[tor-bugs] #12538 [Tor]: Make all relays automatically be dir caches

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#12538: Make all relays automatically be dir caches
-------------------------------------------------+-------------------------
 Reporter:  cypherpunks                          |          Owner:
     Type:  task                                 |         Status:
 Priority:  High                                 |  needs_revision
Component:  Tor                                  |      Milestone:  Tor:
 Severity:  Normal                               |  0.2.8.x-final
 Keywords:  tor-guard, tor-relay, prop237,       |        Version:  Tor:
  026-triaged-1, sebastian-review,               |  unspecified
  027-triaged-1-out, 028-triage, 028-triaged,    |     Resolution:
  mike-can, pre028-patch, TorCoreTeam201511      |  Actual Points:
Parent ID:                                       |         Points:
  Sponsor:                                       |  medium/large
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Changes (by dgoulet):

 * status:  needs_review => needs_revision


Comment:

 Here is an issue I found:

 * In src/or/or.h:

  `node_is_dir()` checks both the tunnelled support and dir_port which can
 by pass the fact that we shouldn't be advertising to be a dircache:
 {{{
 +    return ri->supports_tunnelled_dir_requests ||
 +           ri->dir_port > 0;
 }}}

  It's possible for `supports_tunnelled_dir_requests` to be 0, for instance
 if the Accounting is enabled and we've reached our max. But if we have a
 `DirPort`, it will bypass it and return 1. Seems to me that we maybe don't
 want to be used as a directory cache in that case?

  I think just testing `supports_tunnelled_dir_requests` is enough since it
 will be 1 if the DirPort is set and if the rest of the requirements are
 met (Accounting for instance).

 * Also fun fact, this below will make that a relay can opt-out of being an
 HSDir once it's accounting has reached the max or it's bandwitdh has
 changed dynamically (because of `router_should_be_directory_server()`):

 {{{
 +  return (router->wants_to_be_hs_dir &&
 +          router->supports_tunnelled_dir_requests &&
 ...
 }}}

  which could lead to client reachability issue (I think it won't be
 severe) if an HSDir can come and go at each consensus in a 24 hour period.
 _BUT_ it could also explain why we are seeing HSDir responding NOT_FOUND
 when they are suppose to have the descriptor because Accounting max was
 reached in that time period?...

 The rest lgtm;

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/12538#comment:83>
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