Issue #25498: Fix GC crash due to ctypes objects wrapping a memoryview

This was a regression caused by revision 1da9630e9b7f.  Based on patch by
Eryksun.

1 files changed, 38 insertions, 18 deletions

diff --git a/Modules/_ctypes/_ctypes.c b/Modules/_ctypes/_ctypes.c
index 2e5939c..2b27ed3 100644
--- a/Modules/_ctypes/_ctypes.c
+++ b/Modules/_ctypes/_ctypes.c
@@ -463,45 +463,65 @@ KeepRef(CDataObject *target, Py_ssize_t index, PyObject *keep);
 static PyObject *
 CDataType_from_buffer(PyObject *type, PyObject *args)
 {
-    Py_buffer buffer;
+    PyObject *obj;
+    PyObject *mv;
+    PyObject *result;
+    Py_buffer *buffer;
     Py_ssize_t offset = 0;
-    PyObject *result, *mv;
+
     StgDictObject *dict = PyType_stgdict(type);
     assert (dict);
 
-    if (!PyArg_ParseTuple(args, "w*|n:from_buffer", &buffer, &offset))
+    if (!PyArg_ParseTuple(args, "O|n:from_buffer", &obj, &offset))
         return NULL;
 
+    mv = PyMemoryView_FromObject(obj);
+    if (mv == NULL)
+        return NULL;
+
+    buffer = PyMemoryView_GET_BUFFER(mv);
+
+    if (buffer->readonly) {
+        PyErr_SetString(PyExc_TypeError,
+            "underlying buffer is not writable");
+        Py_DECREF(mv);
+        return NULL;
+    }
+
+    if (!PyBuffer_IsContiguous(buffer, 'C')) {
+        PyErr_SetString(PyExc_TypeError,
+            "underlying buffer is not C contiguous");
+        Py_DECREF(mv);
+        return NULL;
+    }
+
     if (offset < 0) {
         PyErr_SetString(PyExc_ValueError,
                         "offset cannot be negative");
-        PyBuffer_Release(&buffer);
+        Py_DECREF(mv);
         return NULL;
     }
-    if (dict->size > buffer.len - offset) {
+
+    if (dict->size > buffer->len - offset) {
         PyErr_Format(PyExc_ValueError,
-                     "Buffer size too small (%zd instead of at least %zd bytes)",
-                     buffer.len, dict->size + offset);
-        PyBuffer_Release(&buffer);
+                     "Buffer size too small "
+                     "(%zd instead of at least %zd bytes)",
+                     buffer->len, dict->size + offset);
+        Py_DECREF(mv);
         return NULL;
     }
 
-    result = PyCData_AtAddress(type, (char *)buffer.buf + offset);
+    result = PyCData_AtAddress(type, (char *)buffer->buf + offset);
     if (result == NULL) {
-        PyBuffer_Release(&buffer);
+        Py_DECREF(mv);
         return NULL;
     }
 
-    mv = PyMemoryView_FromBuffer(&buffer);
-    if (mv == NULL) {
-        PyBuffer_Release(&buffer);
+    if (-1 == KeepRef((CDataObject *)result, -1, mv)) {
+        Py_DECREF(result);
         return NULL;
     }
-    /* Hack the memoryview so that it will release the buffer. */
-    ((PyMemoryViewObject *)mv)->mbuf->master.obj = buffer.obj;
-    ((PyMemoryViewObject *)mv)->view.obj = buffer.obj;
-    if (-1 == KeepRef((CDataObject *)result, -1, mv))
-        result = NULL;
+
     return result;
 }