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gh-148735: Fix a UAF in `Element.findtext()` by StanFromIreland · Pull Request #148738 · python/cpython · GitHub

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10 changes: 10 additions & 0 deletions Lib/test/test_xml_etree.py
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Original file line number Diff line number Diff line change
Expand Up @@ -3258,6 +3258,16 @@ def test_findtext_with_mutating(self):
e.extend([ET.Element('bar')])
e.findtext(cls(e, 'x'))

def test_findtext_with_mutating_non_none_text(self):
for cls in [MutationDeleteElementPath, MutationClearElementPath]:
with self.subTest(cls):
e = ET.Element('foo')
child = ET.Element('bar')
child.text = str(object())
e.append(child)
del child
repr(e.findtext(cls(e, 'x')))

def test_findtext_with_error(self):
e = ET.Element('foo')
e.extend([ET.Element('bar')])
Expand Down
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters. Learn more about bidirectional Unicode characters
Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
:mod:`xml.etree.ElementTree`: Fix a use-after-free in
:meth:`Element.findtext <xml.etree.ElementTree.Element.findtext>` when the
element tree is mutated concurrently during the search.
22 changes: 9 additions & 13 deletions Modules/_elementtree.c
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Original file line number Diff line number Diff line change
Expand Up @@ -572,7 +572,7 @@ element_get_attrib(ElementObject* self)
LOCAL(PyObject*)
element_get_text(ElementObject* self)
{
/* return borrowed reference to text attribute */
/* return new reference to text attribute */

PyObject *res = self->text;

Expand All @@ -587,13 +587,13 @@ element_get_text(ElementObject* self)
}
}

return res;
return Py_NewRef(res);
}

LOCAL(PyObject*)
element_get_tail(ElementObject* self)
{
/* return borrowed reference to text attribute */
/* return new reference to tail attribute */

PyObject *res = self->tail;

Expand All @@ -608,7 +608,7 @@ element_get_tail(ElementObject* self)
}
}

return res;
return Py_NewRef(res);
}

static PyObject*
Expand Down Expand Up @@ -1350,9 +1350,9 @@ _elementtree_Element_findtext_impl(ElementObject *self, PyTypeObject *cls,
PyObject *text = element_get_text((ElementObject *)item);
Py_DECREF(item);
if (text == Py_None) {
Py_DECREF(text);
return Py_GetConstant(Py_CONSTANT_EMPTY_STR);
}
Py_XINCREF(text);
return text;
}
Py_DECREF(item);
Expand Down Expand Up @@ -2055,16 +2055,14 @@ static PyObject*
element_text_getter(PyObject *op, void *closure)
{
ElementObject *self = _Element_CAST(op);
PyObject *res = element_get_text(self);
return Py_XNewRef(res);
return element_get_text(self);
}

static PyObject*
element_tail_getter(PyObject *op, void *closure)
{
ElementObject *self = _Element_CAST(op);
PyObject *res = element_get_tail(self);
return Py_XNewRef(res);
return element_get_tail(self);
}

static PyObject*
Expand Down Expand Up @@ -2307,16 +2305,14 @@ elementiter_next(PyObject *op)
continue;

gettext:
Py_DECREF(elem);
if (!text) {
Py_DECREF(elem);
return NULL;
}
if (text == Py_None) {
Py_DECREF(elem);
Py_DECREF(text);
}
else {
Py_INCREF(text);
Py_DECREF(elem);
rc = PyObject_IsTrue(text);
if (rc > 0)
return text;
Expand Down
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