When viewing raw file content in Differential, cache it into the File tool

before displaying it

Summary:
@alok reported a vulnerability where Flash will run carefully-crafted plain text
files.

When the user requests a raw file, cache it into Files if it isn't already
there. Then redirect them to Files. This solves the problem by executing the
SWF/TXT with CDN-domain permissions, not content-domain permissions, provided
the install is correctly configured. (Followup diff coming to make this more
universally true.)

NOTE: We'll still show raw data in Diffusion. The barrier to XSS here is much
higher (you need commit access) but I'll do something similar there. We aren't
vulnerable in Paste, since we already use Files.

Test Plan: Clicked "View Old File", "View New File" in an alt-domain
configuration, got redirected to a cookie-free domain before being delivered the
response.

Reviewers: btrahan, alok

Reviewed By: btrahan

CC: aran, epriestley

Differential Revision: https://secure.phabricator.com/D1607

src/applications/differential/controller/changesetview/DifferentialChangesetViewController.php

@@ -54,9 +54,9 @@ class DifferentialChangesetViewController extends DifferentialController {
       }
       switch ($view) {
         case 'new':
-          return $this->buildRawFileResponse($changeset->makeNewFile());
+          return $this->buildRawFileResponse($changeset, $is_new = true);
         case 'old':
-          return $this->buildRawFileResponse($changeset->makeOldFile());
+          return $this->buildRawFileResponse($changeset, $is_new = false);
         default:
           return new Aphront400Response();
       }
@@ -256,10 +256,53 @@ class DifferentialChangesetViewController extends DifferentialController {
       $author_phid);
   }
 
-  private function buildRawFileResponse($text) {
+  private function buildRawFileResponse(
-    return id(new AphrontFileResponse())
+    DifferentialChangeset $changeset,
-      ->setMimeType('text/plain')
+    $is_new) {
-      ->setContent($text);
+
+    if ($is_new) {
+      $key = 'raw:new:phid';
+    } else {
+      $key = 'raw:old:phid';
+    }
+
+    $metadata = $changeset->getMetadata();
+
+    $file = null;
+    $phid = idx($metadata, $key);
+    if ($phid) {
+      $file = id(new PhabricatorFile())->loadOneWhere(
+        'phid = %s',
+        $phid);
+    }
+
+    if (!$file) {
+      // This is just building a cache of the changeset content in the file
+      // tool, and is safe to run on a read pathway.
+      $unguard = AphrontWriteGuard::beginScopedUnguardedWrites();
+
+      if ($is_new) {
+        $data = $changeset->makeNewFile();
+      } else {
+        $data = $changeset->makeOldFile();
+      }
+
+      $file = PhabricatorFile::newFromFileData(
+        $data,
+        array(
+          'name'      => $changeset->getFilename(),
+          'mime-type' => 'text/plain',
+        ));
+
+      $metadata[$key] = $file->getPHID();
+      $changeset->setMetadata($metadata);
+      $changeset->save();
+
+      unset($unguard);
+    }
+
+    return id(new AphrontRedirectResponse())
+      ->setURI($file->getBestURI());
   }
 
   private function buildLintInlineComments($changeset) {

src/applications/differential/controller/changesetview/__init__.php

@@ -11,8 +11,8 @@ phutil_require_module('arcanist', 'unit/result');
 phutil_require_module('phabricator', 'aphront/response/400');
 phutil_require_module('phabricator', 'aphront/response/404');
 phutil_require_module('phabricator', 'aphront/response/ajax');
-phutil_require_module('phabricator', 'aphront/response/file');
 phutil_require_module('phabricator', 'aphront/response/redirect');
+phutil_require_module('phabricator', 'aphront/writeguard');
 phutil_require_module('phabricator', 'applications/differential/controller/base');
 phutil_require_module('phabricator', 'applications/differential/parser/changeset');
 phutil_require_module('phabricator', 'applications/differential/storage/changeset');
@@ -20,6 +20,7 @@ phutil_require_module('phabricator', 'applications/differential/storage/diffprop
 phutil_require_module('phabricator', 'applications/differential/storage/inlinecomment');
 phutil_require_module('phabricator', 'applications/differential/view/changesetdetailview');
 phutil_require_module('phabricator', 'applications/differential/view/primarypane');
+phutil_require_module('phabricator', 'applications/files/storage/file');
 phutil_require_module('phabricator', 'applications/markup/engine');
 phutil_require_module('phabricator', 'applications/phid/handle/data');
 phutil_require_module('phabricator', 'infrastructure/diff/engine');