[1.11.x] Fixed #28488 -- Reallowed error handlers to access CSRF tokens.

Regression in eef95ea96faef0b7dbbe0c8092202b74f68a899b.

Backport of c4c128d67c7dc2830631c6859a204c9d259f1fb1 from master

5 files changed, 57 insertions, 6 deletions

diff --git a/django/middleware/csrf.py b/django/middleware/csrf.py
index d7359e4912..13134309a5 100644
--- a/django/middleware/csrf.py
+++ b/django/middleware/csrf.py
@@ -201,15 +201,16 @@ class CsrfViewMiddleware(MiddlewareMixin):
             # Set the Vary header since content varies with the CSRF cookie.
             patch_vary_headers(response, ('Cookie',))
 
-    def process_view(self, request, callback, callback_args, callback_kwargs):
-        if getattr(request, 'csrf_processing_done', False):
-            return None
-
+    def process_request(self, request):
         csrf_token = self._get_token(request)
         if csrf_token is not None:
             # Use same token next time.
             request.META['CSRF_COOKIE'] = csrf_token
 
+    def process_view(self, request, callback, callback_args, callback_kwargs):
+        if getattr(request, 'csrf_processing_done', False):
+            return None
+
         # Wait until request.META["CSRF_COOKIE"] has been manipulated before
         # bailing out, so that get_token still works
         if getattr(callback, 'csrf_exempt', False):
@@ -285,6 +286,7 @@ class CsrfViewMiddleware(MiddlewareMixin):
                     reason = REASON_BAD_REFERER % referer.geturl()
                     return self._reject(request, reason)
 
+            csrf_token = request.META.get('CSRF_COOKIE')
             if csrf_token is None:
                 # No CSRF cookie. For POST requests, we insist on a CSRF cookie,
                 # and in this way we can avoid all CSRF attacks, including login
diff --git a/docs/releases/1.11.6.txt b/docs/releases/1.11.6.txt
index ff9d4385fe..222a9c9125 100644
--- a/docs/releases/1.11.6.txt
+++ b/docs/releases/1.11.6.txt
@@ -14,3 +14,7 @@ Bugfixes
 
 * Fixed crash when using the name of a model's autogenerated primary key
   (``id``) in an ``Index``'s ``fields`` (:ticket:`28597`).
+
+* Fixed a regression in Django 1.9 where a custom view error handler such as
+  ``handler404`` that accesses ``csrf_token`` could cause CSRF verification
+  failures on other pages (:ticket:`28488`).
diff --git a/tests/csrf_tests/csrf_token_error_handler_urls.py b/tests/csrf_tests/csrf_token_error_handler_urls.py
new file mode 100644
index 0000000000..3c02f613ec
--- /dev/null
+++ b/tests/csrf_tests/csrf_token_error_handler_urls.py
@@ -0,0 +1,3 @@
+urlpatterns = []
+
+handler404 = 'csrf_tests.views.csrf_token_error_handler'
diff --git a/tests/csrf_tests/tests.py b/tests/csrf_tests/tests.py
index e71fb40193..306a4fff33 100644
--- a/tests/csrf_tests/tests.py
+++ b/tests/csrf_tests/tests.py
@@ -90,6 +90,7 @@ class CsrfViewMiddlewareTestMixin(object):
         # does use the csrf request processor.  By using this, we are testing
         # that the view processor is properly lazy and doesn't call get_token()
         # until needed.
+        self.mw.process_request(req)
         self.mw.process_view(req, non_token_view_using_request_processor, (), {})
         resp = non_token_view_using_request_processor(req)
         resp2 = self.mw.process_response(req, resp)
@@ -105,6 +106,7 @@ class CsrfViewMiddlewareTestMixin(object):
         """
         with patch_logger('django.security.csrf', 'warning') as logger_calls:
             req = self._get_POST_no_csrf_cookie_request()
+            self.mw.process_request(req)
             req2 = self.mw.process_view(req, post_form_view, (), {})
             self.assertEqual(403, req2.status_code)
             self.assertEqual(logger_calls[0], 'Forbidden (%s): ' % REASON_NO_CSRF_COOKIE)
@@ -116,6 +118,7 @@ class CsrfViewMiddlewareTestMixin(object):
         """
         with patch_logger('django.security.csrf', 'warning') as logger_calls:
             req = self._get_POST_csrf_cookie_request()
+            self.mw.process_request(req)
             req2 = self.mw.process_view(req, post_form_view, (), {})
             self.assertEqual(403, req2.status_code)
             self.assertEqual(logger_calls[0], 'Forbidden (%s): ' % REASON_BAD_TOKEN)
@@ -125,6 +128,7 @@ class CsrfViewMiddlewareTestMixin(object):
         If both a cookie and a token is present, the middleware lets it through.
         """
         req = self._get_POST_request_with_token()
+        self.mw.process_request(req)
         req2 = self.mw.process_view(req, post_form_view, (), {})
         self.assertIsNone(req2)
 
