  We present a nonlinear model of self-consistent Galactic halo, where the
processes of cosmic ray (CR) propagation and excitation/damping of MHD waves
are included. The MHD-turbulence, which prevents CR escape from the Galaxy, is
entirely generated by the resonant streaming instability. The key mechanism
controlling the halo size is the nonlinear Landau (NL) damping, which
suppresses the amplitude of MHD fluctuations and, thus, makes the halo larger.
The equilibrium turbulence spectrum is determined by a balance of CR excitation
and NL damping, which sets the regions of diffusive and advective propagation
of CRs. The boundary $z_{cr}(E)$ between the two regions is the halo size,
which slowly increases with the energy. For the vertical magnetic field of
$\sim 1~\mu G$, we estimate $z_{cr} \sim 1$ kpc for GeV protons. The derived
proton spectrum is in a good agreement with observational data.
