pythongh-114685: Check flags in PyObject_GetBuffer() (pythonGH-114707)

serhiy-storchaka · web-flow · commit b7688ef71edd · 2024-01-31T13:11:35.000+02:00
PyObject_GetBuffer() now raises a SystemError if called with
PyBUF_READ or PyBUF_WRITE as flags. These flags should
only be used with the PyMemoryView_* C API.
diff --git a/Lib/test/test_buffer.py b/Lib/test/test_buffer.py
@@ -4585,6 +4585,12 @@ def test_c_buffer(self):
             buf.__release_buffer__(mv)
         self.assertEqual(buf.references, 0)
 
+    @unittest.skipIf(_testcapi is None, "requires _testcapi")
+    def test_c_buffer_invalid_flags(self):
+        buf = _testcapi.testBuf()
+        self.assertRaises(SystemError, buf.__buffer__, PyBUF_READ)
+        self.assertRaises(SystemError, buf.__buffer__, PyBUF_WRITE)
+
     def test_inheritance(self):
         class A(bytearray):
             def __buffer__(self, flags):
diff --git a/Misc/NEWS.d/next/C API/2024-01-29-12-13-24.gh-issue-114685.B07RME.rst b/Misc/NEWS.d/next/C API/2024-01-29-12-13-24.gh-issue-114685.B07RME.rst
@@ -0,0 +1,3 @@
+:c:func:`PyObject_GetBuffer` now raises a :exc:`SystemError` if called with
+:c:macro:`PyBUF_READ` or :c:macro:`PyBUF_WRITE` as flags. These flags should
+only be used with the ``PyMemoryView_*`` C API.
diff --git a/Modules/_testcapi/buffer.c b/Modules/_testcapi/buffer.c
@@ -54,8 +54,10 @@ static int
 testbuf_getbuf(testBufObject *self, Py_buffer *view, int flags)
 {
     int buf = PyObject_GetBuffer(self->obj, view, flags);
-    Py_SETREF(view->obj, Py_NewRef(self));
-    self->references++;
+    if (buf == 0) {
+        Py_SETREF(view->obj, Py_NewRef(self));
+        self->references++;
+    }
     return buf;
 }
 
diff --git a/Objects/abstract.c b/Objects/abstract.c
@@ -425,6 +425,12 @@ PyObject_AsWriteBuffer(PyObject *obj,
 int
 PyObject_GetBuffer(PyObject *obj, Py_buffer *view, int flags)
 {
+    if (flags != PyBUF_SIMPLE) {  /* fast path */
+        if (flags == PyBUF_READ || flags == PyBUF_WRITE) {
+            PyErr_BadInternalCall();
+            return -1;
+        }
+    }
     PyBufferProcs *pb = Py_TYPE(obj)->tp_as_buffer;
 
     if (pb == NULL || pb->bf_getbuffer == NULL) {

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,3 @@`
	`1`	+:c:func:`PyObject_GetBuffer` now raises a :exc:`SystemError` if called with
	`2`	+:c:macro:`PyBUF_READ` or :c:macro:`PyBUF_WRITE` as flags. These flags should
	`3`	+only be used with the ``PyMemoryView_*`` C API.
Original file line number	Diff line number	Diff line change
`@@ -54,8 +54,10 @@ static int`
`54`	`54`	`testbuf_getbuf(testBufObject self, Py_buffer view, int flags)`
`55`	`55`	`{`
`56`	`56`	`int buf = PyObject_GetBuffer(self->obj, view, flags);`
`57`		`- Py_SETREF(view->obj, Py_NewRef(self));`
`58`		`- self->references++;`
	`57`	`+ if (buf == 0) {`
	`58`	`+ Py_SETREF(view->obj, Py_NewRef(self));`
	`59`	`+ self->references++;`
	`60`	`+ }`
`59`	`61`	`return buf;`
`60`	`62`	`}`
`61`	`63`