[tor-bugs] #4721 [Tor Relay]: Control socket available prior to generating DH modulus

Tor Bug Tracker & Wiki torproject-admin at torproject.org
Thu Dec 15 16:28:30 UTC 2011

#4721: Control socket available prior to generating DH modulus
 Reporter:  atagar     |          Owner:     
     Type:  defect     |         Status:  new
 Priority:  major      |      Milestone:     
Component:  Tor Relay  |        Version:     
 Keywords:             |         Parent:     
   Points:             |   Actualpoints:     
 The control socket is made available prior to a lengthy crypto operation
 which causes any input on to that socket to be ignored for something on
 the order of minutes. This in turn causes any controllers to either hang
 or need to implement timeouts for control responses (thankfully those
 haven't been necessary previously).

 If we could reorder the startup activity so the DH modulus generation
 happened before opening the control socket then that would be perfect.

 Flagging this as major since it's gonna cause a lot of sadness for first
 time tor users.

 irc context...
 08:13 < atagar> I'm trying to reproduce the arm issue mentioned on tor-
 talk and getting something odd from
 08:13 < atagar> Dec 15 08:09:59.000 [notice] Generating fresh dynamic DH
 modulus. This might take a while...
 08:13 < atagar> What does that log message mean? While that's going on
 controller requests hang (for instance, when I issue a PROTOCOLINFO I
 didn't get any response until I gave up and killed the process).
 Unfortunately this makes arm hang (and probably any other controller that
 tries to attach).
 08:13 < atagar> It would be nice if tor rejected the socket if it can't
 handle controller commands - shall I file a bug about this?
 08:14 < atagar> nickm: ^
 08:15 < nickm> atagar: It means that Tor is doing some cryptoish math to
 generate a modulus.
 08:15 < nickm> it will take a while.
 08:15 < nickm> it will happen on startup once, and will eat a bunch of cpu
 08:16 < atagar> Gotcha, thanks. Can it happen before opening a control
 08:19 < nickm> I don't know. It's possible, I think

Ticket URL: <https://trac.torproject.org/projects/tor/ticket/4721>
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