[zeromq-dev] Vulnerability of devices to incoming messages

[MinRK]

On Wed, Aug 11, 2010 at 11:37, Matt Weinstein <matt_weinstein at yahoo.com>wrote:

> Here's one argument against this:
>
> If you forward a malformed stream to an XREP you have a design flaw, and
> you should fix it.  Proper input checking should be done.
>

The issue is that the builtin devices forward messages without checking. The
only checking happens on the client side, and that only checks whether it is
a valid message sent to the input socket, not that the message will be valid
on its way out of the output socket.

My code doesn't ever cause the error, but all a malicious code needs is
access to the non-XREP port, and they can trivially crash the entire process
containing the device, and there's nothing my code can do about it short of
protecting the port itself.


>
> Making the traffic disappear without any indication will make error
> detection and correction much more difficult, especially when dealing with
> these exotic socket types.
>

I agree that debugging your XREP code will be more difficult if you do this,
but that's already tricky, since if you have a wrong IDENT, your messages
silently vanish already.


>
> If you do decide to implement the non-strict form, it is still an error IMO
> and should return an error indication, even if it does not cause massive
> destruction within the environment.
>

Returning an error code rather than raising SIGABRT is a good model.  That
allows prudent* user code with an XREP socket to notice the error, but
protects the devices from this vulnerability, as long as they don't have
'assert(rc!=0);' code, which they currently do.

*by prudent, I mean the traditional:
rc = xrep.send(msg);
if (rc != 0){
   handle_it();
}


>
> Thanks,
>
> Best,
> Matt
>
>
> On Aug 11, 2010, at 2:23 PM, MinRK wrote:
>
> That does indeed fix the vulnerability in my code, thanks!
>
> Is it better for zmq in general, though, for xrep.send('msg') to silently
> fail, rather than raise? It's good for me, but I can imagine others having
> objections.
>
> I suppose this does better match the behavior of having an unmatched
> identity prefix on a valid message on an xrep, which just vanishes into the
> aether, right?
>
> -MinRK
>
> On Wed, Aug 11, 2010 at 04:03, Pieter Hintjens <ph at imatix.com> wrote:
>
>> Hi Benjamin,
>>
>> Here's a patch for xrep.cpp that silently drops the message if it's
>> malformed.  This will make the standard devices robust against the
>> vulnerability you explained.
>>
>> I've tested it and it works for your test case.  Could you confirm it
>> works, then I'll commit the change to master.
>>
>> http://gist.github.com/518810
>>
>> -Pieter
>>
>> On Tue, Aug 10, 2010 at 7:30 PM, MinRK <benjaminrk at gmail.com> wrote:
>> > It is posted here:
>> > http://github.com/zeromq/zeromq2/issues/issue/46
>> > with accompanying gist for reproducing the issue.
>> >
>> > -MinRK
>> > On Tue, Aug 10, 2010 at 01:25, Pieter Hintjens <ph at imatix.com> wrote:
>> >>
>> >> Benjamin,
>> >>
>> >> Could you provide a minimal test case that reproduces the problem, and
>> >> perhaps file an issue on the github tracker, thanks.
>> >>
>> >> -Pieter
>> >>
>> >> On Tue, Aug 10, 2010 at 8:34 AM, MinRK <benjaminrk at gmail.com> wrote:
>> >> > Hello,
>> >> > I'm using ZMQ devices for parallel computing in IPython.  One of our
>> >> > devices
>> >> > is a Queue with XREQ on one side and XREP on the other. This model,
>> like
>> >> > any
>> >> > device where one socket requires an IDENT prefix (XREP), and the
>> other
>> >> > does
>> >> > not prepend a message (anything other than XREP), is vulnerable to
>> >> > invalid
>> >> > messages. If the socket that is not XREP receives a single message,
>> that
>> >> > will be relayed to the XREP as a message with routing IDENTITY but no
>> >> > content. This fails an assertion, and triggers SIGABRT, bringing down
>> >> > the
>> >> > entire process.
>> >> > It is a security concern for us that _incoming_ messages have the
>> >> > ability to
>> >> > crash the device process. Are there any standard models or plans for
>> ZMQ
>> >> > devices that can survive invalid messages like this?
>> >> > -MinRK
>> >> > _______________________________________________
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>> >> >
>> >> >
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