ocfs2: check if cluster name exists before deref

ocfs2: check if cluster name exists before deref

Commit c74a3bdd9b52 ("ocfs2: add clustername to cluster connection") is
trying to strlcpy a string which was explicitly passed as NULL in the
very same patch, triggering a NULL ptr deref.

  BUG: unable to handle kernel NULL pointer dereference at           (null)
  IP: strlcpy (lib/string.c:388 lib/string.c:151)
  CPU: 19 PID: 19426 Comm: trinity-c19 Tainted: G        W     3.14.0-rc7-next-20140325-sasha-00014-g9476368-dirty #274
  RIP:  strlcpy (lib/string.c:388 lib/string.c:151)
  Call Trace:
   ocfs2_cluster_connect (fs/ocfs2/stackglue.c:350)
   ocfs2_cluster_connect_agnostic (fs/ocfs2/stackglue.c:396)
   user_dlm_register (fs/ocfs2/dlmfs/userdlm.c:679)
   dlmfs_mkdir (fs/ocfs2/dlmfs/dlmfs.c:503)
   vfs_mkdir (fs/namei.c:3467)
   SyS_mkdirat (fs/namei.c:3488 fs/namei.c:3472)
   tracesys (arch/x86/kernel/entry_64.S:749)

akpm: this patch probably disables the feature.  A temporary thing to
avoid triviel oopses.

Signed-off-by: Sasha Levin <[email protected]>
Cc: Goldwyn Rodrigues <[email protected]>
Cc: Mark Fasheh <[email protected]>
Cc: Joel Becker <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>