JS/Python: Fix FP in redos related to empty lookaheads#6288
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erik-krogh merged 7 commits intogithub:mainfrom Aug 16, 2021
Merged
JS/Python: Fix FP in redos related to empty lookaheads#6288erik-krogh merged 7 commits intogithub:mainfrom
erik-krogh merged 7 commits intogithub:mainfrom
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LGTM I think it would be worth adding some test cases with a lookahead that just checks for an anchor, without an alternative that is also empty. That's one of the main cases where /(x*)+(?=$)/
/(x*)+(?=$|y)/
/([\s\S]*)+(?=$)/
/([\s\S]*)+(?=$|y)/ |
asgerf
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Jul 16, 2021
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| var bad91 = /([\s\S]*)+(?=$)/ | ||
| var bad92 = /([\s\S]*)+(?=$|y)/ No newline at end of file |
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I believe the last two ones should be marked as good? I'm not asking for the query to handle them, just that the test is accurate.
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You're right. I was a little fast there.
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asgerf
previously approved these changes
Aug 12, 2021
yoff
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Aug 16, 2021
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Just one thing to address. I also wonder if matchesEpsilon would be nicer as a member predicate on RegExpTerm, but I will not insist on that for this PR.
Co-authored-by: yoff <lerchedahl@gmail.com>
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Fixes #5964
Lookaheads/lookbehinds that match the empty string will always match, and they are thus pretty much useless and unnecessary.
However, I've now seen multiple regular expressions that have empty lookaheads.
The ReDoS query assumed that a lookahead had a rejecting suffix, but that assumptions breaks with lookaheads that match the empty string.
This PR fixes that by adding an epsilon transition across lookaheads/lookbehinds that match the empty string.
JavaScript evaluation looks fine
Python evaluation looks fine
I don't think this needs a change-note.