bpo-25455: Fixed crashes in repr of recursive buffered file-like objects. (#514)

Lib/test/test_fileio.py

@@ -10,7 +10,7 @@ from weakref import proxy
 from functools import wraps
 
 from test.support import (TESTFN, TESTFN_UNICODE, check_warnings, run_unittest,
-                          make_bad_fd, cpython_only)
+                          make_bad_fd, cpython_only, swap_attr)
 from collections import UserList
 
 import _io  # C implementation of io
@@ -176,6 +176,12 @@ class AutoFileTests:
         finally:
             os.close(fd)
 
+    def testRecursiveRepr(self):
+        # Issue #25455
+        with swap_attr(self.f, 'name', self.f):
+            with self.assertRaises(RuntimeError):
+                repr(self.f)  # Should not crash
+
     def testErrors(self):
         f = self.f
         self.assertFalse(f.isatty())

Lib/test/test_io.py

@@ -1014,6 +1014,16 @@ class CommonBufferedTests:
         raw.name = b"dummy"
         self.assertEqual(repr(b), "<%s name=b'dummy'>" % clsname)
 
+    def test_recursive_repr(self):
+        # Issue #25455
+        raw = self.MockRawIO()
+        b = self.tp(raw)
+        with support.swap_attr(raw, 'name', b):
+            try:
+                repr(b)  # Should not crash
+            except RuntimeError:
+                pass
+
     def test_flush_error_on_close(self):
         # Test that buffered file is closed despite failed flush
         # and that flush() is called before file closed.
@@ -2435,6 +2445,16 @@ class TextIOWrapperTest(unittest.TestCase):
         t.buffer.detach()
         repr(t)  # Should not raise an exception
 
+    def test_recursive_repr(self):
+        # Issue #25455
+        raw = self.BytesIO()
+        t = self.TextIOWrapper(raw)
+        with support.swap_attr(raw, 'name', t):
+            try:
+                repr(t)  # Should not crash
+            except RuntimeError:
+                pass
+
     def test_line_buffering(self):
         r = self.BytesIO()
         b = self.BufferedWriter(r, 1000)

Misc/NEWS

@@ -281,6 +281,8 @@ Extension Modules
 Library
 -------
 
+- bpo-25455: Fixed crashes in repr of recursive buffered file-like objects.
+
 - bpo-29800: Fix crashes in partial.__repr__ if the keys of partial.keywords
   are not strings.  Patch by Michael Seifert.
 

Modules/_io/bufferedio.c

@@ -1415,8 +1415,18 @@ buffered_repr(buffered *self)
         res = PyUnicode_FromFormat("<%s>", Py_TYPE(self)->tp_name);
     }
     else {
+        int status = Py_ReprEnter((PyObject *)self);
+        res = NULL;
+        if (status == 0) {
             res = PyUnicode_FromFormat("<%s name=%R>",
                                        Py_TYPE(self)->tp_name, nameobj);
+            Py_ReprLeave((PyObject *)self);
+        }
+        else if (status > 0) {
+            PyErr_Format(PyExc_RuntimeError,
+                         "reentrant call inside %s.__repr__",
+                         Py_TYPE(self)->tp_name);
+        }
         Py_DECREF(nameobj);
     }
     return res;

Modules/_io/fileio.c

@@ -1082,9 +1082,19 @@ fileio_repr(fileio *self)
             self->fd, mode_string(self), self->closefd ? "True" : "False");
     }
     else {
+        int status = Py_ReprEnter((PyObject *)self);
+        res = NULL;
+        if (status == 0) {
             res = PyUnicode_FromFormat(
                 "<_io.FileIO name=%R mode='%s' closefd=%s>",
                 nameobj, mode_string(self), self->closefd ? "True" : "False");
+            Py_ReprLeave((PyObject *)self);
+        }
+        else if (status > 0) {
+            PyErr_Format(PyExc_RuntimeError,
+                         "reentrant call inside %s.__repr__",
+                         Py_TYPE(self)->tp_name);
+        }
         Py_DECREF(nameobj);
     }
     return res;

Modules/_io/textio.c

@@ -2483,6 +2483,7 @@ static PyObject *
 textiowrapper_repr(textio *self)
 {
     PyObject *nameobj, *modeobj, *res, *s;
+    int status;
 
     CHECK_INITIALIZED(self);
 
@@ -2490,6 +2491,15 @@ textiowrapper_repr(textio *self)
     if (res == NULL)
         return NULL;
 
+    status = Py_ReprEnter((PyObject *)self);
+    if (status != 0) {
+        if (status > 0) {
+            PyErr_Format(PyExc_RuntimeError,
+                         "reentrant call inside %s.__repr__",
+                         Py_TYPE(self)->tp_name);
+        }
+        goto error;
+    }
     nameobj = _PyObject_GetAttrId((PyObject *) self, &PyId_name);
     if (nameobj == NULL) {
         if (PyErr_ExceptionMatches(PyExc_Exception))
@@ -2504,7 +2514,7 @@ textiowrapper_repr(textio *self)
             goto error;
         PyUnicode_AppendAndDel(&res, s);
         if (res == NULL)
-            return NULL;
+            goto error;
     }
     modeobj = _PyObject_GetAttrId((PyObject *) self, &PyId_mode);
     if (modeobj == NULL) {
@@ -2520,14 +2530,21 @@ textiowrapper_repr(textio *self)
             goto error;
         PyUnicode_AppendAndDel(&res, s);
         if (res == NULL)
-            return NULL;
+            goto error;
     }
     s = PyUnicode_FromFormat("%U encoding=%R>",
                              res, self->encoding);
     Py_DECREF(res);
+    if (status == 0) {
+        Py_ReprLeave((PyObject *)self);
+    }
     return s;
-error:
+
+  error:
     Py_XDECREF(res);
+    if (status == 0) {
+        Py_ReprLeave((PyObject *)self);
+    }
     return NULL;
 }