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

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Message-ID: <CALx6S37VcT6fYjNuZ2YT5TqGK_FTbpcGoY5gKNYeoobrcTA8_Q@mail.gmail.com>
Date:	Thu, 17 Dec 2015 13:31:00 -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 12:33 PM, Hannes Frederic Sowa
<hannes@...essinduktion.org> wrote:
> 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.
>
I would opt for the latter then.

> Bye,
> Hannes
>
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