netdev - Re: [Patch net-next] net: make neigh tables per netns

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Date:	Mon, 30 Jun 2014 20:15:18 +0200
From:	Jesper Dangaard Brouer <brouer@...hat.com>
To:	ebiederm@...ssion.com (Eric W. Biederman)
Cc:	brouer@...hat.com, Cong Wang <xiyou.wangcong@...il.com>,
	David Miller <davem@...emloft.net>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	Patrick McHardy <kaber@...sh.net>,
	Stephen Hemminger <stephen@...workplumber.org>,
	Cong Wang <cwang@...pensource.com>,
	Stefan Bader <stefan.bader@...onical.com>,
	stephane.graber@...onical.com, chris.j.arges@...onical.com,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>
Subject: Re: [Patch net-next] net: make neigh tables per netns


On Fri, 27 Jun 2014 22:12:52 -0700 ebiederm@...ssion.com (Eric W. Biederman) wrote:
> Cong Wang <xiyou.wangcong@...il.com> writes:
> > On Thu, Jun 26, 2014 at 3:44 PM, David Miller <davem@...emloft.net> wrote:
> >>
[...]
> >
> > Hmm, I did overlook the potential DOS problem. But hold on, isn't
> > IP fragments have the same problem? The fragment queues are per
> > netns, and the thresh is per netns as well, we will eventually have
> > memory pressure as well.
> 
> Interesting.  It does look like ip fragments are susceptible that way.

For IP fragments we have per netns mem-limit and LRU-list, but all
netns share the same hash table, which have its own DoS potential.

And argh! - we have a hardcoded INETFRAGS_MAXDEPTH=128, which can be
used for (slow) DoS of IP frags if enough netns are created.

https://git.kernel.org/cgit/linux/kernel/git/davem/net-next.git/tree/net/ipv4/inet_fragment.c#n344

Introduced by commit 5a3da1fe9 ("inet: limit length of fragment queue
hash table bucket lists").
-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Sr. Network Kernel Developer at Red Hat
  Author of http://www.iptv-analyzer.org
  LinkedIn: http://www.linkedin.com/in/brouer
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