[1.10.x] Fixed #27363 -- Replaced unsafe redirect in SessionMiddleware with SuspiciousOperation.

Backport of 1ce04bcce0 from master

django/contrib/sessions/middleware.py

@@ -3,7 +3,7 @@ from importlib import import_module
 
 from django.conf import settings
 from django.contrib.sessions.backends.base import UpdateError
-from django.shortcuts import redirect
+from django.core.exceptions import SuspiciousOperation
 from django.utils.cache import patch_vary_headers
 from django.utils.deprecation import MiddlewareMixin
 from django.utils.http import cookie_date
@@ -57,10 +57,11 @@ class SessionMiddleware(MiddlewareMixin):
                         try:
                             request.session.save()
                         except UpdateError:
-                            # The user is now logged out; redirecting to same
-                            # page will result in a redirect to the login page
-                            # if required.
-                            return redirect(request.path)
+                            raise SuspiciousOperation(
+                                "The request's session was deleted before the "
+                                "request completed. The user may have logged "
+                                "out in a concurrent request, for example."
+                            )
                         response.set_cookie(
                             settings.SESSION_COOKIE_NAME,
                             request.session.session_key, max_age=max_age,

docs/releases/1.10.3.txt

@@ -26,3 +26,7 @@ Bugfixes
 
 * Prevented ``i18n_patterns()`` from using too much of the URL as the language
   to fix a use case for ``prefix_default_language=False`` (:ticket:`27063`).
+
+* Replaced a possibly incorrect redirect from ``SessionMiddleware`` when a
+  session is destroyed in a concurrent request with a ``SuspiciousOperation``
+  to indicate that the request can't be completed (:ticket:`27363`).

tests/sessions_tests/tests.py

@@ -25,7 +25,7 @@ from django.contrib.sessions.serializers import (
 from django.core import management
 from django.core.cache import caches
 from django.core.cache.backends.base import InvalidCacheBackendError
-from django.core.exceptions import ImproperlyConfigured
+from django.core.exceptions import ImproperlyConfigured, SuspiciousOperation
 from django.http import HttpResponse
 from django.test import (
     RequestFactory, TestCase, ignore_warnings, override_settings,
@@ -704,14 +704,15 @@ class SessionMiddlewareTests(TestCase):
         request.session.save(must_create=True)
         request.session.delete()
 
-        # Handle the response through the middleware. It will try to save the
-        # deleted session which will cause an UpdateError that's caught and
-        # results in a redirect to the original page.
-        response = middleware.process_response(request, response)
-
-        # Check that the response is a redirect.
-        self.assertEqual(response.status_code, 302)
-        self.assertEqual(response['Location'], path)
+        msg = (
+            "The request's session was deleted before the request completed. "
+            "The user may have logged out in a concurrent request, for example."
+        )
+        with self.assertRaisesMessage(SuspiciousOperation, msg):
+            # Handle the response through the middleware. It will try to save
+            # the deleted session which will cause an UpdateError that's caught
+            # and raised as a SuspiciousOperation.
+            middleware.process_response(request, response)
 
     def test_session_delete_on_end(self):
         request = RequestFactory().get('/')