pythongh-112625: Protect bytearray from being freed by misbehaving it…

…erator inside bytearray.join (pythonGH-112626)
miss-islington · Dec 4, 2023 · 0e732d0 · 0e732d0
1 parent 23e001f
commit 0e732d0
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Showing 3 changed files with 22 additions and 1 deletion.
diff --git a/Lib/test/test_builtin.py b/Lib/test/test_builtin.py
@@ -2039,6 +2039,23 @@ def test_bytearray_extend_error(self):
         bad_iter = map(int, "X")
         self.assertRaises(ValueError, array.extend, bad_iter)
 
+    def test_bytearray_join_with_misbehaving_iterator(self):
+        # Issue #112625
+        array = bytearray(b',')
+        def iterator():
+            array.clear()
+            yield b'A'
+            yield b'B'
+        self.assertRaises(BufferError, array.join, iterator())
+
+    def test_bytearray_join_with_custom_iterator(self):
+        # Issue #112625
+        array = bytearray(b',')
+        def iterator():
+            yield b'A'
+            yield b'B'
+        self.assertEqual(bytearray(b'A,B'), array.join(iterator()))
+
     def test_construct_singletons(self):
         for const in None, Ellipsis, NotImplemented:
             tp = type(const)

diff --git a/Misc/NEWS.d/next/Core and Builtins/2023-12-03-19-34-51.gh-issue-112625.QWTlwS.rst b/Misc/NEWS.d/next/Core and Builtins/2023-12-03-19-34-51.gh-issue-112625.QWTlwS.rst
@@ -0,0 +1 @@
+Fixes a bug where a bytearray object could be cleared while iterating over an argument in the ``bytearray.join()`` method that could result in reading memory after it was freed.
diff --git a/Objects/bytearrayobject.c b/Objects/bytearrayobject.c
@@ -2007,7 +2007,10 @@ static PyObject *
 bytearray_join(PyByteArrayObject *self, PyObject *iterable_of_bytes)
 /*[clinic end generated code: output=a8516370bf68ae08 input=aba6b1f9b30fcb8e]*/
 {
-    return stringlib_bytes_join((PyObject*)self, iterable_of_bytes);
+    self->ob_exports++; // this protects `self` from being cleared/resized if `iterable_of_bytes` is a custom iterator
+    PyObject* ret = stringlib_bytes_join((PyObject*)self, iterable_of_bytes);
+    self->ob_exports--; // unexport `self`
+    return ret;
 }
 
 /*[clinic input]
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		Fixes a bug where a bytearray object could be cleared while iterating over an argument in the ``bytearray.join()`` method that could result in reading memory after it was freed.