[tor-bugs] #23524 [Core Tor/Tor]: Avoid crashing when we ask for running bridges, but UseBridges is 0

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#23524: Avoid crashing when we ask for running bridges, but UseBridges is 0
---------------------------------------------+-----------------------------
 Reporter:  teor                             |          Owner:  teor
     Type:  defect                           |         Status:
                                             |  needs_revision
 Priority:  Medium                           |      Milestone:  Tor:
                                             |  0.3.2.x-final
Component:  Core Tor/Tor                     |        Version:  Tor:
                                             |  0.3.0.1-alpha
 Severity:  Normal                           |     Resolution:
 Keywords:  dos-resistance, review-group-26  |  Actual Points:  0.1
Parent ID:  #24367                           |         Points:  0.1
 Reviewer:                                   |        Sponsor:
---------------------------------------------+-----------------------------
Changes (by nickm):

 * status:  merge_ready => needs_revision
 * milestone:  Tor: 0.3.1.x-final => Tor: 0.3.2.x-final


Comment:

 I spoke too soon -- the unit tests break when I merge this branch:

 {{{
   FAIL src/test/test_entrynodes.c:618: assert(gs_br OP_EQ NULL):
 0x5585741f34b0 vs (nil)entrynodes/parse_from_state_full:
   [parse_from_state_full FAILED]
 entrynodes/get_guard_selection_by_name:
   FAIL src/test/test_entrynodes.c:802: assert(gs3 ==
 get_guard_selection_info())
   [get_guard_selection_by_name FAILED]

   FAIL src/test/test_entrynodes.c:2258: assert(r OP_EQ 0): -1 vs
 0entrynodes/drop_guards:
   [drop_guards FAILED]
 entrynodes/outdated_dirserver_exclusion:
   FAIL src/test/test_entrynodes.c:2777: expected log to contain "No
 primary or confirmed guards available."  Captured logs:
     1. info: "Not setting md restriction: only 0 usable guards.\n"
     2. info: "Trying to sample a reachable guard: We know of 0 in the
 USABLE_FILTERED set.\n"
     3. info: "  (That isn\'t enough. Trying to expand the sample.)\n"
     4. info: "Expanding the sample guard set. We have 0 guards in the
 sample, and 0 eligible guards to extend it with.\n"
     5. info: "Not expanding the guard sample any further; just ran out of
 eligible guards\n"
     6. info: "  (After filters [b], we have 0 guards to consider.)\n"
     7. info: "Trying to sample a reachable guard: We know of 0 in the
 USABLE_FILTERED set.\n"
     8. info: "  (That isn\'t enough. Trying to expand the sample.)\n"
     9. info: "Expanding the sample guard set. We have 0 guards in the
 sample, and 0 eligible guards to extend it with.\n"
    10. info: "Not expanding the guard sample any further; just ran out of
 eligible guards\n"
    11. info: "  (After filters [7], we have 0 guards to consider.)\n"
    12. info: "Absolutely no sampled guards were available. Marking all
 guards for retry and starting from top again.\n"
    13. info: "No router found for microdescriptor fetch; falling back to
 dirserver list.\n"
    14. notice: "While fetching directory info, no running dirservers
 known. Will try again later. (purpose 19)\n"

   [outdated_dirserver_exclusion FAILED]
 4/1031 TESTS FAILED. (31 skipped)
 }}}

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/23524#comment:13>
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