Clean duplicate separators in resource URLs

Most Servlet containers do this anyway, but not all, and not
consistently for forward and backslashes.

Issue: SPR-16616

spring-webflux/src/main/java/org/springframework/web/reactive/resource/ResourceWebHandler.java

@@ -328,7 +328,15 @@ public class ResourceWebHandler implements WebHandler, InitializingBean {
 		if (path.contains("%")) {
 			try {
 				// Use URLDecoder (vs UriUtils) to preserve potentially decoded UTF-8 chars
-				if (isInvalidPath(URLDecoder.decode(path, "UTF-8"))) {
+				String decodedPath = URLDecoder.decode(path, "UTF-8");
+				if (isInvalidPath(decodedPath)) {
+					if (logger.isTraceEnabled()) {
+						logger.trace("Ignoring invalid resource path with escape sequences [" + path + "].");
+					}
+					return Mono.empty();
+				}
+				decodedPath = processPath(decodedPath);
+				if (isInvalidPath(decodedPath)) {
 					if (logger.isTraceEnabled()) {
 						logger.trace("Ignoring invalid resource path with escape sequences [" + path + "].");
 					}
@@ -352,12 +360,47 @@ public class ResourceWebHandler implements WebHandler, InitializingBean {
 	}
 
 	/**
-	 * Process the given resource path to be used.
-	 * <p>The default implementation replaces any combination of leading '/' and
-	 * control characters (00-1F and 7F) with a single "/" or "". For example
-	 * {@code "  // /// ////  foo/bar"} becomes {@code "/foo/bar"}.
+	 * Process the given resource path.
+	 * <p>The default implementation replaces:
+	 * <ul>
+	 * <li>Backslash with forward slash.
+	 * <li>Duplicate occurrences of slash with a single slash.
+	 * <li>Any combination of leading slash and control characters (00-1F and 7F)
+	 * with a single "/" or "". For example {@code "  / // foo/bar"}
+	 * becomes {@code "/foo/bar"}.
+	 * </ul>
+	 * @since 3.2.12
 	 */
 	protected String processPath(String path) {
+		path = StringUtils.replace(path, "\\", "/");
+		path = cleanDuplicateSlashes(path);
+		return cleanLeadingSlash(path);
+	}
+
+	private String cleanDuplicateSlashes(String path) {
+		StringBuilder sb = null;
+		char prev = 0;
+		for (int i = 0; i < path.length(); i++) {
+			char curr = path.charAt(i);
+			try {
+				if ((curr == '/') && (prev == '/')) {
+					if (sb == null) {
+						sb = new StringBuilder(path.substring(0, i));
+					}
+					continue;
+				}
+				if (sb != null) {
+					sb.append(path.charAt(i));
+				}
+			}
+			finally {
+				prev = curr;
+			}
+		}
+		return sb != null ? sb.toString() : path;
+	}
+
+	private String cleanLeadingSlash(String path) {
 		boolean slash = false;
 		for (int i = 0; i < path.length(); i++) {
 			if (path.charAt(i) == '/') {

spring-webflux/src/test/java/org/springframework/web/reactive/resource/ResourceWebHandlerTests.java

@@ -54,13 +54,10 @@ import org.springframework.web.server.MethodNotAllowedException;
 import org.springframework.web.server.ResponseStatusException;
 import org.springframework.web.server.ServerWebExchange;
 
-import static org.hamcrest.Matchers.instanceOf;
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertNull;
-import static org.junit.Assert.assertSame;
-import static org.junit.Assert.assertThat;
-import static org.junit.Assert.assertTrue;
-import static org.junit.Assert.fail;
+import static org.hamcrest.Matchers.*;
+import static org.junit.Assert.*;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.*;
 
 /**
  * Unit tests for {@link ResourceWebHandler}.
@@ -240,39 +237,85 @@ public class ResourceWebHandlerTests {
 	}
 
