# HG changeset patch
# Parent bc1a178b3bc8b63feebb3f7021813247e4c7f513

diff -r bc1a178b3bc8 Lib/test/test_bytes.py
--- a/Lib/test/test_bytes.py	Sat Apr 18 05:54:02 2015 +0200
+++ b/Lib/test/test_bytes.py	Tue May 19 14:12:13 2015 +0000
@@ -985,6 +985,22 @@
         b.extend(range(100, 110))
         self.assertEqual(list(b), list(range(10, 110)))
 
+    def test_fifo_overrun(self):
+        # Test for issue #23985, a buffer overrun when implementing a FIFO
+        # Build Python with "./configure --with-pydebug" for best results
+        b = bytearray(10)
+        b.pop()  # Defeat expanding buffer off-by-one quirk
+        del b[:1]  # Advance start pointer without reallocating
+        b += bytes(2)  # Append exactly the number of deleted bytes
+        del b  # Free memory buffer, allowing pydebug verification
+
+    def test_del_expand(self):
+        # Reducing the size should not expand the buffer (issue #23985)
+        b = bytearray(10)
+        size = sys.getsizeof(b)
+        del b[:1]
+        self.assertLessEqual(sys.getsizeof(b), size)
+
     def test_extended_set_del_slice(self):
         indices = (0, None, 1, 3, 19, 300, 1<<333, -1, -2, -31, -300)
         for start in indices:
diff -r bc1a178b3bc8 Objects/bytearrayobject.c
--- a/Objects/bytearrayobject.c	Sat Apr 18 05:54:02 2015 +0200
+++ b/Objects/bytearrayobject.c	Tue May 19 14:12:13 2015 +0000
@@ -186,7 +186,7 @@
         return -1;
     }
 
-    if (size + logical_offset + 1 < alloc) {
+    if (size + logical_offset + 1 <= alloc) {
         /* Current buffer is large enough to host the requested size,
            decide on a strategy. */
         if (size < alloc / 2) {
@@ -330,11 +330,7 @@
         PyBuffer_Release(&vo);
         return PyErr_NoMemory();
     }
-    if (size < self->ob_alloc) {
-        Py_SIZE(self) = size;
-        PyByteArray_AS_STRING(self)[Py_SIZE(self)] = '\0'; /* Trailing null byte */
-    }
-    else if (PyByteArray_Resize((PyObject *)self, size) < 0) {
+    if (PyByteArray_Resize((PyObject *)self, size) < 0) {
         PyBuffer_Release(&vo);
         return NULL;
     }