[tor-bugs] #12377 [Tor]: get_interface_address6() behaviour iff all interface addresses are internal

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#12377: get_interface_address6() behaviour iff all interface addresses are internal
-------------------------+-------------------------------------------------
     Reporter:  rl1987   |      Owner:
         Type:  defect   |     Status:  new
     Priority:  normal   |  Milestone:  Tor: 0.2.6.x-final
    Component:  Tor      |    Version:  Tor: unspecified
   Resolution:           |   Keywords:  tor-relay 026-triaged-1
Actual Points:           |  026-deferrable
       Points:           |  Parent ID:  #12376
-------------------------+-------------------------------------------------

Comment (by dgoulet):

 According to the comment, it's doing it's job but I'm starting to wonder
 if it's actually used right.

 {{{
 /** Set *<b>addr</b> to the IP address (if any) of whatever interface
  * connects to the Internet.
 }}}

 In connection.c, function {{{client_check_address_changed()}}}, it's used
 to get the "last interface ip" (which {{{get_interface_address6()}}}
 provides) and see if we've seen it before by looking into
 {{{outgoing_addrs}}}.

 Let's assume we have eth0 with one public IPv6 address, {{{1::cafe}}}

 {{{get_interface_address6()}}} will return that address since it fits the
 criteria and is the first valid public IP we see. So {{{outgoing_addrs}}}
 is updated with it and we live happily after. Lets add a second public
 usable IPv6, {{{2::cafe}}}.

 Now calling again {{{get_interface_address6()}}} should return the first
 valid one which is {{{1::cafe}}} (considering here alphabetical order)
 thus disregarding the new IP and making
 {{{client_check_address_changed()}}} failing to notice.

 Lots of pieces here, I might be missing a check thus need review :). If
 it's true, maybe the solution is to keep a list of all valid IPs of any
 usable interface and validate our state that way.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/12377#comment:4>
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