Fixed #20347 -- Allowed customizing the maximum number of instantiated forms in formsets.

Co-authored-by: ethurgood <ethurgood@gmail.com>

4 files changed, 58 insertions, 11 deletions

diff --git a/docs/ref/forms/formsets.txt b/docs/ref/forms/formsets.txt
index 778ae20db3..e145eeb103 100644
--- a/docs/ref/forms/formsets.txt
+++ b/docs/ref/forms/formsets.txt
@@ -11,8 +11,12 @@ Formset API reference. For introductory material about formsets, see the
 ``formset_factory``
 ===================
 
-.. function:: formset_factory(form, formset=BaseFormSet, extra=1, can_order=False, can_delete=False, max_num=None, validate_max=False, min_num=None, validate_min=False)
+.. function:: formset_factory(form, formset=BaseFormSet, extra=1, can_order=False, can_delete=False, max_num=None, validate_max=False, min_num=None, validate_min=False, absolute_max=None)
 
     Returns a ``FormSet`` class for the given ``form`` class.
 
     See :doc:`formsets </topics/forms/formsets>` for example usage.
+
+    .. versionchanged:: 3.2
+
+        The ``absolute_max`` argument was added.
diff --git a/docs/ref/forms/models.txt b/docs/ref/forms/models.txt
index c5ddf99011..e18660b3c2 100644
--- a/docs/ref/forms/models.txt
+++ b/docs/ref/forms/models.txt
@@ -52,7 +52,7 @@ Model Form API reference. For introductory material about model forms, see the
 ``modelformset_factory``
 ========================
 
-.. function:: modelformset_factory(model, form=ModelForm, formfield_callback=None, formset=BaseModelFormSet, extra=1, can_delete=False, can_order=False, max_num=None, fields=None, exclude=None, widgets=None, validate_max=False, localized_fields=None, labels=None, help_texts=None, error_messages=None, min_num=None, validate_min=False, field_classes=None)
+.. function:: modelformset_factory(model, form=ModelForm, formfield_callback=None, formset=BaseModelFormSet, extra=1, can_delete=False, can_order=False, max_num=None, fields=None, exclude=None, widgets=None, validate_max=False, localized_fields=None, labels=None, help_texts=None, error_messages=None, min_num=None, validate_min=False, field_classes=None, absolute_max=None)
 
     Returns a ``FormSet`` class for the given ``model`` class.
 
@@ -62,16 +62,20 @@ Model Form API reference. For introductory material about model forms, see the
     through to :func:`~django.forms.models.modelform_factory`.
 
     Arguments ``formset``, ``extra``, ``max_num``, ``can_order``,
-    ``can_delete`` and ``validate_max`` are passed through to
-    :func:`~django.forms.formsets.formset_factory`. See :doc:`formsets
+    ``can_delete``, ``validate_max``, and ``absolute_max`` are passed through
+    to :func:`~django.forms.formsets.formset_factory`. See :doc:`formsets
     </topics/forms/formsets>` for details.
 
     See :ref:`model-formsets` for example usage.
 
+    .. versionchanged:: 3.2
+
+        The ``absolute_max`` argument was added.
+
 ``inlineformset_factory``
 =========================
 
-.. function:: inlineformset_factory(parent_model, model, form=ModelForm, formset=BaseInlineFormSet, fk_name=None, fields=None, exclude=None, extra=3, can_order=False, can_delete=True, max_num=None, formfield_callback=None, widgets=None, validate_max=False, localized_fields=None, labels=None, help_texts=None, error_messages=None, min_num=None, validate_min=False, field_classes=None)
+.. function:: inlineformset_factory(parent_model, model, form=ModelForm, formset=BaseInlineFormSet, fk_name=None, fields=None, exclude=None, extra=3, can_order=False, can_delete=True, max_num=None, formfield_callback=None, widgets=None, validate_max=False, localized_fields=None, labels=None, help_texts=None, error_messages=None, min_num=None, validate_min=False, field_classes=None, absolute_max=None)
 
     Returns an ``InlineFormSet`` using :func:`modelformset_factory` with
     defaults of ``formset=``:class:`~django.forms.models.BaseInlineFormSet`,
@@ -81,3 +85,7 @@ Model Form API reference. For introductory material about model forms, see the
     the ``parent_model``, you must specify a ``fk_name``.
 
