JS: Recognise that a less-than test is as good as a non-equal test for mitigating off-by-one array access#20423
Merged
smowton merged 3 commits intogithub:mainfrom Sep 15, 2025
Conversation
Contributor
There was a problem hiding this comment.
Pull Request Overview
This PR enhances the JavaScript off-by-one array access detection by recognizing that a less-than test (<) provides the same protection as a not-equal test (!=) when mitigating off-by-one errors in array bounds checking.
- Added a new
getLengthLTGuardfunction to detectindex < array.lengthconditions - Updated the main query logic to exclude cases where either a not-equal or less-than guard exists
- Added test case demonstrating the fix with
i < a.lengthguard
Reviewed Changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.
| File | Description |
|---|---|
| javascript/ql/src/LanguageFeatures/LengthComparisonOffByOne.ql | Added getLengthLTGuard function and updated query to consider less-than guards |
| javascript/ql/test/query-tests/LanguageFeatures/LengthComparisonOffByOne/tst.js | Added test case for function with less-than guard to verify the fix |
…tigating off-by-one array access
smowton
force-pushed
the
smowton/fix/length-comparison-off-by-one-fp
branch
from
8c5afd2 to
db5c581
Compare
asgerf
approved these changes
Sep 15, 2025
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
2 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Drive-by fix noticed while looking through alleged bad autofixes (autofix used a
<test and CodeQL claimed it was an invalid fix)