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Added a default limit to the maximum number of forms in a formset.

This is a security fix. Disclosure and advisory coming shortly.
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commit 35c991aa06aa34fa458f01eac49275ff4c2d76f9 1 parent 1f39eaf
@aaugustin aaugustin authored carljm committed
View
23 django/forms/formsets.py
@@ -21,6 +21,9 @@
ORDERING_FIELD_NAME = 'ORDER'
DELETION_FIELD_NAME = 'DELETE'
+# default maximum number of forms in a formset, to prevent memory exhaustion
+DEFAULT_MAX_NUM = 1000
+
class ManagementForm(Form):
"""
``ManagementForm`` is used to keep track of how many form instances
@@ -97,11 +100,10 @@ def total_form_count(self):
total_forms = initial_forms + self.extra
# Allow all existing related objects/inlines to be displayed,
# but don't allow extra beyond max_num.
- if self.max_num is not None:
- if initial_forms > self.max_num >= 0:
- total_forms = initial_forms
- elif total_forms > self.max_num >= 0:
- total_forms = self.max_num
+ if initial_forms > self.max_num >= 0:
+ total_forms = initial_forms
+ elif total_forms > self.max_num >= 0:
+ total_forms = self.max_num
return total_forms
def initial_form_count(self):
@@ -111,14 +113,14 @@ def initial_form_count(self):
else:
# Use the length of the inital data if it's there, 0 otherwise.
initial_forms = self.initial and len(self.initial) or 0
- if self.max_num is not None and (initial_forms > self.max_num >= 0):
+ if initial_forms > self.max_num >= 0:
initial_forms = self.max_num
return initial_forms
def _construct_forms(self):
# instantiate all the forms and put them in self.forms
self.forms = []
- for i in xrange(self.total_form_count()):
+ for i in xrange(min(self.total_form_count(), self.absolute_max)):
self.forms.append(self._construct_form(i))
def _construct_form(self, i, **kwargs):
@@ -367,9 +369,14 @@ def as_ul(self):
def formset_factory(form, formset=BaseFormSet, extra=1, can_order=False,
can_delete=False, max_num=None):
"""Return a FormSet for the given form class."""
+ if max_num is None:
+ max_num = DEFAULT_MAX_NUM
+ # hard limit on forms instantiated, to prevent memory-exhaustion attacks
+ # limit defaults to DEFAULT_MAX_NUM, but developer can increase it via max_num
+ absolute_max = max(DEFAULT_MAX_NUM, max_num)
attrs = {'form': form, 'extra': extra,
'can_order': can_order, 'can_delete': can_delete,
- 'max_num': max_num}
+ 'max_num': max_num, 'absolute_max': absolute_max}
return type(form.__name__ + str('FormSet'), (formset,), attrs)
def all_valid(formsets):
View
4 docs/topics/forms/formsets.txt
@@ -98,8 +98,8 @@ If the value of ``max_num`` is greater than the number of existing
objects, up to ``extra`` additional blank forms will be added to the formset,
so long as the total number of forms does not exceed ``max_num``.
-A ``max_num`` value of ``None`` (the default) puts no limit on the number of
-forms displayed.
+A ``max_num`` value of ``None`` (the default) puts a high limit on the number
+of forms displayed (1000). In practice this is equivalent to no limit.
Formset validation
------------------
View
4 docs/topics/forms/modelforms.txt
@@ -738,8 +738,8 @@ so long as the total number of forms does not exceed ``max_num``::
<tr><th><label for="id_form-2-name">Name:</label></th><td><input id="id_form-2-name" type="text" name="form-2-name" value="Walt Whitman" maxlength="100" /><input type="hidden" name="form-2-id" value="2" id="id_form-2-id" /></td></tr>
<tr><th><label for="id_form-3-name">Name:</label></th><td><input id="id_form-3-name" type="text" name="form-3-name" maxlength="100" /><input type="hidden" name="form-3-id" id="id_form-3-id" /></td></tr>
-A ``max_num`` value of ``None`` (the default) puts no limit on the number of
-forms displayed.
+A ``max_num`` value of ``None`` (the default) puts a high limit on the number
+of forms displayed (1000). In practice this is equivalent to no limit.
Using a model formset in a view
-------------------------------
View
70 tests/regressiontests/forms/tests/formsets.py
@@ -2,7 +2,7 @@
from __future__ import unicode_literals
from django.forms import (CharField, DateField, FileField, Form, IntegerField,
- ValidationError)
+ ValidationError, formsets)
from django.forms.formsets import BaseFormSet, formset_factory
from django.forms.util import ErrorList
from django.test import TestCase
@@ -51,7 +51,7 @@ def test_basic_formset(self):
# for adding data. By default, it displays 1 blank form. It can display more,
# but we'll look at how to do so later.
formset = ChoiceFormSet(auto_id=False, prefix='choices')
- self.assertHTMLEqual(str(formset), """<input type="hidden" name="choices-TOTAL_FORMS" value="1" /><input type="hidden" name="choices-INITIAL_FORMS" value="0" /><input type="hidden" name="choices-MAX_NUM_FORMS" />
+ self.assertHTMLEqual(str(formset), """<input type="hidden" name="choices-TOTAL_FORMS" value="1" /><input type="hidden" name="choices-INITIAL_FORMS" value="0" /><input type="hidden" name="choices-MAX_NUM_FORMS" value="1000" />
<tr><th>Choice:</th><td><input type="text" name="choices-0-choice" /></td></tr>
<tr><th>Votes:</th><td><input type="text" name="choices-0-votes" /></td></tr>""")
@@ -654,8 +654,8 @@ def test_limiting_max_forms(self):
