First rev of Safe DOM

tools/dom/src/NodeValidatorBuilder.dart

+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+part of dart.dom.html;
+
+
+/**
+ * Class which helps construct standard node validation policies.
+ *
+ * By default this will not accept anything, but the 'allow*' functions can be
+ * used to expand what types of elements or attributes are allowed.
+ *
+ * All allow functions are additive- elements will be accepted if they are
+ * accepted by any specific rule.
+ *
+ * It is important to remember that sanitization is not just intended to prevent
+ * cross-site scripting attacks, but also to prevent information from being
+ * displayed in unexpected ways. For example something displaying basic
+ * formatted text may not expect `<video>` tags to appear. In this case an
+ * empty NodeValidatorBuilder with just [allowTextElements] might be
+ * appropriate.
+ */
+class NodeValidatorBuilder implements NodeValidator {
+
+  final List<NodeValidator> _validators = <NodeValidator>[];
+
+  NodeValidatorBuilder() {
+  }
+
+  /**
+   * Creates a new NodeValidatorBuilder which accepts common constructs.
+   *
+   * By default this will accept HTML5 elements and attributes with the default
+   * [UriPolicy] and templating elements.
+   *
+   * Notable syntax which is filtered:
+   *
+   * * Only known-good HTML5 elements and attributes are allowed.
+   * * All URLs must be same-origin, use [allowNavigation] and [allowImages] to
+   * specify additional URI policies.
+   * * Inline-styles are not allowed.
+   * * Custom element tags are disallowed, use [allowCustomElement].
+   * * Custom tags extensions are disallowed, use [allowTagExtension].
+   * * SVG Elements are not allowed, use [allowSvg].
+   *
+   * For scenarios where the HTML should only contain formatted text
+   * [allowTextElements] is more appropriate.
+   *
+   * Use [allowSvg] to allow SVG elements.
+   */
+  factory NodeValidatorBuilder.common() {

[Jennifer Messerly, 2013/08/17 06:07:07]

as a factory constructor, this is hard to use in a subclass. Perhaps:

NodeValidatorBuilder.common() {
  allowHtml5();
  allowTemplating();
}

[blois, 2013/08/19 22:02:09]

Done. Though most extension should be via composition rather than subclassing.

