[tor-bugs] #23989 [Core Tor/Tor]: entry_guards_update_all() will pretend to update primaries even if sampled set is empty

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#23989: entry_guards_update_all() will pretend to update primaries even if sampled
set is empty
-------------------------+-------------------------------------------------
     Reporter:  asn      |      Owner:  (none)
         Type:  defect   |     Status:  new
     Priority:  Medium   |  Milestone:  Tor: 0.3.2.x-final
    Component:  Core     |    Version:  Tor: 0.3.0.1-alpha
  Tor/Tor                |   Keywords:  tor-guard, tor-bridge, tor-client,
     Severity:  Normal   |  030-backport, 031-backport
Actual Points:           |  Parent ID:  #23862
       Points:           |   Reviewer:
      Sponsor:           |
-------------------------+-------------------------------------------------
 `entry_guards_update_all()` is used to update all the various sets of the
 guard subsystem, and then make the list of primary guards.

 The first list that needs to be made is the sampled set in
 `sampled_guards_update_from_consensus()`. However ,that function is a NOP
 if we are missing a live consensus.

 The problem here is that `entry_guards_update_all()` will not notice that
 the sampled set was never initialized and will happily move forward into
 making the list of primary guards from a non-existent sampled set which
 will fail. It will also set `gs->primary_guards_up_to_date` and other
 parts of the subsystem will think that there is actually a primary guard
 list and will not initialize it (e.g. `select_entry_guard_for_circuit()`).

 We should probably not allow the primary guard list etc. to be done if we
 failed to initialize our sampled set. Perhaps we could move the
 `live_consensus_is_missing()` check from
 `sampled_guards_update_from_consensus()` to `entry_guards_update_all()`.

 '''I don't think that this can cause serious issues''' because we will
 eventually regenerate our primary guard list when we finally fetch a live
 consensus.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/23989>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
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