 	@Test
-	public void invalidPath() throws Exception {
+	public void testInvalidPath() throws Exception {
+
+		// Use mock ResourceResolver: i.e. we're only testing upfront validations...
+
+		Resource resource = mock(Resource.class);
+		when(resource.getFilename()).thenThrow(new AssertionError("Resource should not be resolved"));
+		when(resource.getInputStream()).thenThrow(new AssertionError("Resource should not be resolved"));
+		ResourceResolver resolver = mock(ResourceResolver.class);
+		when(resolver.resolveResource(any(), any(), any(), any())).thenReturn(Mono.just(resource));
+
+		ResourceWebHandler handler = new ResourceWebHandler();
+		handler.setLocations(Collections.singletonList(new ClassPathResource("test/", getClass())));
+		handler.setResourceResolvers(Collections.singletonList(resolver));
+		handler.afterPropertiesSet();
+
+		testInvalidPath("../testsecret/secret.txt", handler);
+		testInvalidPath("test/../../testsecret/secret.txt", handler);
+		testInvalidPath(":/../../testsecret/secret.txt", handler);
+
+		Resource location = new UrlResource(getClass().getResource("./test/"));
+		this.handler.setLocations(Collections.singletonList(location));
+		Resource secretResource = new UrlResource(getClass().getResource("testsecret/secret.txt"));
+		String secretPath = secretResource.getURL().getPath();
+
+		testInvalidPath("file:" + secretPath, handler);
+		testInvalidPath("/file:" + secretPath, handler);
+		testInvalidPath("url:" + secretPath, handler);
+		testInvalidPath("/url:" + secretPath, handler);
+		testInvalidPath("/../.." + secretPath, handler);
+		testInvalidPath("/%2E%2E/testsecret/secret.txt", handler);
+		testInvalidPath("/%2E%2E/testsecret/secret.txt", handler);
+		testInvalidPath("%2F%2F%2E%2E%2F%2F%2E%2E" + secretPath, handler);
+	}
+
+	private void testInvalidPath(String requestPath, ResourceWebHandler handler) {
+		ServerWebExchange exchange = MockServerWebExchange.from(MockServerHttpRequest.get(""));
+		setPathWithinHandlerMapping(exchange, requestPath);
+		StepVerifier.create(handler.handle(exchange))
+				.expectErrorSatisfies(err -> {
+					assertThat(err, instanceOf(ResponseStatusException.class));
+					assertEquals(HttpStatus.NOT_FOUND, ((ResponseStatusException) err).getStatus());
+				}).verify(TIMEOUT);
+	}
+
+	@Test
+	public void testResolvePathWithTraversal() throws Exception {
 		for (HttpMethod method : HttpMethod.values()) {
-			testInvalidPath(method);
+			testResolvePathWithTraversal(method);
 		}
 	}
 
-	private void testInvalidPath(HttpMethod httpMethod) throws Exception {
+	private void testResolvePathWithTraversal(HttpMethod httpMethod) throws Exception {
 		Resource location = new ClassPathResource("test/", getClass());
 		this.handler.setLocations(Collections.singletonList(location));
 
-		testInvalidPath(httpMethod, "../testsecret/secret.txt", location);
-		testInvalidPath(httpMethod, "test/../../testsecret/secret.txt", location);
-		testInvalidPath(httpMethod, ":/../../testsecret/secret.txt", location);
+		testResolvePathWithTraversal(httpMethod, "../testsecret/secret.txt", location);
+		testResolvePathWithTraversal(httpMethod, "test/../../testsecret/secret.txt", location);
+		testResolvePathWithTraversal(httpMethod, ":/../../testsecret/secret.txt", location);
 
 		location = new UrlResource(getClass().getResource("./test/"));
 		this.handler.setLocations(Collections.singletonList(location));
 		Resource secretResource = new UrlResource(getClass().getResource("testsecret/secret.txt"));
 		String secretPath = secretResource.getURL().getPath();
 
