[1.4.x] Prevented views.static.serve() from using large memory on large files.

This is a security fix. Disclosure following shortly.

django/views/static.py

@@ -16,6 +16,9 @@ from django.template import loader, Template, Context, TemplateDoesNotExist
 from django.utils.http import http_date, parse_http_date
 from django.utils.translation import ugettext as _, ugettext_noop
 
+STREAM_CHUNK_SIZE = 4096
+
+
 def serve(request, path, document_root=None, show_indexes=False):
     """
     Serve static files below a given point in the directory structure.
@@ -59,8 +62,8 @@ def serve(request, path, document_root=None, show_indexes=False):
     if not was_modified_since(request.META.get('HTTP_IF_MODIFIED_SINCE'),
                               statobj.st_mtime, statobj.st_size):
         return HttpResponseNotModified(mimetype=mimetype)
-    with open(fullpath, 'rb') as f:
-        response = HttpResponse(f.read(), mimetype=mimetype)
+    f = open(fullpath, 'rb')
+    response = HttpResponse(iter(lambda: f.read(STREAM_CHUNK_SIZE), ''), mimetype=mimetype)
     response["Last-Modified"] = http_date(statobj.st_mtime)
     if stat.S_ISREG(statobj.st_mode):
         response["Content-Length"] = statobj.st_size

docs/releases/1.4.18.txt

@@ -45,6 +45,21 @@ from a XSS attack. This bug doesn't affect Django currently, since we only put
 this URL into the ``Location`` response header and browsers seem to ignore
 JavaScript there.
 
+Denial-of-service attack against ``django.views.static.serve``
+==============================================================
+
+In older versions of Django, the :func:`django.views.static.serve` view read
+the files it served one line at a time. Therefore, a big file with no newlines
+would result in memory usage equal to the size of that file. An attacker could
+exploit this and launch a denial-of-service attack by simultaneously requesting
+many large files. This view now reads the file in chunks to prevent large
+memory usage.
+
+Note, however, that this view has always carried a warning that it is not
+hardened for production use and should be used only as a development aid. Now
+may be a good time to audit your project and serve your files in production
+using a real front-end web server if you are not doing so.
+
 Bugfixes
 ========
 

tests/regressiontests/views/tests/static.py

@@ -7,6 +7,7 @@ from django.conf import settings
 from django.conf.urls.static import static
 from django.test import TestCase
 from django.http import HttpResponseNotModified
+from django.views.static import STREAM_CHUNK_SIZE
 
 from .. import urls
 from ..urls import media_dir
@@ -29,10 +30,19 @@ class StaticTests(TestCase):
         for filename in media_files:
             response = self.client.get('/views/%s/%s' % (self.prefix, filename))
             file_path = path.join(media_dir, filename)
-            self.assertEqual(open(file_path).read(), response.content)
-            self.assertEqual(len(response.content), int(response['Content-Length']))
+            content = response.content
+            self.assertEqual(open(file_path).read(), content)
+            self.assertEqual(len(content), int(response['Content-Length']))
             self.assertEqual(mimetypes.guess_type(file_path)[1], response.get('Content-Encoding', None))
 
+    def test_chunked(self):
+        "The static view should stream files in chunks to avoid large memory usage"
+        response = self.client.get('/views/%s/%s' % (self.prefix, 'long-line.txt'))
+        first_chunk = iter(response).next()
+        self.assertEqual(len(first_chunk), STREAM_CHUNK_SIZE)
+        second_chunk = response.next()
+        self.assertEqual(len(second_chunk), 1451)
+
     def test_unknown_mime_type(self):
         response = self.client.get('/views/%s/file.unknown' % self.prefix)
         self.assertEqual('application/octet-stream', response['Content-Type'])
@@ -71,9 +81,9 @@ class StaticTests(TestCase):
         response = self.client.get('/views/%s/%s' % (self.prefix, file_name),
                                    HTTP_IF_MODIFIED_SINCE=invalid_date)
         file = open(path.join(media_dir, file_name))
-        self.assertEqual(file.read(), response.content)
-        self.assertEqual(len(response.content),
-                          int(response['Content-Length']))
+        content = response.content
+        self.assertEqual(file.read(), content)
+        self.assertEqual(len(content), int(response['Content-Length']))
 
     def test_invalid_if_modified_since2(self):
         """Handle even more bogus If-Modified-Since values gracefully
@@ -86,9 +96,9 @@ class StaticTests(TestCase):
         response = self.client.get('/views/%s/%s' % (self.prefix, file_name),
                                    HTTP_IF_MODIFIED_SINCE=invalid_date)
         file = open(path.join(media_dir, file_name))
-        self.assertEqual(file.read(), response.content)
-        self.assertEqual(len(response.content),
-                          int(response['Content-Length']))
+        content = response.content
+        self.assertEqual(file.read(), content)
+        self.assertEqual(len(content), int(response['Content-Length']))
 
 
 class StaticHelperTest(StaticTests):