The clone_mnt function in fs/namespace.c in the Linux kernel before 3.8.6 does not properly restrict changes to the MNT_READONLY flag, which allows local users to bypass an intended read-only property of a filesystem by leveraging a separate mount namespace.
https://github.com/torvalds/linux/commit/132c94e31b8bca8ea921f9f96a57d684fa4ae0a9
http://www.openwall.com/lists/oss-security/2013/04/16/11