@@ -134,6 +138,7 @@ class CsrfViewMiddlewareTestMixin(object):
         has been applied to the view, the middleware lets it through
         """
         req = self._get_POST_csrf_cookie_request()
+        self.mw.process_request(req)
         req2 = self.mw.process_view(req, csrf_exempt(post_form_view), (), {})
         self.assertIsNone(req2)
 
@@ -143,6 +148,7 @@ class CsrfViewMiddlewareTestMixin(object):
         """
         req = self._get_POST_csrf_cookie_request()
         req.META['HTTP_X_CSRFTOKEN'] = self._csrf_id
+        self.mw.process_request(req)
         req2 = self.mw.process_view(req, post_form_view, (), {})
         self.assertIsNone(req2)
 
@@ -153,6 +159,7 @@ class CsrfViewMiddlewareTestMixin(object):
         """
         req = self._get_POST_csrf_cookie_request()
         req.META['HTTP_X_CSRFTOKEN_CUSTOMIZED'] = self._csrf_id
+        self.mw.process_request(req)
         req2 = self.mw.process_view(req, post_form_view, (), {})
         self.assertIsNone(req2)
 
@@ -181,12 +188,14 @@ class CsrfViewMiddlewareTestMixin(object):
         req = self._get_GET_csrf_cookie_request()
         req.method = 'PUT'
         req.META['HTTP_X_CSRFTOKEN'] = self._csrf_id
+        self.mw.process_request(req)
         req2 = self.mw.process_view(req, post_form_view, (), {})
         self.assertIsNone(req2)
 
         req = self._get_GET_csrf_cookie_request()
         req.method = 'DELETE'
         req.META['HTTP_X_CSRFTOKEN'] = self._csrf_id
+        self.mw.process_request(req)
         req2 = self.mw.process_view(req, post_form_view, (), {})
         self.assertIsNone(req2)
 
@@ -220,6 +229,7 @@ class CsrfViewMiddlewareTestMixin(object):
         CsrfTokenNode works when a CSRF cookie is set.
         """
         req = self._get_GET_csrf_cookie_request()
+        self.mw.process_request(req)
         self.mw.process_view(req, token_view, (), {})
         resp = token_view(req)
         self._check_token_present(resp)
@@ -229,6 +239,7 @@ class CsrfViewMiddlewareTestMixin(object):
         get_token still works for a view decorated with 'csrf_exempt'.
         """
         req = self._get_GET_csrf_cookie_request()
+        self.mw.process_request(req)
         self.mw.process_view(req, csrf_exempt(token_view), (), {})
         resp = token_view(req)
         self._check_token_present(resp)
@@ -260,6 +271,7 @@ class CsrfViewMiddlewareTestMixin(object):
         requests. If it appears in the response, it should keep its value.
         """
         req = self._get_POST_request_with_token()
+        self.mw.process_request(req)
         self.mw.process_view(req, token_view, (), {})
         resp = token_view(req)
         resp = self.mw.process_response(req, resp)
@@ -333,6 +345,7 @@ class CsrfViewMiddlewareTestMixin(object):
         req._is_secure_override = True
         req.META['HTTP_HOST'] = 'www.example.com'
         req.META['HTTP_REFERER'] = 'https://www.example.com/somepage'
+        self.mw.process_request(req)
         req2 = self.mw.process_view(req, post_form_view, (), {})
         self.assertIsNone(req2)
 
@@ -347,6 +360,7 @@ class CsrfViewMiddlewareTestMixin(object):
         req._is_secure_override = True
         req.META['HTTP_HOST'] = 'www.example.com'
         req.META['HTTP_REFERER'] = 'https://www.example.com'
+        self.mw.process_request(req)
         req2 = self.mw.process_view(req, post_form_view, (), {})
         self.assertIsNone(req2)
 
@@ -360,6 +374,7 @@ class CsrfViewMiddlewareTestMixin(object):
             'HTTP_X_FORWARDED_HOST': 'www.example.com',
             'HTTP_X_FORWARDED_PORT': '443',
         })
+        self.mw.process_request(req)
         req2 = self.mw.process_view(req, post_form_view, (), {})
         self.assertIsNone(req2)
 
@@ -373,6 +388,7 @@ class CsrfViewMiddlewareTestMixin(object):
         req._is_secure_override = True
         req.META['HTTP_HOST'] = 'www.example.com'
         req.META['HTTP_REFERER'] = 'https://dashboard.example.com'
+        self.mw.process_request(req)
         req2 = self.mw.process_view(req, post_form_view, (), {})
         self.assertIsNone(req2)
 
