fs/nfs/nfs4client.c in the Linux kernel before 5.13.4 has incorrect
connection-setup ordering, which allows operators of remote NFSv4 servers
to cause a denial of service (hanging of mounts) by arranging for those
servers to be unreachable during trunking detection.

Michael Wakabayashi discovered that the NFSv4 client implementation in the
Linux kernel did not properly order connection setup operations. An
attacker controlling a remote NFS server could use this to cause a denial
of service on the client.