netdev - Re: [PATCH 5/5] net: Use netlink_ns_capable to verify the permisions of netlink messages

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Date:	Thu, 08 May 2014 17:52:03 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	stephen@...workplumber.org
Cc:	luto@...capital.net, jorge@...2.net, ebiederm@...ssion.com,
	vgoyal@...hat.com, ssorce@...hat.com, security@...nel.org,
	netdev@...r.kernel.org, serge@...lyn.com
Subject: Re: [PATCH 5/5] net: Use netlink_ns_capable to verify the
 permisions of netlink messages

From: Stephen Hemminger <stephen@...workplumber.org>
Date: Thu, 8 May 2014 14:21:21 -0700

> On Wed, 07 May 2014 19:45:14 -0400 (EDT)
> David Miller <davem@...emloft.net> wrote:
> 
>> From: Andy Lutomirski <luto@...capital.net>
>> Date: Wed, 7 May 2014 16:01:33 -0700
>> 
>> > On Wed, May 7, 2014 at 3:52 PM, David Miller <davem@...emloft.net> wrote:
>> >> From: Andy Lutomirski <luto@...capital.net>
>> >> Date: Wed, 7 May 2014 15:26:11 -0700
>> >>
>> >>> So what do we do?  Check permissions on connect and then use the
>> >>> cached result for send on a connected socket?  Check permitted caps
>> >>> instead of effective caps?
>> >>
>> >> It should create the socket after changing perms.
>> > 
>> > I agree that it should, but it doesn't, and if these patches get
>> > backported, things will break.  OTOH, if the patches don't get
>> > backported, things may still break, and we have a possibly rather
>> > severe unfixed vulnerability.
>> 
>> I think the kernel change is justified as the privilege allowance
>> that happened before was very much unintentional and as you've
>> shown us countless times a very real problem that we must fix.
> 
> One of the problems here is that Quagga may generate millions of
> netlink messages to change routes in response to link flap.
> Raising/lowering the permissions around each request would have
> a significant performance impact.

What we want to matter are the permissions the process had when the
socket was created/bound, after that you can drop privs and send
netlink requests as you like.
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