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

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Date:	Thu, 17 Dec 2015 21:33:32 +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 19:10, Tom Herbert wrote:
> 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.

That is true. Albeit for net-branch/stable I would still suggest either
this patch or restricting udp offloads just to the initial net namespace.

Bye,
Hannes

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