check the result of PyByteArray_Resize in readline() (closes #27211)

Misc/NEWS

@@ -89,6 +89,8 @@ Core and Builtins
 Library
 -------
 
+- Issue #27211: Fix possible memory corruption in io.IOBase.readline().
+
 - Issue #27114: Fix SSLContext._load_windows_store_certs fails with
   PermissionError
 

Modules/_io/iobase.c

@@ -529,7 +529,10 @@ iobase_readline(PyObject *self, PyObject *args)
         }
 
         old_size = PyByteArray_GET_SIZE(buffer);
-        PyByteArray_Resize(buffer, old_size + PyBytes_GET_SIZE(b));
+        if (PyByteArray_Resize(buffer, old_size + PyBytes_GET_SIZE(b)) < 0) {
+            Py_DECREF(b);
+            goto fail;
+        }
         memcpy(PyByteArray_AS_STRING(buffer) + old_size,
                PyBytes_AS_STRING(b), PyBytes_GET_SIZE(b));