https://github.com/python/cpython/commit/53be7d47b7712e642e6992a2896682884632b15e
commit: 53be7d47b7712e642e6992a2896682884632b15e
branch: main
author: T. Wouters <[email protected]>
committer: encukou <[email protected]>
date: 2026-10-09T13:59:27+02:00
summary:
gh-158918: Reduce C stack usage of `_PyModule_IsPossiblyShadowing`. (GH-158919)
Reduce C stack usage of `_PyModule_IsPossiblyShadowing`, which could
potentially cause stack overflows during module attribute access while
deeply recursing in agressively optimized builds.
files:
A
Misc/NEWS.d/next/Core_and_Builtins/2026-10-06-14-12-49.gh-issue-158918.TDVkZx.rst
M Objects/moduleobject.c
diff --git
a/Misc/NEWS.d/next/Core_and_Builtins/2026-10-06-14-12-49.gh-issue-158918.TDVkZx.rst
b/Misc/NEWS.d/next/Core_and_Builtins/2026-10-06-14-12-49.gh-issue-158918.TDVkZx.rst
new file mode 100644
index 000000000000000..8355186be58858a
--- /dev/null
+++
b/Misc/NEWS.d/next/Core_and_Builtins/2026-10-06-14-12-49.gh-issue-158918.TDVkZx.rst
@@ -0,0 +1,3 @@
+Reduce C stack usage of ``_PyModule_IsPossiblyShadowing``, which could
+potentially cause stack overflows during module attribute access while
+deeply recursing in agressively optimized builds.
diff --git a/Objects/moduleobject.c b/Objects/moduleobject.c
index 164f24e69c69bae..7a5d14c538391dc 100644
--- a/Objects/moduleobject.c
+++ b/Objects/moduleobject.c
@@ -1238,6 +1238,10 @@ _PyModuleSpec_GetFileOrigin(PyObject *spec, PyObject
**p_origin)
int
_PyModule_IsPossiblyShadowing(PyObject *origin)
{
+ int result = 0;
+ wchar_t *root = NULL;
+ wchar_t *sys_path_0_buf = NULL;
+
// origin must be a unicode subtype
// Returns 1 if the module at origin could be shadowing a module of the
// same name later in the module search path. The condition we check is
basically:
@@ -1256,24 +1260,21 @@ _PyModule_IsPossiblyShadowing(PyObject *origin)
}
// root = os.path.dirname(origin.removesuffix(os.sep + "__init__.py"))
- wchar_t root[MAXPATHLEN + 1];
- Py_ssize_t size = PyUnicode_AsWideChar(origin, root, MAXPATHLEN);
- if (size < 0) {
+ root = PyUnicode_AsWideCharString(origin, NULL);
+ if (root == NULL) {
return -1;
}
- assert(size <= MAXPATHLEN);
- root[size] = L'\0';
wchar_t *sep = wcsrchr(root, SEP);
if (sep == NULL) {
- return 0;
+ goto done;
}
// If it's a package then we need to look one directory further up
if (wcscmp(sep + 1, L"__init__.py") == 0) {
*sep = L'\0';
sep = wcsrchr(root, SEP);
if (sep == NULL) {
- return 0;
+ goto done;
}
}
*sep = L'\0';
@@ -1281,21 +1282,30 @@ _PyModule_IsPossiblyShadowing(PyObject *origin)
// sys.path[0] or os.getcwd()
wchar_t *sys_path_0 = config->sys_path_0;
if (!sys_path_0) {
- return 0;
+ goto done;
}
- wchar_t sys_path_0_buf[MAXPATHLEN];
if (sys_path_0[0] == L'\0') {
// if sys.path[0] == "", treat it as if it were the current directory
+ sys_path_0_buf = PyMem_Malloc(MAXPATHLEN * sizeof(wchar_t));
+ if (sys_path_0_buf == NULL) {
+ PyErr_NoMemory();
+ result = -1;
+ goto done;
+ }
if (!_Py_wgetcwd(sys_path_0_buf, MAXPATHLEN)) {
// If we failed to getcwd, don't raise an exception and instead
// let the caller proceed assuming no shadowing
- return 0;
+ goto done;
}
sys_path_0 = sys_path_0_buf;
}
- int result = wcscmp(sys_path_0, root) == 0;
+ result = (wcscmp(sys_path_0, root) == 0);
+
+done:
+ PyMem_Free(root);
+ PyMem_Free(sys_path_0_buf);
return result;
}
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