netlink and user namespaces

Alexander Larsson alexl at
Fri May 29 12:18:27 UTC 2015

Now that I'm using a non-privileged user namespace for my desktop
sandboxing system all kind of network status things are breaking. The
reason for this is that they use netlink to enumerated interfaces, and
to verify that the replies are from the kernel (apparently anyone can
send anyone netlink messages) this code is verifying that the
SCM_CREDENTIAL sender of the netlink messages is uid 0.

For instance:

This obviously breaks when uid is not mapped (as it can't be in an
unprivileged user namespace), as uid will be overflowuid.

Is there any other way to check that a netlink message is from the

 Alexander Larsson                                            Red Hat, Inc 
       alexl at            alexander.larsson at 
He's an uncontrollable skateboarding farmboy trapped in a world he never 
made. She's a strong-willed renegade schoolgirl married to the Mob. They 
fight crime! 

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