Fixed #19733 - deprecated ModelForms without 'fields' or 'exclude', and added '__all__' shortcut

This also updates all dependent functionality, including modelform_factory
 and modelformset_factory, and the generic views `ModelFormMixin`,
 `CreateView` and `UpdateView` which gain a new `fields` attribute.

docs/releases/1.6.txt

@@ -532,3 +532,55 @@ including it in an URLconf, simply replace::
 with::
 
     (r'^prefix/(?P<content_type_id>\d+)/(?P<object_id>.*)/$', 'django.contrib.contenttypes.views.shortcut'),
+
+``ModelForm`` without ``fields`` or ``exclude``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Previously, if you wanted a :class:`~django.forms.ModelForm` to use all fields on
+the model, you could simply omit the ``Meta.fields`` attribute, and all fields
+would be used.
+
+This can lead to security problems where fields are added to the model and,
+unintentionally, automatically become editable by end users. In some cases,
+particular with boolean fields, it is possible for this problem to be completely
+invisible. This is a form of `Mass assignment vulnerability
+<http://en.wikipedia.org/wiki/Mass_assignment_vulnerability>`_.
+
+For this reason, this behaviour is deprecated, and using the ``Meta.exclude``
+option is strongly discouraged. Instead, all fields that are intended for
+inclusion in the form should be listed explicitly in the ``fields`` attribute.
+
+If this security concern really does not apply in your case, there is a shortcut
+to explicitly indicate that all fields should be used - use the special value
+``"__all__"`` for the fields attribute::
+
+    class MyModelForm(ModelForm):
+        class Meta:
+            fields = "__all__"
+            model = MyModel
+
+If you have custom ``ModelForms`` that only need to be used in the admin, there
+is another option. The admin has its own methods for defining fields
+(``fieldsets`` etc.), and so adding a list of fields to the ``ModelForm`` is
+redundant. Instead, simply omit the ``Meta`` inner class of the ``ModelForm``,
+or omit the ``Meta.model`` attribute. Since the ``ModelAdmin`` subclass knows
+which model it is for, it can add the necessary attributes to derive a
+functioning ``ModelForm``. This behaviour also works for earlier Django
+versions.
+
+``UpdateView`` and ``CreateView`` without explicit fields
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The generic views :class:`~django.views.generic.edit.CreateView` and
+:class:`~django.views.generic.edit.UpdateView`, and anything else derived from
+:class:`~django.views.generic.edit.ModelFormMixin`, are vulnerable to the
+security problem described in the section above, because they can automatically
+create a ``ModelForm`` that uses all fields for a model.
+
+For this reason, if you use these views for editing models, you must also supply
+the ``fields`` attribute, which is a list of model fields and works in the same
+way as the :class:`~django.forms.ModelForm` ``Meta.fields`` attribute. Alternatively,
+you can set set the ``form_class`` attribute to a ``ModelForm`` that explicitly
+defines the fields to be used. Defining an ``UpdateView`` or ``CreateView``
+subclass to be used with a model but without an explicit list of fields is
+deprecated.