Merge pull request #7097 from erik-krogh/railsReDoS

JS/PY/RB: support a limited number of ranges for ReDoS analysis

ruby/ql/lib/codeql/ruby/security/performance/ReDoSUtil.qll

@@ -539,6 +539,55 @@ private class EdgeLabel extends TInputSymbol {
   }
 }
 
+/**
+ * A RegExp term that acts like a plus.
+ * Either it's a RegExpPlus, or it is a range {1,X} where X is >= 30.
+ * 30 has been chosen as a threshold because for exponential blowup 2^30 is enough to get a decent DOS attack.
+ */
+private class EffectivelyPlus extends RegExpTerm {
+  EffectivelyPlus() {
+    this instanceof RegExpPlus
+    or
+    exists(RegExpRange range |
+      range.getLowerBound() = 1 and
+      (range.getUpperBound() >= 30 or not exists(range.getUpperBound()))
+    |
+      this = range
+    )
+  }
+}
+
+/**
+ * A RegExp term that acts like a star.
+ * Either it's a RegExpStar, or it is a range {0,X} where X is >= 30.
+ */
+private class EffectivelyStar extends RegExpTerm {
+  EffectivelyStar() {
+    this instanceof RegExpStar
+    or
+    exists(RegExpRange range |
+      range.getLowerBound() = 0 and
+      (range.getUpperBound() >= 30 or not exists(range.getUpperBound()))
+    |
+      this = range
+    )
+  }
+}
+
+/**
+ * A RegExp term that acts like a question mark.
+ * Either it's a RegExpQuestion, or it is a range {0,1}.
+ */
+private class EffectivelyQuestion extends RegExpTerm {
+  EffectivelyQuestion() {
+    this instanceof RegExpOpt
+    or
+    exists(RegExpRange range | range.getLowerBound() = 0 and range.getUpperBound() = 1 |
+      this = range
+    )
+  }
+}
+
 /**
  * Gets the state before matching `t`.
  */
@@ -559,14 +608,14 @@ State after(RegExpTerm t) {
   or
   exists(RegExpGroup grp | t = grp.getAChild() | result = after(grp))
   or
-  exists(RegExpStar star | t = star.getAChild() | result = before(star))
+  exists(EffectivelyStar star | t = star.getAChild() | result = before(star))
   or
-  exists(RegExpPlus plus | t = plus.getAChild() |
+  exists(EffectivelyPlus plus | t = plus.getAChild() |
     result = before(plus) or
     result = after(plus)
   )
   or
-  exists(RegExpOpt opt | t = opt.getAChild() | result = after(opt))
+  exists(EffectivelyQuestion opt | t = opt.getAChild() | result = after(opt))
   or
   exists(RegExpRoot root | t = root | result = AcceptAnySuffix(root))
 }
@@ -617,15 +666,17 @@ predicate delta(State q1, EdgeLabel lbl, State q2) {
   or
   exists(RegExpGroup grp | lbl = Epsilon() | q1 = before(grp) and q2 = before(grp.getChild(0)))
   or
-  exists(RegExpStar star | lbl = Epsilon() |
+  exists(EffectivelyStar star | lbl = Epsilon() |
     q1 = before(star) and q2 = before(star.getChild(0))
     or
     q1 = before(star) and q2 = after(star)
   )
   or
-  exists(RegExpPlus plus | lbl = Epsilon() | q1 = before(plus) and q2 = before(plus.getChild(0)))
+  exists(EffectivelyPlus plus | lbl = Epsilon() |
+    q1 = before(plus) and q2 = before(plus.getChild(0))
+  )
   or
-  exists(RegExpOpt opt | lbl = Epsilon() |
+  exists(EffectivelyQuestion opt | lbl = Epsilon() |
     q1 = before(opt) and q2 = before(opt.getChild(0))
     or
     q1 = before(opt) and q2 = after(opt)

ruby/ql/test/query-tests/security/cwe-1333-exponential-redos/tst.rb

@@ -362,11 +362,11 @@ bad84 = /^((?:a{0|-)|\w\{\d)+X$/
 bad85 = /^((?:a{0,|-)|\w\{\d,)+X$/
 bad86 = /^((?:a{0,2|-)|\w\{\d,\d)+X$/
 
-# GOOD: 
-good42 = /^((?:a{0,2}|-)|\w\{\d,\d\})+X$/
+# NOT GOOD 
+bad87 = /^((?:a{0,2}|-)|\w\{\d,\d\})+X$/
 
 # NOT GOOD
-bad87 = /^X(\u0061|a)*Y$/
+bad88 = /^X(\u0061|a)*Y$/
 
 # GOOD
 good43 = /^X(\u0061|b)+Y$/