[tor-bugs] #12201 [Tor]: Don't weight by bandwidth when selecting among bridges

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#12201: Don't weight by bandwidth when selecting among bridges
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 Reporter:  asn                   |          Owner:
     Type:  defect                |         Status:  new
 Priority:  normal                |      Milestone:
Component:  Tor                   |        Version:
 Keywords:  tor-bridge tor-guard  |  Actual Points:
Parent ID:                        |         Points:
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 In `choose_random_entry_impl()` we have:

 {{{
 choose_and_finish:
   if (entry_list_is_constrained(options)) {
     /* We need to weight by bandwidth, because our bridges or entryguards
      * were not already selected proportional to their bandwidth. */
     node = node_sl_choose_by_bandwidth(live_entry_guards,
 WEIGHT_FOR_GUARD);
 }}}

 This means that bridges are also selected proportional to their bandwidth.
 However, since there is no bandwidth authorities for bridges their
 bandwidth is self-reported and potentially a lie. For this reason, it's
 probably not a good idea to use those values during path selection, since
 an evil bridge can try to dominate the guard probability.

 Fortunately, we also have `bridge_get_advertised_bandwidth_bounded()`
 which bounds bridges bandwidth between 20kB/s and 100kB/s. So the danger
 can't be that great.

 Still, it might be a better idea to pick amongst bridges in a uniform
 random way.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/12201>
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