Skip to content

gh-146056: Fix TreeBuilder stack in xml.etree #146062

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Closed
vstinner wants to merge 1 commit into from
+21 −3
Closed

gh-146056: Fix TreeBuilder stack in xml.etree #146062

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
18 changes: 18 additions & 0 deletions Lib/test/test_xml_etree_c.py
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -1,4 +1,5 @@
# xml.etree test for cElementTree
import gc
import io
import struct
from test import support
Expand Down Expand Up @@ -203,6 +204,23 @@ def test_disallow_instantiation(self):
iter_type = type(root.iter())
support.check_disallow_instantiation(self, iter_type)

def test_tree_builder_stack(self):
builder = cET.TreeBuilder()
for x in range(10):
builder.start("a", {})
for x in range(10):
builder.end("a")
root = builder.close()

# Find the internal TreeBuilder stack list using gc.get_referrers()
for ref in gc.get_referrers(root[0]):
if isinstance(ref, list):
# Check that the list doesn't contain NULL items (gh-146056)
repr(ref)
break
else:
self.fail("failed to find TreeBuilder stack list")


@unittest.skipUnless(cET, 'requires _elementtree')
class TestAliasWorking(unittest.TestCase):
Expand Down
6 changes: 3 additions & 3 deletions Modules/_elementtree.c
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -2431,7 +2431,7 @@ treebuilder_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
t->element_factory = NULL;
t->comment_factory = NULL;
t->pi_factory = NULL;
t->stack = PyList_New(20);
t->stack = PyList_New(0);
Copy link
Member

@serhiy-storchaka serhiy-storchaka Mar 18, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

This can have performance impact.

if (!t->stack) {
Py_DECREF(t->this);
Py_DECREF(t->last);
Expand Down Expand Up @@ -2856,9 +2856,9 @@ treebuilder_handle_end(TreeBuilderObject* self, PyObject* tag)

item = self->last;
self->last = Py_NewRef(self->this);
Py_XSETREF(self->last_for_tail, self->last);
Py_XSETREF(self->last_for_tail, Py_NewRef(self->last));
Copy link
Member

@serhiy-storchaka serhiy-storchaka Mar 18, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

This is unrelated.

If rewrite this code to be more explicit or safe, I would write something like

    PyObject *last = self->last;
    PyObject *last_for_tail = self->last_for_tail;
    PyObject *this = self->this;
    self->index--;
    self->this = Py_NewRef(PyList_GET_ITEM(self->stack, self->index));
    self->last = Py_NewRef(this);
    self->last_for_tail = Py_NewRef(this);
    Py_DECREF(last);
    Py_XDECREF(last_for_tail);

    if (treebuilder_append_event(self, self->end_event_obj, this) < 0) {
        Py_DECREF(this);
        return NULL;
    }

    return this;

But we should also look a the other ends -- how these attributes are set in other code in this file. This is a separate issue.

Copy link
Member Author

@vstinner vstinner Mar 19, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

I wrote #146167 which uses your suggestion.

self->index--;
self->this = Py_NewRef(PyList_GET_ITEM(self->stack, self->index));
Py_SETREF(self->this, Py_NewRef(PyList_GET_ITEM(self->stack, self->index)));
Py_DECREF(item);

if (treebuilder_append_event(self, self->end_event_obj, self->last) < 0)
Expand Down
Loading