netdev - Re: [PATCH net 2/2] udp: restrict offloads to one namespace

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Date:	Thu, 17 Dec 2015 18:40:12 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Tom Herbert <tom@...bertland.com>
Cc:	David Miller <davem@...emloft.net>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH net 2/2] udp: restrict offloads to one namespace

On 17.12.2015 18:32, Tom Herbert wrote:
> On Thu, Dec 17, 2015 at 12:49 AM, Hannes Frederic Sowa
> <hannes@...essinduktion.org> wrote:
>> With user namespaces a normal user can start a new network namespace
>> with all privileges and thus add new offloads, letting the other stack
>> interpret this garbage. Because the user namespace can also add
>> arbitrary ip addresses to its interface, solely matching those is not
>> enough.
>>
>> Tom any further comments?
>>
> I still don't think this addresses the core problem. If we're just
> worried about offloads being added in a user namespace that conflict
> with the those in the root space, it might be just as easy to disallow
> setting offloads except in default namespace.

I am fine with that solution, too.

> [...]
>
> To address this in the host stack the solution is pretty
> straightforward, we need to decide that the packet is going to be
> received before applying any offloads. Essentially we want to do an
> early_demux _really_ early. If we demux and get UDP socket for
> instance, then the protocol specific GRO function can be retrieved
> from the socket. So this will work with single listener port like
> encaps do today,  and also if encapsulation is being used over a
> connected socket. This also works if we want to support a user defined
> GRO function like I mentioned we might want to do for QUIC etc.

An approximation can be done, but I don't think it is feasible to
implement this kind of checks across namespace borders, ip rules and
netfilter rulesets, which could all change the outcome of the process.

Bye,
Hannes


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