  Ghosh and Sarnak have studied integral points on surfaces defined by an
equation x^2+y^2+z^2-xyz= m over the integers. For these affine surfaces, we
systematically study the Brauer group and the Brauer-Manin obstruction to the
integral Hasse principle. We prove that strong approximation for integral
points on any such surface, away from any finite set of places, fails, and
that, for m\neq 0, 4, the Brauer group does not control strong approximation.