-		testInvalidPath(httpMethod, "file:" + secretPath, location);
-		testInvalidPath(httpMethod, "/file:" + secretPath, location);
-		testInvalidPath(httpMethod, "url:" + secretPath, location);
-		testInvalidPath(httpMethod, "/url:" + secretPath, location);
-		testInvalidPath(httpMethod, "////../.." + secretPath, location);
-		testInvalidPath(httpMethod, "/%2E%2E/testsecret/secret.txt", location);
-		testInvalidPath(httpMethod, "url:" + secretPath, location);
+		testResolvePathWithTraversal(httpMethod, "file:" + secretPath, location);
+		testResolvePathWithTraversal(httpMethod, "/file:" + secretPath, location);
+		testResolvePathWithTraversal(httpMethod, "url:" + secretPath, location);
+		testResolvePathWithTraversal(httpMethod, "/url:" + secretPath, location);
+		testResolvePathWithTraversal(httpMethod, "////../.." + secretPath, location);
+		testResolvePathWithTraversal(httpMethod, "/%2E%2E/testsecret/secret.txt", location);
+		testResolvePathWithTraversal(httpMethod, "%2F%2F%2E%2E%2F%2Ftestsecret/secret.txt", location);
+		testResolvePathWithTraversal(httpMethod, "url:" + secretPath, location);
 
 		// The following tests fail with a MalformedURLException on Windows
-		// testInvalidPath(location, "/" + secretPath);
-		// testInvalidPath(location, "/  " + secretPath);
+		// testResolvePathWithTraversal(location, "/" + secretPath);
+		// testResolvePathWithTraversal(location, "/  " + secretPath);
 	}
 
-	private void testInvalidPath(HttpMethod httpMethod, String requestPath, Resource location) throws Exception {
+	private void testResolvePathWithTraversal(HttpMethod httpMethod, String requestPath, Resource location) throws Exception {
 		ServerWebExchange exchange = MockServerWebExchange.from(MockServerHttpRequest.method(httpMethod, ""));
 		setPathWithinHandlerMapping(exchange, requestPath);
 		StepVerifier.create(this.handler.handle(exchange))

spring-webmvc/src/main/java/org/springframework/web/servlet/resource/ResourceHttpRequestHandler.java

@@ -520,7 +520,15 @@ public class ResourceHttpRequestHandler extends WebContentGenerator
 		if (path.contains("%")) {
 			try {
 				// Use URLDecoder (vs UriUtils) to preserve potentially decoded UTF-8 chars
-				if (isInvalidPath(URLDecoder.decode(path, "UTF-8"))) {
+				String decodedPath = URLDecoder.decode(path, "UTF-8");
+				if (isInvalidPath(decodedPath)) {
+					if (logger.isTraceEnabled()) {
+						logger.trace("Ignoring invalid resource path with escape sequences [" + path + "].");
+					}
+					return null;
+				}
+				decodedPath = processPath(decodedPath);
+				if (isInvalidPath(decodedPath)) {
 					if (logger.isTraceEnabled()) {
 						logger.trace("Ignoring invalid resource path with escape sequences [" + path + "].");
 					}
@@ -543,13 +551,47 @@ public class ResourceHttpRequestHandler extends WebContentGenerator
 	}
 
 	/**
-	 * Process the given resource path to be used.
-	 * <p>The default implementation replaces any combination of leading '/' and
-	 * control characters (00-1F and 7F) with a single "/" or "". For example
-	 * {@code "  // /// ////  foo/bar"} becomes {@code "/foo/bar"}.
+	 * Process the given resource path.
+	 * <p>The default implementation replaces:
+	 * <ul>
+	 * <li>Backslash with forward slash.
+	 * <li>Duplicate occurrences of slash with a single slash.
+	 * <li>Any combination of leading slash and control characters (00-1F and 7F)
+	 * with a single "/" or "". For example {@code "  / // foo/bar"}
+	 * becomes {@code "/foo/bar"}.
+	 * </ul>
 	 * @since 3.2.12
 	 */
 	protected String processPath(String path) {
+		path = StringUtils.replace(path, "\\", "/");
+		path = cleanDuplicateSlashes(path);
+		return cleanLeadingSlash(path);
+	}
+
+	private String cleanDuplicateSlashes(String path) {
+		StringBuilder sb = null;
+		char prev = 0;
+		for (int i = 0; i < path.length(); i++) {
+			char curr = path.charAt(i);
+			try {
+				if ((curr == '/') && (prev == '/')) {
+					if (sb == null) {
+						sb = new StringBuilder(path.substring(0, i));
+					}
+					continue;
+				}
+				if (sb != null) {
+					sb.append(path.charAt(i));
+				}
+			}
+			finally {
+				prev = curr;
+			}
+		}
+		return sb != null ? sb.toString() : path;
+	}
+
+	private String cleanLeadingSlash(String path) {
 		boolean slash = false;
 		for (int i = 0; i < path.length(); i++) {
 			if (path.charAt(i) == '/') {