+    return new NodeValidatorBuilder()
+        ..allowHtml5()
+        ..allowTemplating();
+  }
+
+  /**
+   * Allows navigation elements- Form and Anchor tags, along with common
+   * attributes.
+   *
+   * The UriPolicy can be used to restrict the locations the navigation elements
+   * are allowed to direct to. By default this will use the default [UriPolicy].
+   */
+  void allowNavigation([UriPolicy uriPolicy]) {
+    if (uriPolicy == null) {
+      uriPolicy = new UriPolicy();
+    }
+    add(new _SimpleNodeValidator.allowNavigation(uriPolicy));
+  }
+
+  /**
+   * Allows image elements.
+   *
+   * The UriPolicy can be used to restrict the locations the images may be
+   * loaded from. By default this will use the default [UriPolicy].
+   */
+  void allowImages([UriPolicy uriPolicy]) {
+    if (uriPolicy == null) {
+      uriPolicy = new UriPolicy();
+    }
+    add(new _SimpleNodeValidator.allowImages(uriPolicy));
+  }
+
+  /**
+   * Allow basic text elements.
+   *
+   * This allows a subset of HTML5 elements, specifically just these tags and
+   * no attributes.
+   *
+   * * B
+   * * BLOCKQUOTE
+   * * BR
+   * * EM
+   * * H1
+   * * H2
+   * * H3
+   * * H4
+   * * H5
+   * * H6
+   * * HR
+   * * I
+   * * LI
+   * * OL
+   * * P
+   * * SPAN
+   * * UL
+   */
+  void allowTextElements() {
+    add(new _SimpleNodeValidator.allowTextElements());
+  }
+
+  /**
+   * Allow common safe HTML5 elements and attributes.
+   *
+   * This list is based off of the Caja whitelists at:
+   * https://code.google.com/p/google-caja/wiki/CajaWhitelists.
+   *
+   * Common things which are not allowed are script elements, style attributes
+   * and any script handlers.
+   */
+  void allowHtml5({UriPolicy uriPolicy}) {
+    add(new _Html5NodeValidator(uriPolicy: uriPolicy));
+  }
+
+  /**
+   * Allow SVG elements and attributes except for known bad ones.
+   */
+  void allowSvg() {
+    add(new _SvgNodeValidator());
+  }
+
+  /**
+   * Allow custom elements with the specified tag name and specified attributes.
+   *
+   * This will allow the elements as custom tags (such as <x-foo></x-foo>),
+   * but will not allow tag extensions. Use [allowTagExtension] to allow
+   * tag extensions.
+   */
+  void allowCustomElement(String tagName,
+      {UriPolicy uriPolicy,
+      Iterable<String> attributes,
+      Iterable<String> uriAttributes}) {
+
+    var tagNameUpper = tagName.toUpperCase();
+    var attrs;
+    if (attributes != null) {
+      attrs =
+          attributes.map((name) => '$tagNameUpper::${name.toLowerCase()}');
+    }
+    var uriAttrs;
+    if (uriAttributes != null) {
+      uriAttrs =
+          uriAttributes.map((name) => '$tagNameUpper::${name.toLowerCase()}');
+    }
+    if (uriPolicy == null) {
+      uriPolicy = new UriPolicy();
+    }
+
+    add(new _CustomElementNodeValidator(
+        uriPolicy,
+        [tagNameUpper],
+        attrs,
+        uriAttrs,
+        false,
+        true));
+  }
+
+  /**
+   * Allow custom tag extensions with the specified type name and specified
+   * attributes.
+   *
+   * This will allow tag extensions (such as <div is="x-foo"></div>),
+   * but will not allow custom tags. Use [allowCustomElement] to allow
+   * custom tags.
+   */
+  void allowTagExtension(String tagName, String baseName,
+      {UriPolicy uriPolicy,
+      Iterable<String> attributes,
+      Iterable<String> uriAttributes}) {
+
+    var baseNameUpper = baseName.toUpperCase();
+    var tagNameUpper = tagName.toUpperCase();
+    var attrs;
+    if (attributes != null) {
+      attrs =
+          attributes.map((name) => '$baseNameUpper::${name.toLowerCase()}');
+    }
+    var uriAttrs;
+    if (uriAttributes != null) {
+      uriAttrs =
+          uriAttributes.map((name) => '$baseNameUpper::${name.toLowerCase()}');
+    }
+    if (uriPolicy == null) {
+      uriPolicy = new UriPolicy();
+    }
+
+    add(new _CustomElementNodeValidator(
+        uriPolicy,
+        [tagNameUpper, baseNameUpper],
+        attrs,
+        uriAttrs,
+        true,
+        false));
+  }
+
+  void allowElement(String tagName, {UriPolicy uriPolicy,
+    Iterable<String> attributes,
+    Iterable<String> uriAttributes}) {
+
+    allowCustomElement(tagName, uriPolicy: uriPolicy,
+        attributes: attributes,
+        uriAttributes: uriAttributes);
+  }
+
+  /**
+   * Allow templating elements (such as <template> and template-related
+   * attributes.
+   *
+   * This still requires other validators to allow regular attributes to be
+   * bound (such as [allowHtml5]).
+   */
+  void allowTemplating() {
+    add(new _TemplatingNodeValidator());
+  }
+
+  /**
+   * Add an additional validator to the current list of validators.
+   *
+   * Elements and attributes will be accepted if they are accepted by any
+   * validators.
+   */
+  void add(NodeValidator validator) {
+    _validators.add(validator);
+  }
+
+  bool allowsElement(Element element) {
+    return _validators.any((v) => v.allowsElement(element));
+  }
+
+  bool allowsAttribute(Element element, String attributeName, String value) {
+    return _validators.any(
+        (v) => v.allowsAttribute(element, attributeName, value));
+  }
+}
+
+class _SimpleNodeValidator implements NodeValidator {
+  final Set<String> allowedElements;
+  final Set<String> allowedAttributes;
+  final Set<String> allowedUriAttributes;
+  final UriPolicy uriPolicy;
+
+  factory _SimpleNodeValidator.allowNavigation(UriPolicy uriPolicy) {
+    return new _SimpleNodeValidator(uriPolicy,
+      allowedElements: [
+        'A',
+        'FORM'],
+      allowedAttributes: [
+        'A::accesskey',
