netdev - Re: [PATCH net,stable] tun: fix vlan packet truncation

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Date:   Tue, 17 Apr 2018 10:08:29 +0200
From:   Bjørn Mork <bjorn@...k.no>
To:     Jason Wang <jasowang@...hat.com>
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH net,stable] tun: fix vlan packet truncation

Jason Wang <jasowang@...hat.com> writes:

> Good catch,

Thanks.  I guess I am "lucky" as I apparently use configs no one else
are using, and therefore often experience breakage ;-)  

I have been using tagged interfaces over tap for an occasional virtual
"lab" of kvm machines for years. It's a simple way to have a flexible
netowrk between host and virtual machine.  So v4.16 broke my "lab". I'm
sorry it took me a while before I had time to investigate why.

> but I still think we should do the truncation in
> run_ebpf_filter to match the behavior socket ebpf filter.

Haven't looked at that code.  But I'd like to point out that any length
adjustments should be done next to the code adding or removing data.
Doing data and length modifications in different funtions is either a
bug, or a bug bound to happen.

Bjørn