spring-webmvc/src/test/java/org/springframework/web/servlet/resource/ResourceHttpRequestHandlerTests.java

@@ -43,6 +43,7 @@ import org.springframework.web.accept.ContentNegotiationManagerFactoryBean;
 import org.springframework.web.servlet.HandlerMapping;
 
 import static org.junit.Assert.*;
+import static org.mockito.Mockito.*;
 
 /**
  * Unit tests for {@link ResourceHttpRequestHandler}.
@@ -303,41 +304,84 @@ public class ResourceHttpRequestHandlerTests {
 	}
 
 	@Test
-	public void invalidPath() throws Exception {
+	public void testInvalidPath() throws Exception {
+
+		// Use mock ResourceResolver: i.e. we're only testing upfront validations...
+
+		Resource resource = mock(Resource.class);
+		when(resource.getFilename()).thenThrow(new AssertionError("Resource should not be resolved"));
+		when(resource.getInputStream()).thenThrow(new AssertionError("Resource should not be resolved"));
+		ResourceResolver resolver = mock(ResourceResolver.class);
+		when(resolver.resolveResource(any(), any(), any(), any())).thenReturn(resource);
+
+		ResourceHttpRequestHandler handler = new ResourceHttpRequestHandler();
+		handler.setLocations(Collections.singletonList(new ClassPathResource("test/", getClass())));
+		handler.setResourceResolvers(Collections.singletonList(resolver));
+		handler.setServletContext(new TestServletContext());
+		handler.afterPropertiesSet();
+
+		testInvalidPath("../testsecret/secret.txt", handler);
+		testInvalidPath("test/../../testsecret/secret.txt", handler);
+		testInvalidPath(":/../../testsecret/secret.txt", handler);
+
+		Resource location = new UrlResource(getClass().getResource("./test/"));
+		this.handler.setLocations(Collections.singletonList(location));
+		Resource secretResource = new UrlResource(getClass().getResource("testsecret/secret.txt"));
+		String secretPath = secretResource.getURL().getPath();
+
+		testInvalidPath("file:" + secretPath, handler);
+		testInvalidPath("/file:" + secretPath, handler);
+		testInvalidPath("url:" + secretPath, handler);
+		testInvalidPath("/url:" + secretPath, handler);
+		testInvalidPath("/../.." + secretPath, handler);
+		testInvalidPath("/%2E%2E/testsecret/secret.txt", handler);
+		testInvalidPath("/%2E%2E/testsecret/secret.txt", handler);
+		testInvalidPath("%2F%2F%2E%2E%2F%2F%2E%2E" + secretPath, handler);
+	}
+
+	private void testInvalidPath(String requestPath, ResourceHttpRequestHandler handler) throws Exception {
+		this.request.setAttribute(HandlerMapping.PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE, requestPath);
+		this.response = new MockHttpServletResponse();
+		handler.handleRequest(this.request, this.response);
+		assertEquals(HttpStatus.NOT_FOUND.value(), this.response.getStatus());
+	}
+
+	@Test
+	public void resolvePathWithTraversal() throws Exception {
 		for (HttpMethod method : HttpMethod.values()) {
 			this.request = new MockHttpServletRequest("GET", "");
 			this.response = new MockHttpServletResponse();
-			testInvalidPath(method);
+			testResolvePathWithTraversal(method);
 		}
 	}
 
