reader: check return value of PySequence_Length

The constructor used to raise a MemoryError if files[0] returned an int, but files.__length__() did not exist.

Author: viccie30

src/systemd/_reader.c

@@ -107,6 +107,10 @@ static int strv_converter(PyObject* obj, void *_result) {
                 return 0;
 
         Py_ssize_t len = PySequence_Length(obj);
+        if (len < 0) {
+                return 0;
+        }
+
         *result = new0(char*, len + 1);
         if (!*result) {
                 set_error(-ENOMEM, NULL, NULL);
@@ -166,6 +170,10 @@ static int intlist_converter(PyObject* obj, int **_result, size_t *_len) {
                 return 0;
 
         Py_ssize_t len = PySequence_Length(obj);
+        if (len < 0) {
+                return 0;
+        }
+
         _cleanup_free_ int *result = new0(int, len);
 
         if (!result) {

src/systemd/test/test_reader.py

@@ -4,5 +4,15 @@
 
 import pytest
 
+class SequenceWithoutLength:
+    def __getitem__(self, index: int) -> int:
+        return 5
+
+    # no __length__ implementation
+
 def test_reader_init_with_empty_files_sequence():
     _Reader(files=[], flags=0)
+
+def test_reader_init_with_sequence_without_length():
+    with pytest.raises(TypeError):
+        _Reader(files=SequenceWithoutLength(), flags=0)