[tor-bugs] #25870 [Core Tor/Tor]: Fix vanguard restrictions

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#25870: Fix vanguard restrictions
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 Reporter:  mikeperry     |          Owner:  (none)
     Type:  defect        |         Status:  needs_review
 Priority:  Medium        |      Milestone:  Tor: 0.3.4.x-final
Component:  Core Tor/Tor  |        Version:
 Severity:  Normal        |     Resolution:
 Keywords:                |  Actual Points:
Parent ID:  #25546        |         Points:
 Reviewer:  asn           |        Sponsor:
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Comment (by asn):

 Hey Mike, can you explain how the branch prevents Tor from building `A - B
 - A` paths as it claims?

 IIUC, commit `4b61ba2a98` starts allowing `A - B - A` paths since it
 removes the guard-to-exit restriction. Then commit `ac348ffbae` modifies
 `build_middle_exclude_list()` which should only exclude possibilities for
 the ''middle nodes'', hence blocking paths like `A - A - B` or `A - B -
 B`. Am I wrong?

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/25870#comment:4>
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