limit the search of state-pairs to the ones that are reachable within the given length

javascript/ql/src/Performance/ReDoS.ql

@@ -799,6 +799,7 @@ string concretise(Trace t) {
  * a path from `r` back to `(fork, fork)` with `rem` steps.
  */
 predicate isReachableFromFork(State fork, StatePair r, Trace w, int rem) {
+  // base case
   exists(InputSymbol s1, InputSymbol s2, State q1, State q2 |
     isFork(fork, s1, s2, q1, q2) and
     r = MkStatePair(q1, q2) and
@@ -806,11 +807,12 @@ predicate isReachableFromFork(State fork, StatePair r, Trace w, int rem) {
     rem = statePairDist(r, MkStatePair(fork, fork))
   )
   or
+  // recursive case
   exists(StatePair p, Trace v, InputSymbol s1, InputSymbol s2 |
     isReachableFromFork(fork, p, v, rem + 1) and
     step(p, s1, s2, r) and
     w = Step(s1, s2, v) and
-    rem > 0
+    rem >= statePairDist(r, MkStatePair(fork, fork))
   )
 }
 

javascript/ql/test/query-tests/Performance/ReDoS/PolynomialBackTracking.expected

@@ -263,3 +263,8 @@
 | tst.js:251:18:251:19 | A* | it can start matching anywhere |
 | tst.js:251:18:251:19 | A* | it can start matching anywhere after the start of the preceeding 'A*' |
 | tst.js:260:14:260:21 | (\\n\\s*)+ | it can start matching anywhere |
+| tst.js:266:14:266:91 | (\\w*foobarbaz\\w*foobarbaz\\w*foobarbaz\\w*foobarbaz\\s*foobarbaz\\d*foobarbaz\\w*)+ | it can start matching anywhere |
+| tst.js:266:15:266:17 | \\w* | it can start matching anywhere |
+| tst.js:269:14:269:116 | (.thisisagoddamnlongstringforstresstestingthequery\|\\sthisisagoddamnlongstringforstresstestingthequery)* | it can start matching anywhere |
+| tst.js:272:14:272:77 | (thisisagoddamnlongstringforstresstestingthequery\|this\\w+query)* | it can start matching anywhere |
+| tst.js:275:15:275:117 | (thisisagoddamnlongstringforstresstestingthequery\|imanotherbutunrelatedstringcomparedtotheotherstring)* | it can start matching anywhere |

javascript/ql/test/query-tests/Performance/ReDoS/ReDoS.expected

@@ -113,3 +113,6 @@
 | tst.js:254:17:254:21 | [^>]+ | This part of the regular expression may cause exponential backtracking on strings containing many repetitions of '='. |
 | tst.js:257:16:257:21 | [^>a]+ | This part of the regular expression may cause exponential backtracking on strings containing many repetitions of '='. |
 | tst.js:260:17:260:19 | \\s* | This part of the regular expression may cause exponential backtracking on strings containing many repetitions of '\\n'. |
+| tst.js:266:87:266:89 | \\w* | This part of the regular expression may cause exponential backtracking on strings containing many repetitions of '0foobarbazfoobarbazfoobarbazfoobarbazfoobarbazfoobarbaz'. |
+| tst.js:269:14:269:116 | (.thisisagoddamnlongstringforstresstestingthequery\|\\sthisisagoddamnlongstringforstresstestingthequery)* | This part of the regular expression may cause exponential backtracking on strings containing many repetitions of ' thisisagoddamnlongstringforstresstestingthequery'. |
+| tst.js:272:14:272:77 | (thisisagoddamnlongstringforstresstestingthequery\|this\\w+query)* | This part of the regular expression may cause exponential backtracking on strings containing many repetitions of 'thisisagoddamnlongstringforstresstestingthequery'. |

javascript/ql/test/query-tests/Performance/ReDoS/tst.js

@@ -261,3 +261,15 @@ var bad58 = /(\n\s*)+$/;
 
 // GOOD
 var good26 = /([^\\\]]+)*/
+
+// NOT GOOD
+var bad59 = /(\w*foobarbaz\w*foobarbaz\w*foobarbaz\w*foobarbaz\s*foobarbaz\d*foobarbaz\w*)+-/;
+
+// NOT GOOD
+var bad60 = /(.thisisagoddamnlongstringforstresstestingthequery|\sthisisagoddamnlongstringforstresstestingthequery)*-/
+
+// NOT GOOD
+var bad61 = /(thisisagoddamnlongstringforstresstestingthequery|this\w+query)*-/
+
+// GOOD
+var good27 = /(thisisagoddamnlongstringforstresstestingthequery|imanotherbutunrelatedstringcomparedtotheotherstring)*-/