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[3.13] gh-152682: Fix NULL dereference on OOM in symtable_visit_type_param_bound_or_default (GH-152684) #152697

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Merged
JelleZijlstra merged 2 commits into from
Jul 6, 2026
Merged

[3.13] gh-152682: Fix NULL dereference on OOM in symtable_visit_type_param_bound_or_default (GH-152684) #152697

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ef59f2d
gh-152682: Fix NULL dereference on OOM in `symtable_visit_type_param_…
petrvaganoff Jun 30, 2026
f105025
Remove test
StanFromIreland Jul 1, 2026
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gh-152682: Fix NULL dereference on OOM in `symtable_visit_type_param_… 
…bound_or_default` (GH-152684)

In `symtable_visit_type_param_bound_or_default()`, when a reserved name
(e.g. `__classdict__`) is used as a type parameter, `PyUnicode_FromFormat()`
is called to build the SyntaxError message. If the allocation fails and
returns NULL, the subsequent `PyErr_SetObject()` and `Py_DECREF()` calls
would dereference NULL, causing a segfault.

Fix by returning 0 immediately when `PyUnicode_FromFormat()` returns NULL.
This propagates the MemoryError set by `PyUnicode_FromFormat()`.

The bug was introduced in gh-128632 (commit 891c61c).
(cherry picked from commit 10ed03e)

Co-authored-by: Petr Vaganov <petrvaganoff@gmail.com>
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@petrvaganoff @miss-islington
petrvaganoff authored and miss-islington committed Jun 30, 2026
commit ef59f2dbc1ec7a7c9f72eec6c2ed8071b4648011
17 changes: 17 additions & 0 deletions Lib/test/test_syntax.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2244,6 +2244,7 @@ def f(x: *b)
import unittest

from test import support
from test.support.script_helper import assert_python_ok

class SyntaxTestCase(unittest.TestCase):

Expand Down Expand Up @@ -2496,6 +2497,22 @@ class A:
class B[{name}]: pass
""", "<testcase>", mode="exec")

@support.nomemtest
def test_disallowed_type_param_names_oom(self):
# gh-152682: Don't crash on OOM when formatting the SyntaxError message
# in symtable_visit_type_param_bound_or_default.
code = textwrap.dedent("""\
import _testcapi
_testcapi.set_nomemory(0)
try:
compile("class A[__classdict__]: pass", "<string>", "exec")
except MemoryError:
pass
else:
raise RuntimeError('MemoryError not raised')
""")
assert_python_ok("-c", code)

@support.cpython_only
def test_nested_named_except_blocks(self):
code = ""
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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2026-06-30-14-00-00.gh-issue-152682.yId7e5.rst
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@@ -0,0 +1,3 @@
Fix NULL pointer dereference in :func:`compile` when a reserved name (e.g.
``__classdict__``) is used as a type parameter name and memory allocation
fails while formatting the error message.
3 changes: 3 additions & 0 deletions Python/symtable.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2318,6 +2318,9 @@ symtable_visit_type_param_bound_or_default(

PyObject *error_msg = PyUnicode_FromFormat("reserved name '%U' cannot be "
"used for type parameter", name);
if (error_msg == NULL) {
return 0;
}
PyErr_SetObject(PyExc_SyntaxError, error_msg);
Py_DECREF(error_msg);
PyErr_RangedSyntaxLocationObject(st->st_filename,
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