JS: Recognise that a less-than test is as good as a non-equal test for mitigating off-by-one array access #20423
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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 |
| @@ -33,6 +33,18 @@ ConditionGuardNode getLengthLEGuard(Variable index, Variable array) { | |||
| ) | |||
| } | |||
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| /** | |||
| * Gets a condition that checks that `index` is less than or equal to `array.length`. | |||
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The comment is incorrect. The function getLengthLTGuard checks for index < array.length (strictly less than), not less than or equal to. The comment should say 'Gets a condition that checks that index is less than array.length'.
Suggested change
| * Gets a condition that checks that `index` is less than or equal to `array.length`. | |
| * Gets a condition that checks that `index` is less than `array.length`. |
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…tigating off-by-one array access
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Drive-by fix noticed while looking through alleged bad autofixes (autofix used a
<test and CodeQL claimed it was an invalid fix)