modred team mailing list archive

[Scott Lawrence <bytbox@xxxxxxxxx>]

You're all missing the point.  I'm claiming that, properly
implemented, Modred should require no sandboxing outside of what is
necessary to implement it's logic.

So back to our good friends Alice, Bob, and Mallory.  Alice sends the
cluster (which means she directs it to the hub, but let's just
consider the cluster a big black box for now) some C source code.
This code does some strange stuff - lots of file i/o and memory
access.  What does the cluster do with this?

It links the program with its own special libraries.  Even inline
assembly has to call functions to interface with the hard drive and
allocate memory and such. Malicious code that gets submitted to the
server will be sanitized in this fashion.  The only problem I see is
with illegal memory access - but I suspect this will be dealt with,
because the cluster has to analyze what data the client program
accesses anyway...

Now Bob wants to compile and link his program on his own computer.
Fine.  He uses a different (smaller, incidentally) set of libraries.
These libraries don't intercept every call of malloc and stuff - those
are run on his computer.  But if he wants to access cluster data, he
has to use special functions.  And he can't actually run code on the
cluster.

Now what does Mallory do again?


On 12/28/09, Michael Cohen <gnurdux@xxxxxxxxx> wrote:
> Server-side I don't see an issue.  (java's, lua's,
>  >  javascript's, .NET/mono, some other random thing) is basically what
> I already said.  There are other sandboxing systems that are designed to
> work on x86 native code, such as vx32 (I think I mentioned that also).
> Many of these schemes (with the exception of vx32) have the advantage
> that they also automatically make the code cross-platform.  Even vx32 is
> supposedly portable to Windows, but nobody has done it yet and I have no
> idea if any of us have the expertise to.
>
> Frederic Koehler wrote:
>> As far as sandboxing, server-side you can presumably rely on the operating
>> system's sandboxes (per-user or perhaps some more elaborate mechanism like
>> FreeBSD's jails).
>>
>> But as soon as the cluster sends code out to clients, obviously there is a
>> big issue if we let them do whatever the hell they want. Just preventing
>> assembly or anything like that simply doesn't work in C/C++, (not to
>> mention
>> it would be suprisingly hard/irritating,) since the code could still
>> execute
>> the system-calls (you could try not linking against libc,too, but then you
>> _really_ have no portability :P).
>>
>> System-call controlling is possible, but is either pretty unportable (lots
>> of x86 assembly stuff) or slow-ish (virtual machines).
>>
>> That being said, if you completely seperate client-sendable code from
>> server-code, I think that allays a lot of the concerns. Requiring
>> client-sendable code to be written for some safe VM (java's, lua's,
>>  javascript's, .NET/mono, some other random thing) could avoid this. In
>> addition, client-sendable code would intentionally be written with
>> knowledge
>> of the sensitivity of the data it handles (i.e. not written at all if the
>> data is important).
>>
>> On Mon, Dec 28, 2009 at 7:49 PM, Michael Cohen <gnurdux@xxxxxxxxx> wrote:
>>
>>> I would still be happier if there were a sandbox, actually.  There are
>>> ways
>>> of getting around that sort of thing that are too complicated to prevent
>>> at
>>> the source level IMO.  For instance, you can use inline assembly.  So we
>>> block inline assembly.  That's all well and good, but now we've blocked
>>> people using legitimate assembly optimizations. Worse, what happens if
>>> they
>>> execute some shellcody stuff, allowing them to escape?  I don't really
>>> know
>>> how to block that at all.  On the other hand, a sandbox would not add
>>> much
>>> overhead since these tasks will most likely use lots of CPU time but few
>>> system calls or whatever.
>>>
>>>
>>> Michael Cohen
>>>
>>> Scott Lawrence wrote:
>>>
>>>> Ok, I'm going to build a prototype of my privacy model.  I'm not going
>>>> to implement the challenge-response stuff, I'll assume there's an
>>>> implementation of that and that it works.
>>>>
>>>> I think I've isolated the misunderstanding about the sandboxes.  You
>>>> don't submit binary code the the Modred cluster - you either submit
>>>> source, to be linked by the modred cluster with the relevant
>>>> libraries, or you link the code yourself with the libraries.  The
>>>> libraries that you would link with merely copy the program over to the
>>>> cluster, where it can be executed in a manner deemed fit by the code
>>>> there.
>>>>
>>>> I suppose you could say that that is a sandbox. ;-)
>>>>
>>>>
>>>> On 12/28/09, Michael Cohen <gnurdux@xxxxxxxxx> wrote:
>>>>
>>>>> If you read my email more carefully, you will see that I am not
