When a vlan interface is created, its if_output is set directly to the parent interface's if_output. This is fine in the normal case but has an unfortunate consequence if you end up with a certain combination of vlan and lagg interfaces. Consider you have a lagg interface with a single laggport member. When an interface is added to a lagg its if_output is set to lagg_port_output, which blackholes traffic from the normal networking stack but not certain frames from BPF (pseudo_AF_HDRCMPLT). If you now create a vlan with the laggport member (not the lagg interface) as its parent, its if_output is set to lagg_port_output as well. While this is confusing conceptually and likely represents a misconfigured system, it is not itself a problem. The problem arises when you then remove the lagg interface. Doing this resets the if_output of the laggport member back to its original state, but the vlan's if_output is left pointing to lagg_port_output. This gives rise to the possibility that the system will panic when e.g. bpf is used to send any frames on the vlan interface. Fix this by creating a new function, vlan_output, which simply wraps the parent's current if_output. That way when the parent's if_output is restored there is no stale usage of lagg_port_output. Reviewed by: rstone Differential Revision: D21209
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