Fixed #11457: tightened the security check for "next" redirects after logins.

The new behavior still disallows redirects to off-site URLs, but now allows
redirects of the form `/some/other/view?foo=http://...`.

Thanks to brutasse.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@12635 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/contrib/auth/tests/views.py

@@ -1,8 +1,9 @@
 import os
 import re
+import urllib
 
 from django.conf import settings
-from django.contrib.auth import SESSION_KEY
+from django.contrib.auth import SESSION_KEY, REDIRECT_FIELD_NAME
 from django.contrib.auth.forms import AuthenticationForm
 from django.contrib.sites.models import Site, RequestSite
 from django.contrib.auth.models import User
@@ -183,6 +184,46 @@ class LoginTest(AuthViewsTestCase):
         self.assertEquals(response.context['site_name'], site.name)
         self.assert_(isinstance(response.context['form'], AuthenticationForm), 
                      'Login form is not an AuthenticationForm')
+
+    def test_security_check(self, password='password'):
+        login_url = reverse('django.contrib.auth.views.login')
+
+        # Those URLs should not pass the security check
+        for bad_url in ('http://example.com',
+                        'https://example.com',
+                        'ftp://exampel.com',
+                        '//example.com'):
+
+            nasty_url = '%(url)s?%(next)s=%(bad_url)s' % {
+                'url': login_url,
+                'next': REDIRECT_FIELD_NAME,
+                'bad_url': urllib.quote(bad_url)
+            }
+            response = self.client.post(nasty_url, {
+                'username': 'testclient',
+                'password': password,
+                }
+            )
+            self.assertEquals(response.status_code, 302)
+            self.assertFalse(bad_url in response['Location'], "%s should be blocked" % bad_url)
+
+        # Now, these URLs have an other URL as a GET parameter and therefore
+        # should be allowed
+        for url_ in ('http://example.com', 'https://example.com',
+                    'ftp://exampel.com',  '//example.com'):
+            safe_url = '%(url)s?%(next)s=/view/?param=%(safe_param)s' % {
+                'url': login_url,
+                'next': REDIRECT_FIELD_NAME,
+                'safe_param': urllib.quote(url_)
+            }
+            response = self.client.post(safe_url, {
+                    'username': 'testclient',
+                    'password': password,
+                }
+            )
+            self.assertEquals(response.status_code, 302)
+            self.assertTrue('/view/?param=%s' % url_ in response['Location'], "/view/?param=%s should be allowed" % url_)
+
         
 class LogoutTest(AuthViewsTestCase):
     urls = 'django.contrib.auth.tests.urls'

django/contrib/auth/views.py

@@ -1,5 +1,8 @@
+import re
 from django.conf import settings
 from django.contrib.auth import REDIRECT_FIELD_NAME
+# Avoid shadowing the login() view below.
+from django.contrib.auth import login as auth_login
 from django.contrib.auth.decorators import login_required
 from django.contrib.auth.forms import AuthenticationForm
 from django.contrib.auth.forms import PasswordResetForm, SetPasswordForm, PasswordChangeForm
@@ -20,26 +23,42 @@ from django.views.decorators.cache import never_cache
 def login(request, template_name='registration/login.html',
           redirect_field_name=REDIRECT_FIELD_NAME,
           authentication_form=AuthenticationForm):
-    "Displays the login form and handles the login action."
+    """Displays the login form and handles the login action."""
+
     redirect_to = request.REQUEST.get(redirect_field_name, '')
+    
     if request.method == "POST":
         form = authentication_form(data=request.POST)
         if form.is_valid():
             # Light security check -- make sure redirect_to isn't garbage.
-            if not redirect_to or '//' in redirect_to or ' ' in redirect_to:
+            if not redirect_to or ' ' in redirect_to:
                 redirect_to = settings.LOGIN_REDIRECT_URL
-            from django.contrib.auth import login
-            login(request, form.get_user())
+            
+            # Heavier security check -- redirects to http://example.com should 
+            # not be allowed, but things like /view/?param=http://example.com 
+            # should be allowed. This regex checks if there is a '//' *before* a
+            # question mark.
+            elif '//' in redirect_to and re.match(r'[^\?]*//', redirect_to):
+                    redirect_to = settings.LOGIN_REDIRECT_URL
+            
+            # Okay, security checks complete. Log the user in.
+            auth_login(request, form.get_user())
+
             if request.session.test_cookie_worked():
                 request.session.delete_test_cookie()
+
             return HttpResponseRedirect(redirect_to)
+
     else:
         form = authentication_form(request)
+    
     request.session.set_test_cookie()
+    
     if Site._meta.installed:
         current_site = Site.objects.get_current()
     else:
         current_site = RequestSite(request)
+    
     return render_to_response(template_name, {
         'form': form,
         redirect_field_name: redirect_to,