Refine polynomial redos sources to exclude length limited methods

java/ql/lib/semmle/code/java/security/performance/PolynomialReDosQuery.qll

@@ -1,4 +1,4 @@
-/** Definitions and configurations for the Polynomial ReDos query */
+/** Definitions and configurations for the Polynomial ReDoS query */
 
 import semmle.code.java.security.performance.SuperlinearBackTracking
 import semmle.code.java.dataflow.DataFlow
@@ -16,6 +16,22 @@ class PolynomialRedosSink extends DataFlow::Node {
   RegExpTerm getRegExp() { result.getParent() = reg }
 }
 
+/**
+ * A method whose result typically has a limited length,
+ * such as HTTP headers, and values derrived from them.
+ */
+private class LengthRestrictedMethod extends Method {
+  LengthRestrictedMethod() {
+    this.getName().toLowerCase().matches(["%header%", "%requesturi%", "%requesturl%", "%cookie%"])
+    or
+    this.getDeclaringType().getName().toLowerCase().matches("%cookie%") and
+    this.getName().matches("get%")
+    or
+    this.getDeclaringType().getName().toLowerCase().matches("%request%") and
+    this.getName().toLowerCase().matches(["%get%path%", "get%user%", "%querystring%"])
+  }
+}
+
 /** A configuration for Polynomial ReDoS queries. */
 class PolynomialRedosConfig extends TaintTracking::Configuration {
   PolynomialRedosConfig() { this = "PolynomialRedosConfig" }
@@ -23,10 +39,17 @@ class PolynomialRedosConfig extends TaintTracking::Configuration {
   override predicate isSource(DataFlow::Node src) { src instanceof RemoteFlowSource }
 
   override predicate isSink(DataFlow::Node sink) { sink instanceof PolynomialRedosSink }
+
+  override predicate isSanitizer(DataFlow::Node node) {
+    super.isSanitizer(node) or
+    node.getType() instanceof PrimitiveType or
+    node.getType() instanceof BoxedType or
+    node.asExpr().(MethodAccess).getMethod() instanceof LengthRestrictedMethod
+  }
 }
 
 /** Holds if there is flow from `source` to `sink` that is matched against the regexp term `regexp` that is vulnerable to Polynomial ReDoS. */
-predicate hasPolynomialReDosResult(
+predicate hasPolynomialReDoSResult(
   DataFlow::PathNode source, DataFlow::PathNode sink, PolynomialBackTrackingTerm regexp
 ) {
   any(PolynomialRedosConfig config).hasFlowPath(source, sink) and

java/ql/src/Security/CWE/CWE-730/PolynomialReDoS.ql

@@ -12,11 +12,11 @@
  */
 
 import java
-import semmle.code.java.security.performance.PolynomialReDosQuery
+import semmle.code.java.security.performance.PolynomialReDoSQuery
 import DataFlow::PathGraph
 
 from DataFlow::PathNode source, DataFlow::PathNode sink, PolynomialBackTrackingTerm regexp
-where hasPolynomialReDosResult(source, sink, regexp)
+where hasPolynomialReDoSResult(source, sink, regexp)
 select sink, source, sink,
   "This $@ that depends on $@ may run slow on strings " + regexp.getPrefixMessage() +
     "with many repetitions of '" + regexp.getPumpString() + "'.", regexp, "regular expression",

java/ql/test/query-tests/security/CWE-730/PolyRedosTest.java

@@ -72,4 +72,13 @@ class PolyRedosTest {
         p3.asMatchPredicate().test(tainted); 
         p4.asPredicate().test(tainted); // $ hasPolyRedos
     }
+
+    void test6(HttpServletRequest request) {
+        Pattern p = Pattern.compile("^a*a*$");
+
+        p.matcher(request.getParameter("inp")).matches(); // $ hasPolyRedos
+        p.matcher(request.getHeader("If-None-Match")).matches();
+        p.matcher(request.getRequestURI()).matches();
+        p.matcher(request.getCookies()[0].getName()).matches();
+    }
 }

java/ql/test/query-tests/security/CWE-730/PolynomialReDoS.ql

@@ -1,6 +1,6 @@
 import java
 import TestUtilities.InlineExpectationsTest
-import semmle.code.java.security.performance.PolynomialReDosQuery
+import semmle.code.java.security.performance.PolynomialReDoSQuery
 
 class HasPolyRedos extends InlineExpectationsTest {
   HasPolyRedos() { this = "HasPolyRedos" }
@@ -10,7 +10,7 @@ class HasPolyRedos extends InlineExpectationsTest {
   override predicate hasActualResult(Location location, string element, string tag, string value) {
     tag = "hasPolyRedos" and
     exists(DataFlow::PathNode source, DataFlow::PathNode sink, PolynomialBackTrackingTerm regexp |
-      hasPolynomialReDosResult(source, sink, regexp) and
+      hasPolynomialReDoSResult(source, sink, regexp) and
       location = sink.getNode().getLocation() and
       element = sink.getNode().toString() and
       value = ""