NFSv4: Fix memory corruption in nfs4_proc_open_confirm

NFSv4: Fix memory corruption in nfs4_proc_open_confirm

commit 17ead6c85c3d0ef57a14d1373f1f1cee2ce60ea8 upstream.

nfs41_wake_and_assign_slot() relies on the task->tk_msg.rpc_argp and
task->tk_msg.rpc_resp always pointing to the session sequence arguments.

nfs4_proc_open_confirm tries to pull a fast one by reusing the open
sequence structure, thus causing corruption of the NFSv4 slot table.

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>