If a file is opened with an explicit buffer size >= 1, repeated

close() calls would attempt to free() the buffer already free()ed on
the first close().     [bug introduced with patch #788249]

Making sure that the buffer is free()ed in file object deallocation is
a belt-n-braces bit of insurance against a memory leak.

Lib/test/test_file.py

@@ -109,6 +109,23 @@ f.close()
 if not f.closed:
     raise TestFailed, 'file.closed should be true'
 
+# make sure that explicitly setting the buffer size doesn't cause
+# misbehaviour especially with repeated close() calls
+for s in (-1, 0, 1, 512):
+    try:
+        f = open(TESTFN, 'w', s)
+        f.write(str(s))
+        f.close()
+        f.close()
+        f = open(TESTFN, 'r', s)
+        d = int(f.read())
+        f.close()
+        f.close()
+    except IOError, msg:
+        raise TestFailed, 'error setting buffer size %d: %s' % (s, str(msg))
+    if d != s:
+        raise TestFailed, 'readback failure using buffer size %d'
+
 methods = ['fileno', 'flush', 'isatty', 'next', 'read', 'readinto',
            'readline', 'readlines', 'seek', 'tell', 'truncate', 'write',
            'xreadlines', '__iter__']

Misc/NEWS

@@ -194,6 +194,10 @@ Core and builtins
   the data and the data length.  Instead, the appropriate tp_as_buffer
   method is called as necessary.  
 
+- fixed: if a file is opened with an explicit buffer size >= 1, repeated 
+  close() calls would attempt to free() the buffer already free()ed on
+  the first call.
+
 
 Extension modules
 -----------------

Objects/fileobject.c

@@ -312,6 +312,7 @@ file_dealloc(PyFileObject *f)
 		(*f->f_close)(f->f_fp);
 		Py_END_ALLOW_THREADS
 	}
+	PyMem_Free(f->f_setbuf);
 	Py_XDECREF(f->f_name);
 	Py_XDECREF(f->f_mode);
 	Py_XDECREF(f->f_encoding);
@@ -358,6 +359,7 @@ file_close(PyFileObject *f)
 		f->f_fp = NULL;
 	}
 	PyMem_Free(f->f_setbuf);
+	f->f_setbuf = NULL;
 	if (sts == EOF)
 		return PyErr_SetFromErrno(PyExc_IOError);
 	if (sts != 0)