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

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Message-ID: <CALx6S363K9DXbPq0VCd8+AW-5v3oz+AXMnDF5-BBarh-WTsUGA@mail.gmail.com>
Date:	Thu, 17 Dec 2015 10:10:50 -0800
From:	Tom Herbert <tom@...bertland.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
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 Thu, Dec 17, 2015 at 9:40 AM, Hannes Frederic Sowa
<hannes@...essinduktion.org> wrote:
> 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.
>
For receive offloads we don't need to worry about checking other namespaces.

> Bye,
> Hannes
>
>
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