[tor-bugs] #15515 [Tor]: Don't allow multiple INTRODUCE1s on the same circuit

[Tor Bug Tracker & Wiki]

#15515: Don't allow multiple INTRODUCE1s on the same circuit
--------------------+------------------------------------
 Reporter:  asn     |          Owner:
     Type:  defect  |         Status:  new
 Priority:  normal  |      Milestone:  Tor: 0.2.7.x-final
Component:  Tor     |        Version:
 Keywords:          |  Actual Points:
Parent ID:          |         Points:
--------------------+------------------------------------
 Currently, it seems like clients are able to send multiple INTRODUCE1
 cells to the IP. The result is that many INTRODUCE2 cells reach the HS,
 which means that the HS will try to establish multiple rendezvous
 circuits.

 This gives a better position to attackers who want to flood a HS with
 rendezvous circuits (like #15463), since with a single circuit they can
 cause hundreds of rendezvous.

 We should fix this in the IP-side, by closing the circuit after sending
 the `INTRODUCE_ACK` to the client. An alternate behavior, is to change the
 state of the circuit after `INTRODUCE1` is received and close it if more
 such cells are received.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/15515>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online