := 181
// Assembly code for square root calculation
// ...
}
}

To address this vulnerability, the assembly code can be refactored into a more readable form using higher-level constructs, or detailed comments can be added to explain each step of the assembly logic. For example:

/// @dev Returns the square root of `x`.
function sqrt(uint256 x) internal pure returns (uint256 z) {
// Initial estimate for the Babylonian method
z := 181;
// Detailed comments explaining each step of the square root calculation
// ...
}

By improving the readability of the code, developers will find it easier to understand and maintain the functionality of the sqrt function.

Updates

Lead Judging Commences

inallhonesty Lead Judge over 1 year ago
Submission Judgement Published
Invalidated
Reason: Non-acceptable severity

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