[tor-bugs] #32794 [Core Tor/Tor]: improve OOS (out-of-sockets) handler victim selection and more

[Tor Bug Tracker & Wiki]

#32794: improve OOS (out-of-sockets) handler victim selection and more
--------------------------+------------------------------------
 Reporter:  starlight     |          Owner:  (none)
     Type:  defect        |         Status:  needs_review
 Priority:  Medium        |      Milestone:  Tor: 0.4.3.x-final
Component:  Core Tor/Tor  |        Version:  Tor: 0.4.2.5
 Severity:  Normal        |     Resolution:
 Keywords:                |  Actual Points:
Parent ID:                |         Points:
 Reviewer:  nickm         |        Sponsor:
--------------------------+------------------------------------

Comment (by nickm):

 Hi! I have some comments on the code, but before I get to them, we should
 talk about the approach.

 The new algorithm seems to be

 1. Always keep OR-to-OR connections; always keep directory connections.
 Only inspect client-to-guard and exit connections.

 2. When discarding connections, discard those that were created most
 recently.

 Is that right?  If so, I wonder if there is some way that attacker can
 exploit this by making a bunch of directory connections, if our directory
 port is open.  Maybe we should consider CONN_TYPE_DIR as well.

 I also wonder if the attacker can reduce our number of available sockets
 by simply attempting a socket exhaustion attack.  We'll kill off some of
 their connections, but we won't kill them all.  If the attacker preserves
 the ones that we don't kill, they will always survive instead of any newer
 connections that we receive in the future.  Can we do any better than
 this?

 (Once we're in agreement here, we should describe the algorithm we want to
 follow in a patch to tor-spec.txt, so that the correct behavior is
 documented.)

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/32794#comment:3>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online