[tor-bugs] #25882 [Core Tor/Tor]: clients not detecting stale onion service introduction points

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#25882: clients not detecting stale onion service introduction points
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 Reporter:  cypherpunks   |          Owner:  (none)
     Type:  defect        |         Status:  assigned
 Priority:  Medium        |      Milestone:  Tor: 0.3.4.x-final
Component:  Core Tor/Tor  |        Version:
 Severity:  Normal        |     Resolution:
 Keywords:  tor-hs        |  Actual Points:
Parent ID:  #22455        |         Points:
 Reviewer:                |        Sponsor:
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Comment (by asn):

 Thanks for all the information here. Really useful and there is indeed
 nasty bugs hiding here!

 IMO, there is a service-side bug that is causing this issue. Namely, for
 some reason, the HS has an introduction circuit open, which it ignores and
 does not reply to rendezvous requests coming from it. At the same time it
 seems like the HS has closed all its other intro circs and rotated
 descriptor. This might be related to #16702 or not.

 There is also a client-side issue, which is that the client continuously
 keeps on trying an introduction point which clearly does not work. The tor
 client should be smarter in this case and realize this and re-fetch the
 descriptor, but we should be smart here so that we don't cause needless HS
 desc fetches just because of broken rendezvous points or introduction
 points.

 IMO, we should first address the service-side issue which seems to be the
 root issue here and then address the client-side issue.

 To debug the service-side issue, we should try to reproduce it by setting
 up an HS and make it rotate descriptors and expire intro points quicker
 than usual (see `remove_invalid_intro_points()`), and then try connecting
 to it to see whether we can cause this behavior. FWIW, there is a whole
 mechanism in `rendservice.c` about expired intro points where we keep the
 intro circs open for a while, which I imagine is the root cause of this
 issue (see `expiring_nodes`).

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/25882#comment:15>
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