If LISTXATTRS is sent with a correct cookie but a small maxcount,
this could lead function nfsd4_listxattr_validate_cookie to
return NFS4ERR_BAD_COOKIE. If maxcount = 20, then second check
on function gives RHS = 3 thus any cookie larger than 3 returns
NFS4ERR_BAD_COOKIE.
There is no need to validate the cookie on the return XDR buffer
since attribute referenced by cookie will be the first in the
return buffer.
Fixes: 23e50fe3a5e6 ("nfsd: implement the xattr functions and en/decode logic") Signed-off-by: Jorge Mora <mora@netapp.com> Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>