[SPARK-24542][SQL] UDF series UDFXPathXXXX allow users to pass carefully crafted XML to access arbitrary files

## What changes were proposed in this pull request?

UDF series UDFXPathXXXX allow users to pass carefully crafted XML to access arbitrary files. Spark does not have built-in access control. When users use the external access control library, users might bypass them and access the file contents.

This PR basically patches the Hive fix to Apache Spark. https://issues.apache.org/jira/browse/HIVE-18879

## How was this patch tested?

A unit test case

Author: Xiao Li <[email protected]>

Closes apache#21549 from gatorsmile/xpathSecurity.

Author: gatorsmile

sql/catalyst/src/main/java/org/apache/spark/sql/catalyst/expressions/xml/UDFXPathUtil.java

@@ -21,6 +21,9 @@
 import java.io.Reader;
 
 import javax.xml.namespace.QName;
+import javax.xml.parsers.DocumentBuilder;
+import javax.xml.parsers.DocumentBuilderFactory;
+import javax.xml.parsers.ParserConfigurationException;
 import javax.xml.xpath.XPath;
 import javax.xml.xpath.XPathConstants;
 import javax.xml.xpath.XPathExpression;
@@ -37,9 +40,15 @@
  * This is based on Hive's UDFXPathUtil implementation.
  */
 public class UDFXPathUtil {
+  public static final String SAX_FEATURE_PREFIX = "http://xml.org/sax/features/";
+  public static final String EXTERNAL_GENERAL_ENTITIES_FEATURE = "external-general-entities";
+  public static final String EXTERNAL_PARAMETER_ENTITIES_FEATURE = "external-parameter-entities";
+  private DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
+  private DocumentBuilder builder = null;
   private XPath xpath = XPathFactory.newInstance().newXPath();
   private ReusableStringReader reader = new ReusableStringReader();
   private InputSource inputSource = new InputSource(reader);
+
   private XPathExpression expression = null;
   private String oldPath = null;
 
@@ -65,14 +74,31 @@ public Object eval(String xml, String path, QName qname) throws XPathExpressionE
       return null;
     }
 
+    if (builder == null){
+      try {
+        initializeDocumentBuilderFactory();
+        builder = dbf.newDocumentBuilder();
+      } catch (ParserConfigurationException e) {
+        throw new RuntimeException(
+          "Error instantiating DocumentBuilder, cannot build xml parser", e);
+      }
+    }
+
     reader.set(xml);
     try {
-      return expression.evaluate(inputSource, qname);
+      return expression.evaluate(builder.parse(inputSource), qname);
     } catch (XPathExpressionException e) {
       throw new RuntimeException("Invalid XML document: " + e.getMessage() + "\n" + xml, e);
+    } catch (Exception e) {
+      throw new RuntimeException("Error loading expression '" + oldPath + "'", e);
     }
   }
 
+  private void initializeDocumentBuilderFactory() throws ParserConfigurationException {
+    dbf.setFeature(SAX_FEATURE_PREFIX + EXTERNAL_GENERAL_ENTITIES_FEATURE, false);
+    dbf.setFeature(SAX_FEATURE_PREFIX + EXTERNAL_PARAMETER_ENTITIES_FEATURE, false);
+  }
+
   public Boolean evalBoolean(String xml, String path) throws XPathExpressionException {
     return (Boolean) eval(xml, path, XPathConstants.BOOLEAN);
   }

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/xml/UDFXPathUtilSuite.scala

@@ -77,6 +77,27 @@ class UDFXPathUtilSuite extends SparkFunSuite {
     assert(ret == "foo")
   }
 
+  test("embedFailure") {
+    import org.apache.commons.io.FileUtils
+    import java.io.File
+    val secretValue = String.valueOf(Math.random)
+    val tempFile = File.createTempFile("verifyembed", ".tmp")
+    tempFile.deleteOnExit()
+    val fname = tempFile.getAbsolutePath
+
+    FileUtils.writeStringToFile(tempFile, secretValue)
+
+    val xml =
+      s"""<?xml version="1.0" encoding="utf-8"?>
+        |<!DOCTYPE test [
+        |    <!ENTITY embed SYSTEM "$fname">
+        |]>
+        |<foo>&embed;</foo>
+      """.stripMargin
+    val evaled = new UDFXPathUtil().evalString(xml, "/foo")
+    assert(evaled.isEmpty)
+  }
+
   test("number eval") {
     var ret =
       util.evalNumber("<a><b>true</b><b>false</b><b>b3</b><c>c1</c><c>-77</c></a>", "a/c[2]")

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/xml/XPathExpressionSuite.scala

@@ -40,8 +40,9 @@ class XPathExpressionSuite extends SparkFunSuite with ExpressionEvalHelper {
 
     // Test error message for invalid XML document
     val e1 = intercept[RuntimeException] { testExpr("<a>/a>", "a", null.asInstanceOf[T]) }
-    assert(e1.getCause.getMessage.contains("Invalid XML document") &&
-      e1.getCause.getMessage.contains("<a>/a>"))
+    assert(e1.getCause.getCause.getMessage.contains(
+      "XML document structures must start and end within the same entity."))
+    assert(e1.getMessage.contains("<a>/a>"))
 
     // Test error message for invalid xpath
     val e2 = intercept[RuntimeException] { testExpr("<a></a>", "!#$", null.asInstanceOf[T]) }