I think you'll have to play around with symlinks and permissions. Off the top of my head, I think that if you chroot them to their home directory and symlink /usr/share/data to the home directory, they shouldn't be able to get into that and cd up from it. However, that's not tested.
In the case where I've set up similar things, we used Linux and Linux ACL's, so I can't be sure if the advice I give above will work or not.
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