netdev - Re: [PATCHv1 net-next 0/5] netlink: mmap: kernel panic and some issues

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Date:	Tue, 08 Sep 2015 22:59:57 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	daniel@...earbox.net
Cc:	chamaken@...il.com, netdev@...r.kernel.org, fw@...len.de
Subject: Re: [PATCHv1 net-next 0/5] netlink: mmap: kernel panic and some
 issues

From: Daniel Borkmann <daniel@...earbox.net>
Date: Mon, 07 Sep 2015 16:54:46 +0200

> On 08/17/2015 11:02 PM, David Miller wrote:
> ...
>> I would seriously rather see us do an expensive full copy of the SKB
>> than to have traffic which is unexpectedly invisible to taps.
> 
> I've been looking into this issue a bit further, so the copy for the
> tap seems doable, but while further going through the code to find
> similar
> issues elsewhere, and doing some experiments, it looks like we write
> shared info also in some edge-cases of upcalls such as nfqueue or ovs
> when mmaped netlink is used for rx. I did a test with nfqueue using
> the libmnl mmap branch [1].

Honestly if it's something isolated to something like nf_queue it can
be contained to just being a special fix there.

nf_queue is usually very special and needs hacks to handle things
properly since it acts as an "escape" point for various SKB things.

But if it's in OVS too....

I guess we need a more generic fix.
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