     See :ref:`inline-formsets` for example usage.
+
+    .. versionchanged:: 3.2
+
+        The ``absolute_max`` argument was added.
diff --git a/docs/releases/3.2.txt b/docs/releases/3.2.txt
index 2ff09c69b0..03f485b224 100644
--- a/docs/releases/3.2.txt
+++ b/docs/releases/3.2.txt
@@ -136,7 +136,10 @@ File Uploads
 Forms
 ~~~~~
 
-* ...
+* The new ``absolute_max`` argument for :func:`.formset_factory`,
+  :func:`.inlineformset_factory`, and :func:`.modelformset_factory` allows
+  customizing the maximum number of forms that can be instantiated when
+  supplying ``POST`` data. See :ref:`formsets-absolute-max` for more details.
 
 Generic Views
 ~~~~~~~~~~~~~
diff --git a/docs/topics/forms/formsets.txt b/docs/topics/forms/formsets.txt
index 3b5775cabb..b3e696ed8c 100644
--- a/docs/topics/forms/formsets.txt
+++ b/docs/topics/forms/formsets.txt
@@ -126,6 +126,38 @@ affect validation.  If ``validate_max=True`` is passed to the
 :func:`~django.forms.formsets.formset_factory`, then ``max_num`` will affect
 validation.  See :ref:`validate_max`.
 
+.. _formsets-absolute-max:
+
+Limiting the maximum number of instantiated forms
+=================================================
+
+.. versionadded:: 3.2
+
+The ``absolute_max`` parameter to :func:`.formset_factory` allows limiting the
+number of forms that can be instantiated when supplying ``POST`` data. This
+protects against memory exhaustion attacks using forged ``POST`` requests::
+
+    >>> from django.forms.formsets import formset_factory
+    >>> from myapp.forms import ArticleForm
+    >>> ArticleFormSet = formset_factory(ArticleForm, absolute_max=1500)
+    >>> data = {
+    ...     'form-TOTAL_FORMS': '1501',
+    ...     'form-INITIAL_FORMS': '0',
+    ...     'form-MAX_NUM_FORMS': '',
+    ... }
+    >>> formset = ArticleFormSet(data)
+    >>> len(formset.forms)
+    1500
+    >>> formset.is_valid()
+    False
+    >>> formset.non_form_errors()
+    ['Please submit 1000 or fewer forms.']
+
+When ``absolute_max`` is None, it defaults to ``max_num + 1000``. (If
+``max_num`` is ``None``, it defaults to ``2000``).
+
+If ``absolute_max`` is less than ``max_num``, a ``ValueError`` will be raised.
+
 Formset validation
 ==================
 
@@ -348,11 +380,11 @@ excessive.
 .. note::
 
     Regardless of ``validate_max``, if the number of forms in a data set
-    exceeds ``max_num`` by more than 1000, then the form will fail to validate
-    as if ``validate_max`` were set, and additionally only the first 1000
-    forms above ``max_num`` will be validated.  The remainder will be
-    truncated entirely.  This is to protect against memory exhaustion attacks
-    using forged POST requests.
+    exceeds ``absolute_max``, then the form will fail to validate as if
+    ``validate_max`` were set, and additionally only the first ``absolute_max``
+    forms will be validated. The remainder will be truncated entirely. This is
+    to protect against memory exhaustion attacks using forged POST requests.
+    See :ref:`formsets-absolute-max`.
 
 ``validate_min``
 ----------------