-	private void testInvalidPath(HttpMethod httpMethod) throws Exception {
+	private void testResolvePathWithTraversal(HttpMethod httpMethod) throws Exception {
 		this.request.setMethod(httpMethod.name());
 
 		Resource location = new ClassPathResource("test/", getClass());
 		this.handler.setLocations(Collections.singletonList(location));
 
-		testInvalidPath(location, "../testsecret/secret.txt");
-		testInvalidPath(location, "test/../../testsecret/secret.txt");
-		testInvalidPath(location, ":/../../testsecret/secret.txt");
+		testResolvePathWithTraversal(location, "../testsecret/secret.txt");
+		testResolvePathWithTraversal(location, "test/../../testsecret/secret.txt");
+		testResolvePathWithTraversal(location, ":/../../testsecret/secret.txt");
 
 		location = new UrlResource(getClass().getResource("./test/"));
 		this.handler.setLocations(Collections.singletonList(location));
 		Resource secretResource = new UrlResource(getClass().getResource("testsecret/secret.txt"));
 		String secretPath = secretResource.getURL().getPath();
 
-		testInvalidPath(location, "file:" + secretPath);
-		testInvalidPath(location, "/file:" + secretPath);
-		testInvalidPath(location, "url:" + secretPath);
-		testInvalidPath(location, "/url:" + secretPath);
-		testInvalidPath(location, "/" + secretPath);
-		testInvalidPath(location, "////../.." + secretPath);
-		testInvalidPath(location, "/%2E%2E/testsecret/secret.txt");
-		testInvalidPath(location, "/  " + secretPath);
-		testInvalidPath(location, "url:" + secretPath);
+		testResolvePathWithTraversal(location, "file:" + secretPath);
+		testResolvePathWithTraversal(location, "/file:" + secretPath);
+		testResolvePathWithTraversal(location, "url:" + secretPath);
+		testResolvePathWithTraversal(location, "/url:" + secretPath);
+		testResolvePathWithTraversal(location, "/" + secretPath);
+		testResolvePathWithTraversal(location, "////../.." + secretPath);
+		testResolvePathWithTraversal(location, "/%2E%2E/testsecret/secret.txt");
+		testResolvePathWithTraversal(location, "%2F%2F%2E%2E%2F%2Ftestsecret/secret.txt");
+		testResolvePathWithTraversal(location, "/  " + secretPath);
 	}
 
-	private void testInvalidPath(Resource location, String requestPath) throws Exception {
+	private void testResolvePathWithTraversal(Resource location, String requestPath) throws Exception {
 		this.request.setAttribute(HandlerMapping.PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE, requestPath);
 		this.response = new MockHttpServletResponse();
 		this.handler.handleRequest(this.request, this.response);
@@ -356,7 +400,8 @@ public class ResourceHttpRequestHandlerTests {
 	}
 
 	@Test
-	public void processPath() throws Exception {
+	public void processPath() {
+		// Unchanged
 		assertSame("/foo/bar", this.handler.processPath("/foo/bar"));
 		assertSame("foo/bar", this.handler.processPath("foo/bar"));
 
@@ -382,10 +427,17 @@ public class ResourceHttpRequestHandlerTests {
 		assertEquals("/", this.handler.processPath("/"));
 		assertEquals("/", this.handler.processPath("///"));
 		assertEquals("/", this.handler.processPath("/ /   / "));
+		assertEquals("/", this.handler.processPath("\\/ \\/   \\/ "));
+
+		// duplicate slash or backslash
+		assertEquals("/foo/ /bar/baz/", this.handler.processPath("//foo/ /bar//baz//"));
+		assertEquals("/foo/ /bar/baz/", this.handler.processPath("\\\\foo\\ \\bar\\\\baz\\\\"));
+		assertEquals("foo/bar", this.handler.processPath("foo\\\\/\\////bar"));
+
 	}
 
 	@Test
-	public void initAllowedLocations() throws Exception {
+	public void initAllowedLocations() {
 		PathResourceResolver resolver = (PathResourceResolver) this.handler.getResourceResolvers().get(0);
 		Resource[] locations = resolver.getAllowedLocations();