Prevent CSRF uploads via /file/dropupload/

Summary:
We don't currently validate CSRF tokens on this workflow. This allows an
attacker to upload arbitrary files on the user's behalf. Although I believe the
tight list of servable mime-types means that's more or less the end of the
attack, this is still a vulnerability.

In the long term, the right solution is probably to pass CSRF tokens on all Ajax
requests in an HTTP header (or just a GET param) or something like that.
However, this endpoint is unique and this is the quickest and most direct way to
close the hole.

Test Plan:
  - Drop-uploaded files to Files, Maniphest, Phriction and Differential.
  - Modified CSRF vaidator to use __csrf__.'x' and verified uploads and form
submissions don't work.

Reviewers: andrewjcg, aran, jungejason, tuomaspelkonen, erling
Commenters: andrewjcg, pedram
CC: aran, epriestley, andrewjcg, pedram
Differential Revision: 758

src/__celerity_resource_map__.php

@@ -738,7 +738,7 @@ celerity_register_resource_map(array(
   ),
   'javelin-behavior-refresh-csrf' =>
   array(
-    'uri' => '/res/39aa51f7/rsrc/js/application/core/behavior-refresh-csrf.js',
+    'uri' => '/res/a8204a73/rsrc/js/application/core/behavior-refresh-csrf.js',
     'type' => 'js',
     'requires' =>
     array(

src/aphront/request/AphrontRequest.php

@@ -117,15 +117,33 @@ class AphrontRequest {
     return $this->getExists(self::TYPE_AJAX);
   }
 
-  final public function isFormPost() {
-    $post = $this->getExists(self::TYPE_FORM) &&
-            $this->isHTTPPost();
+  public static function getCSRFTokenName() {
+    return '__csrf__';
+  }
 
-    if (!$post) {
-      return false;
+  public static function getCSRFHeaderName() {
+    return 'X-Phabricator-Csrf';
+  }
+
+  final public function validateCSRF() {
+    $token_name = self::getCSRFTokenName();
+    $token = $this->getStr($token_name);
+
+    // No token in the request, check the HTTP header which is added for Ajax
+    // requests.
+    if (empty($token)) {
+
+      // PHP mangles HTTP headers by uppercasing them and replacing hyphens with
+      // underscores, then prepending 'HTTP_'.
+      $php_index = self::getCSRFHeaderName();
+      $php_index = strtoupper($php_index);
+      $php_index = str_replace('-', '_', $php_index);
+      $php_index = 'HTTP_'.$php_index;
+
+      $token = idx($_SERVER, $php_index);
     }
 
-    $valid = $this->getUser()->validateCSRFToken($this->getStr('__csrf__'));
+    $valid = $this->getUser()->validateCSRFToken($token);
     if (!$valid) {
       // This should only be able to happen if you load a form, pull your
       // internet for 6 hours, and then reconnect and immediately submit,
@@ -143,6 +161,17 @@ class AphrontRequest {
     return true;
   }
 
+  final public function isFormPost() {
+    $post = $this->getExists(self::TYPE_FORM) &&
+            $this->isHTTPPost();
+
+    if (!$post) {
+      return false;
+    }
+
+    return $this->validateCSRF();
+  }
+
   final public function getCookie($name, $default = null) {
     return idx($_COOKIE, $name, $default);
   }

src/applications/files/controller/dropupload/PhabricatorFileDropUploadController.php

@@ -22,6 +22,9 @@ class PhabricatorFileDropUploadController extends PhabricatorFileController {
     $request = $this->getRequest();
     $user = $request->getUser();
 
+    // NOTE: Throws if valid CSRF token is not present in the request.
+    $request->validateCSRF();
+
     $data = file_get_contents('php://input');
     $name = $request->getStr('name');
 

src/infrastructure/javelin/markup/__init__.php

@@ -6,6 +6,7 @@
 
 
 
