[tor-bugs] #14881 [Core Tor/Tor]: incorrect defaults when producing bandwidth-weights line in directory footer

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#14881: incorrect defaults when producing bandwidth-weights line in directory
footer
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 Reporter:  robgjansen                           |          Owner:
     Type:  defect                               |  robgjansen
 Priority:  Medium                               |         Status:
Component:  Core Tor/Tor                         |  needs_revision
 Severity:  Normal                               |      Milestone:  Tor:
 Keywords:  027-triaged-1-in, 028-triaged,       |  0.2.9.x-final
  pre028-patch, TorCoreTeam201604, tor-          |        Version:  Tor:
  sponsorU-orphan                                |  0.2.7
Parent ID:                                       |     Resolution:
 Reviewer:  mikeperry                            |  Actual Points:
                                                 |         Points:  medium
                                                 |        Sponsor:
                                                 |  SponsorU-can
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Changes (by mikeperry):

 * status:  needs_review => needs_revision


Comment:

 First thoughts: Does this run without printing out additional errors?
 networkstatus_check_weights() verifies that the linear algebra has a
 consistent solution and will cause a warn to be emitted if not, and the
 weights will still be omitted. At minimum, for full correctness I think we
 need to initialize T to 4 here, if we initialize all other weights to 1.
 Technically we're also introducing a slight inaccuracy by this method of
 initialization, as well (since we're giving every node class a tiny bit of
 weight that isn't actually there).

 It may also be the case that we were within a rounding error of
 correctness, and so this ran OK.

 I think this might mean that it would be simplest for this change to apply
 to testing networks only. Perhaps we just have a testing network check at
 the top of networkstatus_compute_bw_weights_v10() that sets weights to 1
 only if it is a testing network and they are zero.

 Give me a second and I will attach an alternate (untested) patch just for
 testing networks.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/14881#comment:22>
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