netdev - Re: [PATCH net] netlink: preserve netlink pkt_type on dev_queue_xmit

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Date:	Sat, 12 Apr 2014 17:02:05 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	dborkman@...hat.com
Cc:	netdev@...r.kernel.org, darkjames-ws@...kjames.pl
Subject: Re: [PATCH net] netlink: preserve netlink pkt_type on
 dev_queue_xmit_nit

From: Daniel Borkmann <dborkman@...hat.com>
Date: Fri, 11 Apr 2014 20:25:29 +0200

> In dev_queue_xmit_nit(), we unconditionally overwrite
> the pkt_type of the new skb clone to PACKET_OUTGOING,
> thus in packet sockets, we always propagate this to
> sll_pkttype member of struct sockaddr_ll.
> 
> Hence, probe for skb_nit_type_netlink() and in case
> we tap on a non-netlink socket, overwrite the setting
> to PACKET_OUTGOING just as before. I think we can mark
> the _non_-netlink sockets as likely since i) we don't
> expect such heavy load in netlink messages as we do
> with network packets, and ii) tapping on netlink
> messages is rather to be considered a rare event
> compared to tapping on network packets.
> 
> I have tested this with capturing on latest netsniff-ng
> and propagation works fine. While at it, we also fixed
> up the comment style and added two cases where their
> conditions are to be considered unlikely() as well.
> 
> Signed-off-by: Daniel Borkmann <dborkman@...hat.com>

I really don't like the idea of treating some packets that go out of
dev_queue_xmit_nit() as one type, and others of another type.

Because dammit, if the packet is going through this function it very
much is PACKET_OUTGOING.

It's outgoing to your special netlink tap device in this case right?

Sorry, I really don't want to apply this patch, and you haven't even
stated 1) what problem this actually causes and 2) why you cannot deal
around it in userspace.
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