https://github.com/python/cpython/commit/a4ea80d52394bafffb2257abbe815c7ffdb003a3
commit: a4ea80d52394bafffb2257abbe815c7ffdb003a3
branch: main
author: Victor Stinner <vstin...@python.org>
committer: vstinner <vstin...@python.org>
date: 2025-04-22T22:09:35+02:00
summary:
gh-132713: Fix repr(list) race condition (#132801)
Hold a strong reference to the item while calling repr(item).
files:
A
Misc/NEWS.d/next/Core_and_Builtins/2025-04-22-16-38-43.gh-issue-132713.mBWTSZ.rst
M Lib/test/test_list.py
M Objects/listobject.c
diff --git a/Lib/test/test_list.py b/Lib/test/test_list.py
index ec65ed49281527..6894fba2ad1b00 100644
--- a/Lib/test/test_list.py
+++ b/Lib/test/test_list.py
@@ -118,6 +118,19 @@ def test_list_resize_overflow(self):
with self.assertRaises((MemoryError, OverflowError)):
lst *= size
+ def test_repr_mutate(self):
+ class Obj:
+ @staticmethod
+ def __repr__():
+ try:
+ mylist.pop()
+ except IndexError:
+ pass
+ return 'obj'
+
+ mylist = [Obj() for _ in range(5)]
+ self.assertEqual(repr(mylist), '[obj, obj, obj]')
+
def test_repr_large(self):
# Check the repr of large list objects
def check(n):
diff --git
a/Misc/NEWS.d/next/Core_and_Builtins/2025-04-22-16-38-43.gh-issue-132713.mBWTSZ.rst
b/Misc/NEWS.d/next/Core_and_Builtins/2025-04-22-16-38-43.gh-issue-132713.mBWTSZ.rst
new file mode 100644
index 00000000000000..877b42374a396e
--- /dev/null
+++
b/Misc/NEWS.d/next/Core_and_Builtins/2025-04-22-16-38-43.gh-issue-132713.mBWTSZ.rst
@@ -0,0 +1,2 @@
+Fix ``repr(list)`` race condition: hold a strong reference to the item while
+calling ``repr(item)``. Patch by Victor Stinner.
diff --git a/Objects/listobject.c b/Objects/listobject.c
index 12d5b33414a92a..3f665a4929f14e 100644
--- a/Objects/listobject.c
+++ b/Objects/listobject.c
@@ -583,6 +583,7 @@ list_repr_impl(PyListObject *v)
/* "[" + "1" + ", 2" * (len - 1) + "]" */
Py_ssize_t prealloc = 1 + 1 + (2 + 1) * (Py_SIZE(v) - 1) + 1;
PyUnicodeWriter *writer = PyUnicodeWriter_Create(prealloc);
+ PyObject *item = NULL;
if (writer == NULL) {
goto error;
}
@@ -594,6 +595,13 @@ list_repr_impl(PyListObject *v)
/* Do repr() on each element. Note that this may mutate the list,
so must refetch the list size on each iteration. */
for (Py_ssize_t i = 0; i < Py_SIZE(v); ++i) {
+ item = list_get_item_ref(v, i);
+ if (item == NULL) {
+ // List truncated while iterating on it
+ PyErr_Clear();
+ break;
+ }
+
if (i > 0) {
if (PyUnicodeWriter_WriteChar(writer, ',') < 0) {
goto error;
@@ -603,9 +611,10 @@ list_repr_impl(PyListObject *v)
}
}
- if (PyUnicodeWriter_WriteRepr(writer, v->ob_item[i]) < 0) {
+ if (PyUnicodeWriter_WriteRepr(writer, item) < 0) {
goto error;
}
+ Py_CLEAR(item);
}
if (PyUnicodeWriter_WriteChar(writer, ']') < 0) {
@@ -616,6 +625,7 @@ list_repr_impl(PyListObject *v)
return PyUnicodeWriter_Finish(writer);
error:
+ Py_XDECREF(item);
PyUnicodeWriter_Discard(writer);
Py_ReprLeave((PyObject *)v);
return NULL;
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