Fix: catastrophic backtracking in astUtils linebreak regex (fixes #7893) #7898
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This fixes an issue where `astUtils.getLocationFromRangeIndex` and `astUtils.getRangeIndexFromLocation` were using a regular expression susceptible to catastrophic backtracking. The match would take quadratic time in the length of the last line of the file. Since the file in #7893 contains a 1.5 million character source map URL on the last line, rules like `no-multiple-empty-lines` would hang when using ast-utils to split the file into lines. This issue only applies to files without trailing newlines, and is only noticable when the last line of the file contains more than 30000 characters or so. Since only a few rules use these `astUtils` functions, this would only appear when either `no-useless-escape` or `no-multiple-empty-lines` reports an error for the file. Simplified example: Node 7.4.0 hangs when evaluating this expression. ```js /[^\n]*\n/.test('A'.repeat(1000000)) ```
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LGTM |
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@not-an-aardvark, thanks for your PR! By analyzing the history of the files in this pull request, we identified @mysticatea, @kaicataldo and @alangpierce to be potential reviewers. |
not-an-aardvark
added
accepted
vitorbal
reviewed
Jan 11, 2017
| @@ -309,6 +309,11 @@ ruleTester.run("no-multiple-empty-lines", rule, { | |||
| errors: [getExpectedError(1)], | |||
| options: [{ max: 1 }], | |||
| parserOptions: { ecmaVersion: 6 } | |||
| }, | |||
| { | |||
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Perhaps we could link to the related issue here, to make sure we don't forget about it?
nzakas
requested changes
Jan 11, 2017
| @@ -290,8 +290,13 @@ const lineIndexCache = new WeakMap(); | |||
| function getLineIndices(sourceCode) { | |||
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| if (!lineIndexCache.has(sourceCode)) { | |||
| const lineIndices = (sourceCode.text.match(/[^\r\n\u2028\u2029]*(\r\n|\r|\n|\u2028|\u2029)/g) || []) | |||
| .reduce((indices, line) => indices.concat(indices[indices.length - 1] + line.length), [0]); | |||
| const lineIndices = [0]; | |||
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Can you add a comment here explaining why it's done this way? I can see some well-meaning dev thinking they can simplify this and reverting accidentally.
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LGTM |
gyandeeps
approved these changes
Jan 11, 2017
kaicataldo
approved these changes
Jan 11, 2017
nzakas
approved these changes
Jan 12, 2017
This was referenced Jan 20, 2017
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What is the purpose of this pull request? (put an "X" next to item)
[x] Bug fix (see #7893)
What changes did you make? (Give an overview)
This fixes an issue where
astUtils.getLocationFromRangeIndexandastUtils.getRangeIndexFromLocationwere using a regular expression susceptible to catastrophic backtracking. The match would take quadratic time in the length of the last line of the file. Since the file in #7893 contains a 1.5 million character source map URL on the last line, rules likeno-multiple-empty-lineswould hang when using ast-utils to split the file into lines.This issue only applies to files without trailing newlines, and is only noticable when the last line of the file contains more than 30000 characters or so. Since only a few rules use these
astUtilsfunctions, this would only appear when eitherno-useless-escapeorno-multiple-empty-linesreports an error for the file.Simplified example: Node 7.4.0 hangs when evaluating this expression.
Is there anything you'd like reviewers to focus on?
Nothing in particular