VFS: nfs4acl_xattr: Ensure nfs4acl_get_blob() always gets a valid fsp pointer.

VFS: nfs4acl_xattr: Ensure nfs4acl_get_blob() always gets a valid fsp pointer.

This means adding a synthetic_pathref() call into the
nfs4acl_xattr version of SMB_VFS_GET_NT_ACL_AT() which
is the pathname-based ACL fetch call.

One place where this (smb_fname->fsp == NULL)
can happen is from open when checking parent
directory ACL - check_parent_access() currently
isn't always passed a smb_fname with a valid
fsp and check_parent_access() currently doesn't
open a pathref smb_fname->fsp itself (eventually
it should be passed in a pathref from the caller).

There are also a few other places inside smbd
that call smbd_check_access_rights() also without
a pathref fsp.

This check should be moved into the
callers inside smbd to ensure that smb_fname->fsp
is always valid here, and in a later patchset (not
part of this set) I will do just that.

Ultimately it may be possible to remove
pathname based SMB_VFS_GET_NT_ACL_AT(), this
requires further investigation.

But until then, we need this change.

Signed-off-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>