[tor-dev] Constraining Ephemeral Service Creation in Tor

[bancfc at openmailbox.org]

On 2016-09-29 08:38, teor wrote:
>> On 28 Sep 2016, at 07:59, bancfc at openmailbox.org wrote:
>> 
>> Hello, We are working on supporting ephemeral onion services in Whonix 
>> and one of the concerns brought up is how an attacker can potentially 
>> exhaust resources like RAM. CPU, entropy... on the Gateway (or system 
>> in the case of TAILS) by requesting an arbitrary number of services 
>> and ports to be created.
>> 
>> In our opinion, options in core Tor for setting a maximum number of 
>> services and ports per service seems the right way to go about it. 
>> Also rate limiting the requests (like you do with NEWNYM) would be a 
>> sensible thing to do.
>> 
>> What are your opinions about this?
> 
> I think this would be much better implemented in a control port filter.
> There are several existing control port filters.
> Do they have this feature?

None of them do.

> 
> Alternately, you should limit resources to the tor process using OS
> facilities. If you set an open file limit, this will constrain the
> number of hidden services.
> If it doesn't, or tor behaves badly when adding a hidden service with
> few file descriptors, file a bug against tor.

Thanks for the tip.

> 
> T
> 
> --
> Tim Wilson-Brown (teor)
> 
> teor2345 at gmail dot com
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> xmpp: teor at torproject dot org
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