[3.13] gh-133009: fix UAF in xml.etree.ElementTree.Element.__deepcopy__ (GH-133010) (#133806)

gh-133009: fix UAF in `xml.etree.ElementTree.Element.__deepcopy__` (GH-133010)
(cherry picked from commit 116a9f9b37)

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
This commit is contained in:
Miss Islington (bot) 2025-05-10 09:55:47 +02:00 committed by GitHub
parent 57efb77fef
commit 9718880ba9
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3 changed files with 81 additions and 7 deletions

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@ -2960,6 +2960,50 @@ class BadElementTest(ElementTestCase, unittest.TestCase):
del b
gc_collect()
def test_deepcopy_clear(self):
# Prevent crashes when __deepcopy__() clears the children list.
# See https://github.com/python/cpython/issues/133009.
class X(ET.Element):
def __deepcopy__(self, memo):
root.clear()
return self
root = ET.Element('a')
evil = X('x')
root.extend([evil, ET.Element('y')])
if is_python_implementation():
# Mutating a list over which we iterate raises an error.
self.assertRaises(RuntimeError, copy.deepcopy, root)
else:
c = copy.deepcopy(root)
# In the C implementation, we can still copy the evil element.
self.assertListEqual(list(c), [evil])
def test_deepcopy_grow(self):
# Prevent crashes when __deepcopy__() mutates the children list.
# See https://github.com/python/cpython/issues/133009.
a = ET.Element('a')
b = ET.Element('b')
c = ET.Element('c')
class X(ET.Element):
def __deepcopy__(self, memo):
root.append(a)
root.append(b)
return self
root = ET.Element('top')
evil1, evil2 = X('1'), X('2')
root.extend([evil1, c, evil2])
children = list(copy.deepcopy(root))
# mock deep copies
self.assertIs(children[0], evil1)
self.assertIs(children[2], evil2)
# true deep copies
self.assertEqual(children[1].tag, c.tag)
self.assertEqual([c.tag for c in children[3:]],
[a.tag, b.tag, a.tag, b.tag])
class MutationDeleteElementPath(str):
def __new__(cls, elem, *args):

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@ -0,0 +1,3 @@
:mod:`xml.etree.ElementTree`: Fix a crash in :meth:`Element.__deepcopy__
<object.__deepcopy__>` when the element is concurrently mutated.
Patch by Bénédikt Tran.

View file

@ -810,6 +810,8 @@ _elementtree_Element___deepcopy___impl(ElementObject *self, PyObject *memo)
PyTypeObject *tp = Py_TYPE(self);
elementtreestate *st = get_elementtree_state_by_type(tp);
// The deepcopy() helper takes care of incrementing the refcount
// of the object to copy so to avoid use-after-frees.
tag = deepcopy(st, self->tag, memo);
if (!tag)
return NULL;
@ -844,11 +846,13 @@ _elementtree_Element___deepcopy___impl(ElementObject *self, PyObject *memo)
assert(!element->extra || !element->extra->length);
if (self->extra) {
if (element_resize(element, self->extra->length) < 0)
Py_ssize_t expected_count = self->extra->length;
if (element_resize(element, expected_count) < 0) {
assert(!element->extra->length);
goto error;
}
// TODO(picnixz): check for an evil child's __deepcopy__ on 'self'
for (i = 0; i < self->extra->length; i++) {
for (i = 0; self->extra && i < self->extra->length; i++) {
PyObject* child = deepcopy(st, self->extra->children[i], memo);
if (!child || !Element_Check(st, child)) {
if (child) {
@ -858,11 +862,24 @@ _elementtree_Element___deepcopy___impl(ElementObject *self, PyObject *memo)
element->extra->length = i;
goto error;
}
if (self->extra && expected_count != self->extra->length) {
// 'self->extra' got mutated and 'element' may not have
// sufficient space to hold the next iteration's item.
expected_count = self->extra->length;
if (element_resize(element, expected_count) < 0) {
Py_DECREF(child);
element->extra->length = i;
goto error;
}
}
element->extra->children[i] = child;
}
assert(!element->extra->length);
element->extra->length = self->extra->length;
// The original 'self->extra' may be gone at this point if deepcopy()
// has side-effects. However, 'i' is the number of copied items that
// we were able to successfully copy.
element->extra->length = i;
}
/* add object to memo dictionary (so deepcopy won't visit it again) */
@ -905,13 +922,20 @@ deepcopy(elementtreestate *st, PyObject *object, PyObject *memo)
break;
}
}
if (simple)
if (simple) {
return PyDict_Copy(object);
}
/* Fall through to general case */
}
else if (Element_CheckExact(st, object)) {
return _elementtree_Element___deepcopy___impl(
// The __deepcopy__() call may call arbitrary code even if the
// object to copy is a built-in XML element (one of its children
// any of its parents in its own __deepcopy__() implementation).
Py_INCREF(object);
PyObject *res = _elementtree_Element___deepcopy___impl(
(ElementObject *)object, memo);
Py_DECREF(object);
return res;
}
}
@ -922,8 +946,11 @@ deepcopy(elementtreestate *st, PyObject *object, PyObject *memo)
return NULL;
}
Py_INCREF(object);
PyObject *args[2] = {object, memo};
return PyObject_Vectorcall(st->deepcopy_obj, args, 2, NULL);
PyObject *res = PyObject_Vectorcall(st->deepcopy_obj, args, 2, NULL);
Py_DECREF(object);
return res;
}