WW-4136 - Demonstrate proper input sanitizing for file download showcase example

- added demo code to prevent input paths containing "WEB-INF"

git-svn-id: https://svn.apache.org/repos/asf/struts/struts2/branches/STRUTS_2_3_15_X@1500082 13f79535-47bb-0310-9956-ffa450edef68

apps/showcase/src/main/java/org/apache/struts2/showcase/filedownload/FileDownloadAction.java

@@ -39,7 +39,23 @@ public class FileDownloadAction implements Action {
 	}
 
 	public void setInputPath(String value) {
-		inputPath = value;
+		inputPath = sanitizeInputPath(value);
+	}
+
+	/**
+	 * As the user modifiable parameter inputPath will be used to access server side resources, we want the path to be
+	 * sanitized - in this case it is demonstrated to disallow inputPath parameter values containing "WEB-INF". Consider to
+	 * use even stricter rules in production environments.
+	 *
+	 * @param value the raw parameter input value to sanitize
+	 *
+	 * @return the sanitized value; <tt>null</tt> if value contains an invalid path segment like WEB-INF
+	 */
+	String sanitizeInputPath( String value ) {
+		if (value != null && value.toUpperCase().contains("WEB-INF")) {
+			return null;
+		}
+		return value;
 	}
 
 	public InputStream getInputStream() throws Exception {

apps/showcase/src/test/java/org/apache/struts2/showcase/filedownload/FileDownloadActionTest.java

@@ -0,0 +1,42 @@
+package org.apache.struts2.showcase.filedownload;
+
+import org.junit.Before;
+import org.junit.Test;
+
+import static junit.framework.Assert.assertEquals;
+import static junit.framework.Assert.assertNull;
+
+public class FileDownloadActionTest {
+
+	private FileDownloadAction fileDownloadAction;
+
+	@Before
+	public void setUp() {
+	    this.fileDownloadAction = new FileDownloadAction();
+	}
+
+	@Test
+	public void testSanitizeInputPathShouldAllowSimpleParameter() throws Exception {
+		assertEquals("foo", fileDownloadAction.sanitizeInputPath("foo"));
+	}
+
+	@Test
+	public void testSanitizeInputPathShouldReturnNullForNullInput() throws Exception {
+		assertNull(fileDownloadAction.sanitizeInputPath(null));
+	}
+
+	@Test
+	public void testSanitizeInputPathShouldReturnNullForLeadingWebInf() throws Exception {
+		assertNull(fileDownloadAction.sanitizeInputPath("WEB-INF/foo"));
+	}
+
+	@Test
+	public void testSanitizeInputPathShouldReturnNullForNonLeadingWebInf() throws Exception {
+		assertNull(fileDownloadAction.sanitizeInputPath("./WEB-INF/foo"));
+	}
+
+	@Test
+	public void testSanitizeInputPathShouldReturnNullForNonUppercaseWebInf() throws Exception {
+		assertNull(fileDownloadAction.sanitizeInputPath("./wEB-Inf/foo"));
+	}
+}