>>>>> necessary objecting to Scott's suggestion.  I say that it is not
>>>>> necessary, but that it would be the only thing necessary to allow more
>>>>> problem-specific privacy tasks to be used.  The need for a sandbox is
>>>>> pretty simple.  If we make untrusted users able to ask for tasks, if
>>>>> they upload code, then I don't want it running unsandboxed on my
>>>>> computer.  Otherwise, their code could steal my files, wipe my
>>>>> harddisk,
>>>>> install Windows or do other undesirable things.  If it is sandboxed,
>>>>> then arbitary code can be executed safely, as long as we trust the
>>>>> sandbox.  Sandboxed environments are often also cross-platform, another
>>>>> plus, since they typically replace or intercept any kind of system
>>>>> call.
>>>>>
>>>>> Michael Cohen
>>>>>
>>>>> Scott Lawrence wrote:
>>>>>
>>>>>> Well, I'm glad someone expresses opinions I don't agree with...
>>>>>>
>>>>>> I think Mikey's objection to privacy concerns is that it's so
>>>>>> problem-specific, we can't reasonably expect to have a general
>>>>>> implementation.  But if the user specifies which parts of the data are
>>>>>> private, the Modred hub just has to be sure to divvy up tasks in a way
>>>>>> that gives those bits of information only to the trusted, dedicated
>>>>>> servers.
>>>>>>
>>>>>> For the purposes of clarity, I will be referring to dedicated servers
>>>>>> as simply "servers", and the central server as the "hub".
>>>>>>
>>>>>> I don't see the need for a sandbox.  Could you present some specific
>>>>>> attacks that a sandbox would fix?
>>>>>>
>>>>>>
>>>>>> On 12/28/09, Michael Cohen <gnurdux@xxxxxxxxx> wrote:
>>>>>>
>>>>>>> It seems to me that dealing with privacy concerns is an extremely
>>>>>>> problem-specific issue.  In any given case you need to work out how
>>>>>>> much
>>>>>>> you can give to people without letting private information leak, but
>>>>>>> the
>>>>>>> details vary greatly from problem to problem.  That isn't our
>>>>>>> business,
>>>>>>> and I don't think we should concern ourselves with it too much.  The
>>>>>>> way
>>>>>>> I see it there are two options:
>>>>>>>
>>>>>>> 1. make this designed for stuff without privacy concerns
>>>>>>>        I think this is both the easiest and the best option.  I don't
>>>>>>> really
>>>>>>> like the idea of a public, free service doing computations for an
>>>>>>> evil
>>>>>>> corporation anyway; if it's being done BY the public it should be
>>>>>>> done
>>>>>>> FOR the public.
>>>>>>>
>>>>>>> 2. add in a small amount of functionality designed to facilitate
>>>>>>> dealing
>>>>>>> with privacy concerns
>>>>>>>        At the level of this project, that would probably just be the
>>>>>>> controls
>>>>>>> on what data gets sent to what people.  There might be reasons for
>>>>>>> adding such controls anyway; some tasks could be designated for only
>>>>>>> "trusted" users.
>>>>>>>
>>>>>>> Either way I doubt that this will be a big issue.  I think maybe a
>>>>>>> bigger issue is how to run arbitrary code efficiently and securely.
>>>>>>>
>>>>>>> I see only a few solutions
>>>>>>>
>>>>>>>        Don't allow arbitrary code, but only a defined set of tasks.
>>>>>>>  Or,
>>>>>>> similarly, allow some "trusted" set of tasks, each separately ported
>>>>>>> to
>>>>>>> each platform (like boinc).
>>>>>>>
>>>>>>>        Use Java.  This lets us easily sandbox it and is
>>>>>>> cross-platform,
>>>>>>> but
>>>>>>> sacrifices a bit on efficiency.  Also, Java can be annoying (although
>>>>>>> other JVM languages would also work in this situation).
>>>>>>>
>>>>>>>        There are ways of running cross-platform, C/C++ code in a
>>>>>>> sandbox as
>>>>>>> well.  One possibility is to use LLVM, although the LLVM developers
>>>>>>> specifically say that LLVM is NOT designed to be used this way.
>>>>>>>  Another
>>>>>>> possibility is to use a sandboxed code system that works on multiple
>>>>>>> operating systems but only on x86.  This includes things like VX32,
>>>>>>> which is apparently portable to Windows, but hasn't been ported.  I
>>>>>>> don't know whether or not that sort of thing is within our abilities.
>>>>>>> Another option might be Google Native Client; that is designed to be
>>>>>>> used in a web browser but I don't know how hard it would be to "rip
>>>>>>> out"
>>>>>>> the sandboxing/cross-OS x86 code stuff.
>>>>>>>
>>>>>>> Michael Cohen
>>>>>>>
>>>>>>> _______________________________________________
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>>>>>>>
>>>>>>>
>>>>> _______________________________________________
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>>>>>
>>>>>
>>>>
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>>
>
>
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-- 
Scott Lawrence

Webmaster
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Montgomery Blair High School