Subject: Re: [net-next PATCH v2 1/1] net sched actions: skbedit add support for mod-ing skb pkt_type

From: Daniel Borkmann <[email-masked]>
Date: Mon, 13 Jun 2016 10:00:27 +0200

Hi Jamal,

On 06/12/2016 11:24 PM, Jamal Hadi Salim wrote:
> From: Jamal Hadi Salim <[email-masked]>
>
> Extremely useful for setting packet type to host so i dont
> have to modify the dst mac address using pedit (which requires
> that i know the mac address)
>
> Signed-off-by: Jamal Hadi Salim <[email-masked]>

I'm wondering if this is a good idea, I was thinking about something
like this as well some time ago. So far pkt_type is just exposed as
read-only to user space right now and I'm a bit worried that when we
allow to set it arbitrarily, then this could lead to hard to debug
issues since skb->pkt_type is used in a lot of places with possibly
different assumptions and applications now need to mistrust the kernel
whether skb->pkt_type was actually what the kernel itself set in the
first place or skbedit with possibly some nonsense value (like rewriting
PACKET_OUTGOING into PACKET_LOOPBACK, etc). Did you audit that this
is safe?

Thanks,
Daniel