[tor-bugs] #21771 [Core Tor/Tor]: Cannot change bridge (with Tor 0.3.0.4-rc)

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#21771: Cannot change bridge (with Tor 0.3.0.4-rc)
---------------------------------+------------------------------------
 Reporter:  torvlnt33r           |          Owner:  asn
     Type:  defect               |         Status:  assigned
 Priority:  Very High            |      Milestone:  Tor: 0.3.1.x-final
Component:  Core Tor/Tor         |        Version:  Tor: 0.3.0.4-rc
 Severity:  Normal               |     Resolution:
 Keywords:  bridge 030-backport  |  Actual Points:
Parent ID:                       |         Points:  1
 Reviewer:                       |        Sponsor:
---------------------------------+------------------------------------

Comment (by asn):

 With Nick we discussed that the right fix is probably to implement the
 original intention of the code snippet here:
 {{{
 get_max_sample_size(guard_selection_t *gs,
                     int n_guards)
 {
 ...
   /* With bridges, max_sample is "all of them" */
   if (using_bridges)
     return n_guards;
 }}}

 and actually make the max_sample size be "all of them" in the bridge case
 instead of just being the number of bridges in torrc.

 Possible implementations:

 a) The obvious (but slightly dirty) way of doing this would be to change
 `return n_guards` above to `return INT_MAX`. I verified that this would
 fix the bug of this ticket.

 b) If we want a nicer semantic than `INT_MAX` we could perhaps return the
 number of bridges in our torrc ''plus'' the number of currently sampled
 bridges.

 c) The third alternative would be to return `DFLT_MAX_SAMPLE_SIZE` but
 that would not actually fix all edge cases, since if our sampled guard
 list contains lots of old bridges we could actually hit the limit.

 Personally, I think going with (a) and a small comment describing the
 logic is fine. Alternatively, we could go with (b) if we want to seem
 smarter.

 I can write a quick patch here after we decide on the approach.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/21771#comment:7>
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