Issue #17671: Fixed a crash when use non-initialized io.BufferedRWPair.

Based on patch by Stephen Tu.

Lib/test/test_io.py

@@ -846,6 +846,16 @@ class BufferedReaderTest(unittest.TestCase, CommonBufferedTests):
         bufio.__init__(rawio)
         self.assertEqual(b"abc", bufio.read())
 
+    def test_uninitialized(self):
+        bufio = self.tp.__new__(self.tp)
+        del bufio
+        bufio = self.tp.__new__(self.tp)
+        self.assertRaisesRegex((ValueError, AttributeError),
+                               'uninitialized|has no attribute',
+                               bufio.read, 0)
+        bufio.__init__(self.MockRawIO())
+        self.assertEqual(bufio.read(0), b'')
+
     def test_read(self):
         for arg in (None, 7):
             rawio = self.MockRawIO((b"abc", b"d", b"efg"))
@@ -1096,6 +1106,16 @@ class BufferedWriterTest(unittest.TestCase, CommonBufferedTests):
         bufio.flush()
         self.assertEqual(b"".join(rawio._write_stack), b"abcghi")
 
+    def test_uninitialized(self):
+        bufio = self.tp.__new__(self.tp)
+        del bufio
+        bufio = self.tp.__new__(self.tp)
+        self.assertRaisesRegex((ValueError, AttributeError),
+                               'uninitialized|has no attribute',
+                               bufio.write, b'')
+        bufio.__init__(self.MockRawIO())
+        self.assertEqual(bufio.write(b''), 0)
+
     def test_detach_flush(self):
         raw = self.MockRawIO()
         buf = self.tp(raw)
@@ -1379,6 +1399,20 @@ class BufferedRWPairTest(unittest.TestCase):
         pair = self.tp(self.MockRawIO(), self.MockRawIO())
         self.assertFalse(pair.closed)
 
+    def test_uninitialized(self):
+        pair = self.tp.__new__(self.tp)
+        del pair
+        pair = self.tp.__new__(self.tp)
+        self.assertRaisesRegex((ValueError, AttributeError),
+                               'uninitialized|has no attribute',
+                               pair.read, 0)
+        self.assertRaisesRegex((ValueError, AttributeError),
+                               'uninitialized|has no attribute',
+                               pair.write, b'')
+        pair.__init__(self.MockRawIO(), self.MockRawIO())
+        self.assertEqual(pair.read(0), b'')
+        self.assertEqual(pair.write(b''), 0)
+
     def test_detach(self):
         pair = self.tp(self.MockRawIO(), self.MockRawIO())
         self.assertRaises(self.UnsupportedOperation, pair.detach)
@@ -1505,6 +1539,10 @@ class BufferedRandomTest(BufferedReaderTest, BufferedWriterTest):
         BufferedReaderTest.test_constructor(self)
         BufferedWriterTest.test_constructor(self)
 
+    def test_uninitialized(self):
+        BufferedReaderTest.test_uninitialized(self)
+        BufferedWriterTest.test_uninitialized(self)
+
     def test_read_and_write(self):
         raw = self.MockRawIO((b"asdf", b"ghjk"))
         rw = self.tp(raw, 8)

Misc/NEWS

@@ -20,6 +20,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #17671: Fixed a crash when use non-initialized io.BufferedRWPair.
+  Based on patch by Stephen Tu.
+
 - Issue #20594: Avoid name clash with the libc function posix_close.
 
 - Issue #19856: shutil.move() failed to move a directory to other directory

Modules/_io/bufferedio.c

@@ -2263,9 +2263,14 @@ bufferedrwpair_dealloc(rwpair *self)
 static PyObject *
 _forward_call(buffered *self, _Py_Identifier *name, PyObject *args)
 {
-    PyObject *func = _PyObject_GetAttrId((PyObject *)self, name);
-    PyObject *ret;
+    PyObject *func, *ret;
+    if (self == NULL) {
+        PyErr_SetString(PyExc_ValueError,
+                        "I/O operation on uninitialized object");
+        return NULL;
+    }
 
+    func = _PyObject_GetAttrId((PyObject *)self, name);
     if (func == NULL) {
         PyErr_SetString(PyExc_AttributeError, name->string);
         return NULL;