fix(io): scope UAF patch to TextIOWrapper

vstinner · Oct 7, 2026 · Sep 12, 2026 · Sep 12, 2026 · Sep 13, 2026 · Sep 22, 2026
commit 7e1eedd3b62ca90cf93d4d8003f81f03437e25dc
diff --git a/Lib/test/test_io/test_bufferedio.py b/Lib/test/test_io/test_bufferedio.py
@@ -607,27 +607,6 @@ def test_args_error(self):
         with self.assertRaisesRegex(TypeError, "BufferedReader"):
             self.tp(self.BytesIO(), 1024, 1024, 1024)
 
-    def test_readinto_buffer_keeps_reader_alive(self):
-        # gh-157364: raw.readinto() may store the memoryview it is given, so
-        # the memoryview must keep the BufferedReader owning its memory alive.
-        stored = []
-
-        class StoringRawIO(self.MockRawIO):
-            def readinto(self, b):
-                stored.append(b)
-                return super().readinto(b)
-
-        bufio = self.tp(StoringRawIO([b"abc"]))
-        self.assertEqual(bufio.read(3), b"abc")
-        self.assertIs(stored[0].obj, bufio)
-        wr = weakref.ref(bufio)
-        del bufio
-        support.gc_collect()
-        self.assertIsNotNone(wr())
-        stored.clear()
-        support.gc_collect()
-        self.assertIsNone(wr())
-
     def test_bad_readinto_value(self):
         rawio = self.tp(self.BytesIO(b"12"))
         rawio.readinto = lambda buf: -1

diff --git a/Lib/test/test_io/test_textio.py b/Lib/test/test_io/test_textio.py
@@ -1659,6 +1659,9 @@ def readinto(self, b):
                     self.BufferedReader(raw), encoding="utf-8")
                 method = getattr(wrapper, method_name)
                 self.assertEqual(method(), "ab\n")
+                with self.assertRaisesRegex(ValueError,
+                                            "underlying buffer has been detached"):
+                    wrapper.buffer
 
     def test_reentrant_seek_during_tell(self):
         # gh-153539: reading short of _CHUNK_SIZE leaves residual bytes in the

diff --git a/Misc/NEWS.d/next/Library/2026-09-12-18-03-15.gh-issue-157364.Qd7mKs.rst b/Misc/NEWS.d/next/Library/2026-09-12-18-03-15.gh-issue-157364.Qd7mKs.rst
@@ -1,4 +1,2 @@
 Fix a use-after-free in :class:`io.TextIOWrapper` when a call to the
-underlying buffer reentrantly detaches it. The :class:`memoryview` that
-:class:`io.BufferedReader` passes to the raw stream's ``readinto()`` now keeps
-the reader alive. Patched by Shamil Abdulaev.
+underlying buffer reentrantly detaches it. Patched by Shamil Abdulaev.
diff --git a/Modules/_io/bufferedio.c b/Modules/_io/bufferedio.c
@@ -10,7 +10,6 @@
 #include "Python.h"
 #include "pycore_call.h"                // _PyObject_CallNoArgs()
 #include "pycore_fileutils.h"           // _PyFile_Flush
-#include "pycore_memoryobject.h"        // _PyMemoryView_FromBufferProc()
 #include "pycore_object.h"              // _PyObject_GC_UNTRACK()
 #include "pycore_pyerrors.h"            // _Py_FatalErrorFormat()
 #include "pycore_pylifecycle.h"         // _Py_IsInterpreterFinalizing()
@@ -255,10 +254,6 @@ typedef struct {
        isn't ready for writing. */
     Py_off_t write_end;
 
-    /* Region handed to the raw stream by _bufferedreader_raw_read(). */
-    char *raw_read_start;
-    Py_ssize_t raw_read_len;
-
     PyThread_type_lock lock;
     volatile unsigned long owner;
 
@@ -1624,25 +1619,16 @@ _io_BufferedReader___init___impl(buffered *self, PyObject *raw,
     return 0;
 }
 
-/* The memoryview passed to raw.readinto() owns a reference to the buffered
-   object so that storing it in Python code cannot outlive its memory. */
-static int
-_bufferedreader_raw_read_getbuffer(PyObject *op, Py_buffer *view, int flags)
-{
-    buffered *self = buffered_CAST(op);
-    return PyBuffer_FillInfo(view, op, self->raw_read_start,
-                             self->raw_read_len, 0, flags);
-}
-
 static Py_ssize_t
 _bufferedreader_raw_read(buffered *self, char *start, Py_ssize_t len)
 {
+    Py_buffer buf;
     PyObject *memobj, *res;
     Py_ssize_t n;
-    self->raw_read_start = start;
-    self->raw_read_len = len;
-    memobj = _PyMemoryView_FromBufferProc((PyObject *)self, PyBUF_CONTIG,
-                                          _bufferedreader_raw_read_getbuffer);
+    /* NOTE: the buffer needn't be released as its object is NULL. */
+    if (PyBuffer_FillInfo(&buf, NULL, start, len, 0, PyBUF_CONTIG) == -1)
+        return -1;
+    memobj = PyMemoryView_FromBuffer(&buf);
     if (memobj == NULL)
         return -1;
     /* NOTE: PyErr_SetFromErrno() calls PyErr_CheckSignals() when EINTR