[tor-bugs] #15518 [Core Tor/Tor]: Tor considers routers in the same IPv6 /16 to be "in the same subnet"

[Tor Bug Tracker & Wiki]

#15518: Tor considers routers in the same IPv6 /16 to be "in the same subnet"
-------------------------------------------------+-------------------------
 Reporter:  isis                                 |          Owner:  (none)
     Type:  defect                               |         Status:  new
 Priority:  High                                 |      Milestone:  Tor:
                                                 |  unspecified
Component:  Core Tor/Tor                         |        Version:
 Severity:  Normal                               |     Resolution:
 Keywords:  ipv6, path, path-bias, tor-client    |  Actual Points:
  easy                                           |
Parent ID:  #24393                               |         Points:  1
 Reviewer:                                       |        Sponsor:
-------------------------------------------------+-------------------------

Comment (by teor):

 The current code in addrs_in_same_network_family() calls
 tor_addr_compare_masked() to compare all addresses by /16.

 You need to add more calls to tor_addr_compare_masked() in
 addrs_in_same_network_family() so that:
 * if the family of a1 is AF_INET, it uses /16 for IPv4
 * if the family of a1 is AF_INET6 and tor_addr_is_v4(a1), it uses /112 for
 an IPv6-mapped IPv4 address (96 bits for the v4 map and 16 for IPv6)
 * otherwise, it is native IPv6, and it uses /32.

 I realise this is a change from what I said above, I just read
 tor_addr_compare_masked() and it's more complicated than I thought.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/15518#comment:27>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online