netdev - Re: [RFD] L2 Network namespace infrastructure

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Date:	Sat, 23 Jun 2007 22:19:34 +0200
From:	Carl-Daniel Hailfinger <c-d.hailfinger.devel.2006@....net>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	Patrick McHardy <kaber@...sh.net>, Jeff Garzik <jeff@...zik.org>,
	YOSHIFUJI Hideaki <yoshfuji@...ux-ipv6.org>,
	netdev@...r.kernel.org, jamal <hadi@...erus.ca>,
	Linux Containers <containers@...ts.osdl.org>,
	Ben Greear <greearb@...delatech.com>,
	Stephen Hemminger <shemminger@...ux-foundation.org>,
	David Miller <davem@...emloft.net>
Subject: Re: [RFD] L2 Network namespace infrastructure

On 23.06.2007 19:19, Eric W. Biederman wrote:
> Patrick McHardy <kaber@...sh.net> writes:
> 
>> Eric W. Biederman wrote:
> 
>>> Depending upon the data structure it will either be modified to hold
>>> a per entry network namespace pointer or it there will be a separate
>>> copy per network namespace.  For large global data structures like
>>> the ipv4 routing cache hash table adding an additional pointer to the
>>> entries appears the more reasonable solution.
>>
>> So the routing cache is shared between all namespaces?
> 
> Yes.  Each namespaces has it's own view so semantically it's not
> shared.  But the initial fan out of the hash table 2M or something
> isn't something we want to replicate on a per namespace basis even
> assuming the huge page allocations could happen.
> 
> So we just tag the entries and add the network namespace as one more
> part of the key when doing hash table look ups.

Can one namespace DoS other namespaces' access to the routing cache?
Two scenarios come to mind:
* provoking hash collisions
* lock contention (sorry, haven't checked whether/how we do locking)

Regards,
Carl-Daniel
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