Is it possible to configure a system such that a certain non-privileged user can only access the net through a VPN? I have an ethernet connection eth0 and a VPN network connection ppp0, and I'd like for the non-privileged user to be able to use networking through ppp0 but not eth0. It's easy enough to block the user from using eth0, telling iptables:

iptables -A OUTPUT -o eth0 -m owner --uid-owner [nonprivileged-username] -j REJECT

However, while that blocks the user from sending outbound traffic from eth0, I can't configure the user to use ppp0 instead. This user can't modify the routing table, since it is a nonprivileged user, and I'd prefer not to have to make global modifications to the routing table anyway since other users on the system still need to use eth0.

Thanks!