Fix potential infinite loop in double wildcard processing

Fixes #4610

src/main/java/org/elasticsearch/common/regex/Regex.java

@@ -71,6 +71,9 @@ public class Regex {
             int nextIndex = pattern.indexOf('*', firstIndex + 1);
             if (nextIndex == -1) {
                 return str.endsWith(pattern.substring(1));
+            } else if (nextIndex == 1) {
+                // Double wildcard "**" - skipping the first "*"
+                return simpleMatch(pattern.substring(1), str);
             }
             String part = pattern.substring(1, nextIndex);
             int partIndex = str.indexOf(part);

src/test/java/org/elasticsearch/common/regex/RegexTests.java

@@ -25,6 +25,7 @@ import java.util.Random;
 import java.util.regex.Pattern;
 
 import static org.hamcrest.Matchers.equalTo;
+
 public class RegexTests extends ElasticsearchTestCase {
 
     @Test
@@ -53,4 +54,18 @@ public class RegexTests extends ElasticsearchTestCase {
             Pattern.compile("\\w\\d{1,2}", current); // accepts the flags?
         }
     }
+
+    @Test(timeout = 1000)
+    public void testDoubleWildcardMatch() {
+        assertTrue(Regex.simpleMatch("ddd", "ddd"));
+        assertTrue(Regex.simpleMatch("d*d*d", "dadd"));
+        assertTrue(Regex.simpleMatch("**ddd", "dddd"));
+        assertFalse(Regex.simpleMatch("**ddd", "fff"));
+        assertTrue(Regex.simpleMatch("fff*ddd", "fffabcddd"));
+        assertTrue(Regex.simpleMatch("fff**ddd", "fffabcddd"));
+        assertFalse(Regex.simpleMatch("fff**ddd", "fffabcdd"));
+        assertTrue(Regex.simpleMatch("fff*******ddd", "fffabcddd"));
+        assertFalse(Regex.simpleMatch("fff******ddd", "fffabcdd"));
+    }
+
 }