@@ -386,6 +402,7 @@ class CsrfViewMiddlewareTestMixin(object):
         req._is_secure_override = True
         req.META['HTTP_HOST'] = 'www.example.com'
         req.META['HTTP_REFERER'] = 'https://dashboard.example.com'
+        self.mw.process_request(req)
         response = self.mw.process_view(req, post_form_view, (), {})
         self.assertIsNone(response)
 
@@ -394,6 +411,7 @@ class CsrfViewMiddlewareTestMixin(object):
         req._is_secure_override = True
         req.META['HTTP_REFERER'] = 'https://foo.example.com/'
         req.META['SERVER_PORT'] = '443'
+        self.mw.process_request(req)
         response = self.mw.process_view(req, post_form_view, (), {})
         self.assertIsNone(response)
 
@@ -403,6 +421,7 @@ class CsrfViewMiddlewareTestMixin(object):
         req.META['HTTP_HOST'] = 'www.example.com'
         req.META['HTTP_REFERER'] = 'https://foo.example.com:4443/'
         req.META['SERVER_PORT'] = '4443'
+        self.mw.process_request(req)
         response = self.mw.process_view(req, post_form_view, (), {})
         self.assertIsNone(response)
 
@@ -467,11 +486,13 @@ class CsrfViewMiddlewareTestMixin(object):
         token = ('ABC' + self._csrf_id)[:CSRF_TOKEN_LENGTH]
 
         req = CsrfPostRequest(token, raise_error=False)
+        self.mw.process_request(req)
         resp = self.mw.process_view(req, post_form_view, (), {})
         self.assertIsNone(resp)
 
         req = CsrfPostRequest(token, raise_error=True)
         with patch_logger('django.security.csrf', 'warning') as logger_calls:
+            self.mw.process_request(req)
             resp = self.mw.process_view(req, post_form_view, (), {})
             self.assertEqual(resp.status_code, 403)
             self.assertEqual(logger_calls[0], 'Forbidden (%s): ' % REASON_BAD_TOKEN)
@@ -609,6 +630,7 @@ class CsrfViewMiddlewareTests(CsrfViewMiddlewareTestMixin, SimpleTestCase):
         The csrf token is reset from a bare secret.
         """
         req = self._get_POST_bare_secret_csrf_cookie_request_with_token()
+        self.mw.process_request(req)
         req2 = self.mw.process_view(req, token_view, (), {})
         self.assertIsNone(req2)
         resp = token_view(req)
@@ -680,7 +702,7 @@ class CsrfViewMiddlewareUseSessionsTests(CsrfViewMiddlewareTestMixin, SimpleTest
             'SessionMiddleware must appear before CsrfViewMiddleware in MIDDLEWARE.'
         )
         with self.assertRaisesMessage(ImproperlyConfigured, msg):
-            self.mw.process_view(HttpRequest(), None, (), {})
+            self.mw.process_request(HttpRequest())
 
     def test_process_response_get_token_used(self):
         """The ensure_csrf_cookie() decorator works without middleware."""
@@ -754,3 +776,16 @@ class CsrfViewMiddlewareUseSessionsTests(CsrfViewMiddlewareTestMixin, SimpleTest
             'Referer checking failed - Referer is insecure while host is secure.',
             status_code=403,
         )
+
+
+@override_settings(ROOT_URLCONF='csrf_tests.csrf_token_error_handler_urls', DEBUG=False)
+class CsrfInErrorHandlingViewsTests(SimpleTestCase):
+    def test_csrf_token_on_404_stays_constant(self):
+        response = self.client.get('/does not exist/')
+        # The error handler returns status code 599.
+        self.assertEqual(response.status_code, 599)
+        token1 = response.content
+        response = self.client.get('/does not exist/')
+        self.assertEqual(response.status_code, 599)
+        token2 = response.content
+        self.assertTrue(equivalent_tokens(token1.decode('ascii'), token2.decode('ascii')))
diff --git a/tests/csrf_tests/views.py b/tests/csrf_tests/views.py
index e41f2d0805..cf1b67fc27 100644
--- a/tests/csrf_tests/views.py
+++ b/tests/csrf_tests/views.py
@@ -1,7 +1,8 @@
 from __future__ import unicode_literals
 
 from django.http import HttpResponse
-from django.template import RequestContext, Template
+from django.middleware.csrf import get_token
+from django.template import Context, RequestContext, Template
 from django.template.context_processors import csrf
 from django.views.decorators.csrf import ensure_csrf_cookie
 
@@ -30,3 +31,9 @@ def non_token_view_using_request_processor(request):
     context = RequestContext(request, processors=[csrf])
     template = Template('')
     return HttpResponse(template.render(context))
+
+
+def csrf_token_error_handler(request, **kwargs):
+    """This error handler accesses the CSRF token."""
+    template = Template(get_token(request))
+    return HttpResponse(template.render(Context()), status=599)