[tor-bugs] #18929 [Core Tor/Tor]: Fix selection of directories with non-preferred address families

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#18929: Fix selection of directories with non-preferred address families
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 Reporter:  teor                                 |          Owner:
     Type:  defect                               |         Status:
 Priority:  Medium                               |  needs_review
Component:  Core Tor/Tor                         |      Milestone:  Tor:
 Severity:  Normal                               |  0.2.8.x-final
 Keywords:  must-fix-before-028-rc,              |        Version:  Tor:
  TorCoreTeam201605                              |  0.2.8.1-alpha
Parent ID:  #18483                               |     Resolution:
 Reviewer:  isis,nickm                           |  Actual Points:  2 hours
                                                 |         Points:  small
                                                 |        Sponsor:
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Old description:

> In #17840 in 0.2.8.1-alpha, we sometimes fail to fall back to directories
> with addresses in non-preferred IP families:
> * we didn't identify relays that we could fall back to correctly;
> * we incorrectly assumed that every node would have an IPv4 address -
> this doesn't apply to bridges;
> * we counted relays when we had already fallen back to non-preferred
> addresses.
>
> This likely affected bridge clients with IPv4 bridges, and clients in
> small networks.

New description:

 In #17840 in 0.2.8.1-alpha, we sometimes fail to fall back to directories
 with addresses in non-preferred IP families:
 * we didn't identify relays that we could fall back to correctly;
 * we incorrectly assumed that every node would have an IPv4 address~~ -
 this doesn't apply to bridges~~;
 * we counted relays when we had already fallen back to non-preferred
 addresses.

 This likely affected ~~bridge clients with IPv4 bridges, and~~ clients in
 small networks.

--

Comment (by teor):

 Wow, you're right, let's do it the simple way - delete the bad check:
 bug18929-v3

 (I thought I was saving client speed at the cost of complexity. For most
 clients, this would have imposed more checks on every directory for no
 benefit, and for clients where it mattered, I didn't have actual
 performance figures.)

 I will need to rebuild a simpler #18483 branch now there's no dependency
 between them.

 For the record:
 > NM2 For router_has_non_preferred_address_node -- an unlisted bridge has
 a node_t, but does not have a routerstatus. Can this function ever get
 called on a bridge? Do we care?

 This function never gets called on a bridge, as
 directory_get_from_dirserver handles bridges.
 So this bug never affected bridges or bridge clients, sorry, isis!

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/18929#comment:12>
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