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refine isFork to remove false positive when a state has epsilon transition to itself

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This commit is contained in:
Erik Krogh Kristensen
2020-11-29 21:42:50 +01:00
parent d7b22e3b1b
commit 33b2701551
3 changed files with 20 additions and 3 deletions
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20
javascript/ql/src/Performance/ReDoS.ql
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@@ -705,7 +705,25 @@ predicate isFork(State q, InputSymbol s1, InputSymbol s2, State r1, State r2) {
or
r1 = r2 and
q1 = q2 and
epsilonSucc+(q) = q
epsilonSucc+(q) = q and
exists(RegExpTerm term | term = q.getRepr() | term instanceof InfiniteRepetitionQuantifier) and
(
// There is either multiple possible "mid" states.
count(State mid |
mid = epsilonSucc+(q) and
q = epsilonSucc+(mid) and
not mid = q
) > 2
or
// Or one of the mid states is an infinite quantifier itself
exists(State mid, RegExpTerm term |
mid = epsilonSucc+(q) and
q = epsilonSucc+(mid) and
not mid = q and
term = mid.getRepr() and
term instanceof InfiniteRepetitionQuantifier
)
)
) and
stateInsideBacktracking(r1) and
stateInsideBacktracking(r2)