+        'A::coords',
+        'A::hreflang',
+        'A::name',
+        'A::shape',
+        'A::tabindex',
+        'A::target',
+        'A::type',
+        'FORM::accept',
+        'FORM::autocomplete',
+        'FORM::enctype',
+        'FORM::method',
+        'FORM::name',
+        'FORM::novalidate',
+        'FORM::target',
+      ],
+      allowedUriAttributes: [
+        'A::href',
+        'FORM::action',
+      ]);
+  }
+
+  factory _SimpleNodeValidator.allowImages(UriPolicy uriPolicy) {
+    return new _SimpleNodeValidator(uriPolicy,
+      allowedElements: [
+        'IMG'
+      ],
+      allowedAttributes: [
+        'IMG::align',
+        'IMG::alt',
+        'IMG::border',
+        'IMG::height',
+        'IMG::hspace',
+        'IMG::ismap',
+        'IMG::name',
+        'IMG::usemap',
+        'IMG::vspace',
+        'IMG::width',
+      ],
+      allowedUriAttributes: [
+        'IMG::src',
+      ]);
+  }
+
+  factory _SimpleNodeValidator.allowTextElements() {
+    return new _SimpleNodeValidator(null,
+      allowedElements: [
+        'B',
+        'BLOCKQUOTE',
+        'BR',
+        'EM',
+        'H1',
+        'H2',
+        'H3',
+        'H4',
+        'H5',
+        'H6',
+        'HR',
+        'I',
+        'LI',
+        'OL',
+        'P',
+        'SPAN',
+        'UL',
+      ]);
+  }
+
+  /**
+   * Elements must be uppercased tag names. For example `'IMG'`.
+   * Attributes must be uppercased tag name followed by :: followed by
+   * lowercase attribute name. For example `'IMG:src'`.
+   */
+  _SimpleNodeValidator(this.uriPolicy,
+      {Iterable<String> allowedElements, Iterable<String> allowedAttributes,
+      Iterable<String> allowedUriAttributes}):
+      this.allowedElements = allowedElements != null ?
+          new Set.from(allowedElements) : new Set(),
+      this.allowedAttributes = allowedAttributes != null ?
+          new Set.from(allowedAttributes) : new Set(),
+      this.allowedUriAttributes = allowedUriAttributes != null ?
+          new Set.from(allowedUriAttributes) : new Set();
+
+  bool allowsElement(Element element) {
+    return allowedElements.contains(element.tagName);
+  }
+
+  bool allowsAttribute(Element element, String attributeName, String value) {
+    var tagName = element.tagName;
+    if (allowedUriAttributes.contains('$tagName::$attributeName')) {
+      return uriPolicy.allowsUri(value);
+    } else if (allowedUriAttributes.contains('*::$attributeName')) {
+      return uriPolicy.allowsUri(value);
+    } else if (allowedAttributes.contains('$tagName::$attributeName')) {
+      return true;
+    } else if (allowedAttributes.contains('*::$attributeName')) {
+      return true;
+    } else if (allowedAttributes.contains('$tagName::*')) {
+      return true;
+    } else if (allowedAttributes.contains('*::*')) {
+      return true;
+    }
+    return false;
+  }
+}
+
+class _CustomElementNodeValidator extends _SimpleNodeValidator {
+  final bool allowTypeExtension;
+  final bool allowCustomTag;
+
+  _CustomElementNodeValidator(UriPolicy uriPolicy,
+      Iterable<String> allowedElements,
+      Iterable<String> allowedAttributes,
+      Iterable<String> allowedUriAttributes,
+      bool allowTypeExtension,
+      bool allowCustomTag):
+
+      super(uriPolicy,
+          allowedElements: allowedElements,
+          allowedAttributes: allowedAttributes,
+          allowedUriAttributes: allowedUriAttributes),
+      this.allowTypeExtension = allowTypeExtension == true,
+      this.allowCustomTag = allowCustomTag == true;
+
+  bool allowsElement(Element element) {
+    if (allowTypeExtension) {
+      var isAttr = element.attributes['is'];
+      if (isAttr != null) {
+        return allowedElements.contains(isAttr.toUpperCase()) &&
+          allowedElements.contains(element.tagName);
+      }
+    }
+    return allowCustomTag && allowedElements.contains(element.tagName);
+  }
+
+  bool allowsAttribute(Element element, String attributeName, String value) {
+   if (allowsElement(element)) {
+      if (allowTypeExtension && attributeName == 'is' &&
+          allowedElements.contains(value.toUpperCase())) {
+        return true;
+      }
+      return super.allowsAttribute(element, attributeName, value);
+    }
+    return false;
+  }
+}
+
+class _TemplatingNodeValidator extends _SimpleNodeValidator {
+  static const _TEMPLATE_ATTRS =
+      const <String>['bind', 'if', 'ref', 'repeat', 'syntax'];
+
+  final Set<String> _templateAttrs;
+
+  _TemplatingNodeValidator():
+      super(null,
+          allowedElements: [
+            'TEMPLATE'
+          ],
+          allowedAttributes: _TEMPLATE_ATTRS.map((attr) => 'TEMPLATE::$attr')),
+      _templateAttrs = new Set<String>.from(_TEMPLATE_ATTRS) {
+  }
+
+  bool allowsAttribute(Element element, String attributeName, String value) {
+    if (super.allowsAttribute(element, attributeName, value)) {
+      return true;
+    }
+
+    if (attributeName == 'template' && value == "") {
+      return true;
+    }
+
+    if (element.attributes['template'] == "" ) {
+      return _templateAttrs.contains(attributeName);
+    }
+    return false;
+  }
+}
+
+
+class _SvgNodeValidator implements NodeValidator {
+  bool allowsElement(Element element) {
+    if (element is svg.ScriptElement) {
+      return false;
+    }
+    if (element is svg.SvgElement) {
+      return true;
+    }
+    return false;
+  }
+
+  bool allowsAttribute(Element element, String attributeName, String value) {
+    if (attributeName == 'is' || attributeName.startsWith('on')) {
+      return false;
+    }
+    return allowsElement(element);
+  }
+}