gh-109521: Fix obscure cases handling in PyImport_GetImporter() (GH-109522)

PyImport_GetImporter() now sets RuntimeError if it fails to get sys.path_hooks
or sys.path_importer_cache or they are not list and dict correspondingly.

Previously it could return NULL without setting error in obscure cases,
crash or raise SystemError if these attributes have wrong type.

1 files changed, 21 insertions, 5 deletions

diff --git a/Python/import.c b/Python/import.c
index 9b0be02..5a06cb3 100644
--- a/Python/import.c
+++ b/Python/import.c
@@ -2363,9 +2363,14 @@ get_path_importer(PyThreadState *tstate, PyObject *path_importer_cache,
     PyObject *importer;
     Py_ssize_t j, nhooks;
 
-    /* These conditions are the caller's responsibility: */
-    assert(PyList_Check(path_hooks));
-    assert(PyDict_Check(path_importer_cache));
+    if (!PyList_Check(path_hooks)) {
+        PyErr_SetString(PyExc_RuntimeError, "sys.path_hooks is not a list");
+        return NULL;
+    }
+    if (!PyDict_Check(path_importer_cache)) {
+        PyErr_SetString(PyExc_RuntimeError, "sys.path_importer_cache is not a dict");
+        return NULL;
+    }
 
     nhooks = PyList_Size(path_hooks);
     if (nhooks < 0)
@@ -2408,11 +2413,22 @@ PyImport_GetImporter(PyObject *path)
 {
     PyThreadState *tstate = _PyThreadState_GET();
     PyObject *path_importer_cache = PySys_GetObject("path_importer_cache");
+    if (path_importer_cache == NULL) {
+        PyErr_SetString(PyExc_RuntimeError, "lost sys.path_importer_cache");
+        return NULL;
+    }
+    Py_INCREF(path_importer_cache);
     PyObject *path_hooks = PySys_GetObject("path_hooks");
-    if (path_importer_cache == NULL || path_hooks == NULL) {
+    if (path_hooks == NULL) {
+        PyErr_SetString(PyExc_RuntimeError, "lost sys.path_hooks");
+        Py_DECREF(path_importer_cache);
         return NULL;
     }
-    return get_path_importer(tstate, path_importer_cache, path_hooks, path);
+    Py_INCREF(path_hooks);
+    PyObject *importer = get_path_importer(tstate, path_importer_cache, path_hooks, path);
+    Py_DECREF(path_hooks);
+    Py_DECREF(path_importer_cache);
+    return importer;
 }