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gh-144984: Fix crash in ExternalEntityParserCreate() error paths #144992

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gh-144984: Fix crash in ExternalEntityParserCreate() error paths #144992

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4b45e07
gh-144984: Fix crash in ExternalEntityParserCreate() error paths
raminfp Feb 19, 2026
be72e78
gh-144984: Address review: use Py_NewRef(self) for parent, add setUpC…
raminfp Feb 19, 2026
f3c1732
gh-144984: Address review: rename to cls.testcapi, add comment for as…
raminfp Feb 19, 2026
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37 changes: 37 additions & 0 deletions Lib/test/test_pyexpat.py
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Original file line number Diff line number Diff line change
Expand Up @@ -824,6 +824,43 @@ def test_parent_parser_outlives_its_subparsers__chain(self):
del subparser


class ExternalEntityParserCreateErrorTest(unittest.TestCase):
"""ExternalEntityParserCreate error paths should not crash or leak
refcounts on the parent parser.

See https://github.com/python/cpython/issues/144984.
"""

@classmethod
def setUpClass(cls):
cls.testcapi = import_helper.import_module('_testcapi')

def test_error_path_no_crash(self):
# When an allocation inside ExternalEntityParserCreate fails,
# the partially-initialized subparser is deallocated. This
# must not dereference NULL handlers or double-decrement the
# parent parser's refcount.
parser = expat.ParserCreate()
parser.buffer_text = True
rc_before = sys.getrefcount(parser)

# We avoid self.assertRaises(MemoryError) here because the
# context manager itself needs memory allocations that fail
# while the nomemory hook is active.
self.testcapi.set_nomemory(1, 10)
raised = False
try:
parser.ExternalEntityParserCreate(None)
except MemoryError:
raised = True
finally:
self.testcapi.remove_mem_hooks()
self.assertTrue(raised, "MemoryError not raised")

rc_after = sys.getrefcount(parser)
self.assertEqual(rc_after, rc_before)


class ReparseDeferralTest(unittest.TestCase):
def test_getter_setter_round_trip(self):
parser = expat.ParserCreate()
Expand Down
3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2026-02-19-12-00-00.gh-issue-144984.b93995c982.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Fix crash in :meth:`xml.parsers.expat.xmlparser.ExternalEntityParserCreate`
when an allocation fails. The error paths could dereference NULL ``handlers``
and double-decrement the parent parser's reference count.
16 changes: 7 additions & 9 deletions Modules/pyexpat.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1076,11 +1076,6 @@ pyexpat_xmlparser_ExternalEntityParserCreate_impl(xmlparseobject *self,
return NULL;
}

// The new subparser will make use of the parent XML_Parser inside of Expat.
// So we need to take subparsers into account with the reference counting
// of their parent parser.
Py_INCREF(self);

new_parser->buffer_size = self->buffer_size;
new_parser->buffer_used = 0;
new_parser->buffer = NULL;
Expand All @@ -1090,21 +1085,22 @@ pyexpat_xmlparser_ExternalEntityParserCreate_impl(xmlparseobject *self,
new_parser->ns_prefixes = self->ns_prefixes;
new_parser->itself = XML_ExternalEntityParserCreate(self->itself, context,
encoding);
new_parser->parent = (PyObject *)self;
// The new subparser will make use of the parent XML_Parser inside of Expat.
// So we need to take subparsers into account with the reference counting
// of their parent parser.
new_parser->parent = Py_NewRef(self);
new_parser->handlers = 0;
new_parser->intern = Py_XNewRef(self->intern);

if (self->buffer != NULL) {
new_parser->buffer = PyMem_Malloc(new_parser->buffer_size);
if (new_parser->buffer == NULL) {
Py_DECREF(new_parser);
Py_DECREF(self);
return PyErr_NoMemory();
}
}
if (!new_parser->itself) {
Py_DECREF(new_parser);
Py_DECREF(self);
return PyErr_NoMemory();
}

Expand All @@ -1118,7 +1114,6 @@ pyexpat_xmlparser_ExternalEntityParserCreate_impl(xmlparseobject *self,
new_parser->handlers = PyMem_New(PyObject *, i);
if (!new_parser->handlers) {
Py_DECREF(new_parser);
Py_DECREF(self);
return PyErr_NoMemory();
}
clear_handlers(new_parser, 1);
Expand Down Expand Up @@ -2489,6 +2484,9 @@ PyInit_pyexpat(void)
static void
clear_handlers(xmlparseobject *self, int initial)
{
if (self->handlers == NULL) {
return;
}
for (size_t i = 0; handler_info[i].name != NULL; i++) {
if (initial) {
self->handlers[i] = NULL;
Expand Down
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