+phutil_require_module('phabricator', 'aphront/request');
 phutil_require_module('phabricator', 'infrastructure/celerity/api');
 
 phutil_require_module('phutil', 'markup');

src/infrastructure/javelin/markup/markup.php

@@ -56,7 +56,7 @@ function phabricator_render_form(PhabricatorUser $user, $attributes, $content) {
       'input',
       array(
         'type' => 'hidden',
-        'name' => '__csrf__',
+        'name' => AphrontRequest::getCSRFTokenName(),
         'value' => $user->getCSRFToken(),
       )).
     phutil_render_tag(

src/view/form/base/AphrontFormView.php

@@ -92,7 +92,7 @@ final class AphrontFormView extends AphrontView {
 
     $data = $this->data + array(
       '__form__' => 1,
-      '__csrf__' => $this->user->getCSRFToken(),
+      AphrontRequest::getCSRFTokenName() => $this->user->getCSRFToken(),
     );
     $inputs = array();
     foreach ($data as $key => $value) {

src/view/form/base/__init__.php

@@ -6,6 +6,7 @@
 
 
 
+phutil_require_module('phabricator', 'aphront/request');
 phutil_require_module('phabricator', 'infrastructure/celerity/api');
 phutil_require_module('phabricator', 'infrastructure/javelin/api');
 phutil_require_module('phabricator', 'infrastructure/javelin/markup');

src/view/page/standard/PhabricatorStandardPageView.php

@@ -121,8 +121,23 @@ class PhabricatorStandardPageView extends AphrontPageView {
     require_celerity_resource('phabricator-core-buttons-css');
     require_celerity_resource('phabricator-standard-page-view');
 
+    $current_token = null;
+    $request = $this->getRequest();
+    if ($request) {
+      $user = $request->getUser();
+      if ($user) {
+        $current_token = $user->getCSRFToken();
+      }
+    }
+
     Javelin::initBehavior('workflow', array());
-    Javelin::initBehavior('refresh-csrf', array());
+    Javelin::initBehavior(
+      'refresh-csrf',
+      array(
+        'tokenName' => AphrontRequest::getCSRFTokenName(),
+        'header'    => AphrontRequest::getCSRFHeaderName(),
+        'current'   => $current_token,
+      ));
     Javelin::initBehavior(
       'phabricator-keyboard-shortcuts',
       array(

src/view/page/standard/__init__.php

@@ -6,6 +6,7 @@
 
 
 
+phutil_require_module('phabricator', 'aphront/request');
 phutil_require_module('phabricator', 'applications/people/storage/preferences');
 phutil_require_module('phabricator', 'infrastructure/celerity/api');
 phutil_require_module('phabricator', 'infrastructure/env');

webroot/rsrc/js/application/core/behavior-refresh-csrf.js

@@ -27,18 +27,26 @@
  */
 JX.behavior('refresh-csrf', function(config) {
 
+  var current_token = config.current;
+
   function refresh_csrf() {
     new JX.Request('/login/refresh/', function(r) {
-        var inputs = JX.DOM.scry(document.body, 'input');
-        for (var ii = 0; ii < inputs.length; ii++) {
-          if (inputs[ii].name == '__csrf__') {
-            inputs[ii].value = r.token;
-          }
+      current_token = r.token;
+      var inputs = JX.DOM.scry(document.body, 'input');
+      for (var ii = 0; ii < inputs.length; ii++) {
+        if (inputs[ii].name == config.tokenName) {
+          inputs[ii].value = r.token;
         }
-      })
-      .send();
+      }
+    })
+    .send();
   }
 
   // Refresh the CSRF tokens every 55 minutes.
   setInterval(refresh_csrf, 1000 * 60 * 55);
+
+  // Additionally, add the CSRF token as an HTTP header to every AJAX request.
+  JX.Request.listen('open', function(r) {
+    r.getTransport().setRequestHeader(config.header, current_token);
+  });
 });