# Limiting the maximum number of forms ########################################
# Base case for max_num.
- # When not passed, max_num will take its default value of None, i.e. unlimited
- # number of forms, only controlled by the value of the extra parameter.
+ # When not passed, max_num will take a high default value, leaving the
+ # number of forms only controlled by the value of the extra parameter.
LimitedFavoriteDrinkFormSet = formset_factory(FavoriteDrinkForm, extra=3)
formset = LimitedFavoriteDrinkFormSet()
@@ -702,8 +702,8 @@ def test_limiting_max_forms(self):
def test_max_num_with_initial_data(self):
# max_num with initial data
- # When not passed, max_num will take its default value of None, i.e. unlimited
- # number of forms, only controlled by the values of the initial and extra
+ # When not passed, max_num will take a high default value, leaving the
+ # number of forms only controlled by the value of the initial and extra
# parameters.
initial = [
@@ -878,6 +878,64 @@ def is_valid(self):
self.assertTrue(formset.is_valid())
self.assertTrue(all([form.is_valid_called for form in formset.forms]))
+ def test_hard_limit_on_instantiated_forms(self):
+ """A formset has a hard limit on the number of forms instantiated."""
+ # reduce the default limit of 1000 temporarily for testing
+ _old_DEFAULT_MAX_NUM = formsets.DEFAULT_MAX_NUM
+ try:
+ formsets.DEFAULT_MAX_NUM = 3
+ ChoiceFormSet = formset_factory(Choice)
+ # someone fiddles with the mgmt form data...
+ formset = ChoiceFormSet(
+ {
+ 'choices-TOTAL_FORMS': '4',
+ 'choices-INITIAL_FORMS': '0',
+ 'choices-MAX_NUM_FORMS': '4',
+ 'choices-0-choice': 'Zero',
+ 'choices-0-votes': '0',
+ 'choices-1-choice': 'One',
+ 'choices-1-votes': '1',
+ 'choices-2-choice': 'Two',
+ 'choices-2-votes': '2',
+ 'choices-3-choice': 'Three',
+ 'choices-3-votes': '3',
+ },
+ prefix='choices',
+ )
+ # But we still only instantiate 3 forms
+ self.assertEqual(len(formset.forms), 3)
+ finally:
+ formsets.DEFAULT_MAX_NUM = _old_DEFAULT_MAX_NUM
+
+ def test_increase_hard_limit(self):
+ """Can increase the built-in forms limit via a higher max_num."""
+ # reduce the default limit of 1000 temporarily for testing
+ _old_DEFAULT_MAX_NUM = formsets.DEFAULT_MAX_NUM
+ try:
+ formsets.DEFAULT_MAX_NUM = 3
+ # for this form, we want a limit of 4
+ ChoiceFormSet = formset_factory(Choice, max_num=4)
+ formset = ChoiceFormSet(
+ {
+ 'choices-TOTAL_FORMS': '4',
+ 'choices-INITIAL_FORMS': '0',
+ 'choices-MAX_NUM_FORMS': '4',
+ 'choices-0-choice': 'Zero',
+ 'choices-0-votes': '0',
+ 'choices-1-choice': 'One',
+ 'choices-1-votes': '1',
+ 'choices-2-choice': 'Two',
+ 'choices-2-votes': '2',
+ 'choices-3-choice': 'Three',
+ 'choices-3-votes': '3',
+ },
+ prefix='choices',
+ )
+ # This time four forms are instantiated
+ self.assertEqual(len(formset.forms), 4)
+ finally:
+ formsets.DEFAULT_MAX_NUM = _old_DEFAULT_MAX_NUM
+
data = {
'choices-TOTAL_FORMS': '1', # the number of forms rendered
View
3  tests/regressiontests/generic_inline_admin/tests.py
@@ -6,6 +6,7 @@
from django.contrib.admin.sites import AdminSite
from django.contrib.contenttypes.generic import (
generic_inlineformset_factory, GenericTabularInline)
+from django.forms.formsets import DEFAULT_MAX_NUM
from django.forms.models import ModelForm
from django.test import TestCase
from django.test.utils import override_settings
@@ -244,7 +245,7 @@ def test_get_formset_kwargs(self):
# Create a formset with default arguments
formset = media_inline.get_formset(request)
- self.assertEqual(formset.max_num, None)
+ self.assertEqual(formset.max_num, DEFAULT_MAX_NUM)
self.assertEqual(formset.can_order, False)
# Create a formset with custom keyword arguments
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