kernel: nfsd: fix heap overflow in NFSv4.0 LOCK replay cache

A flaw was found in the Linux kernel's NFSv4.0 server nfsd. A remote, unauthenticated attacker can exploit this heap overflow vulnerability in the NFSv4.0 LOCK replay cache. By using two cooperating NFSv4.0 clients, where one sets a lock with a large owner string and another requests a conflictin...