[tor-dev] Weird interactions between TBB and Hidden Services upon HS kill/restart

[George Kadianakis]

Alec Muffett <alecm at fb.com> writes:

> For the sake of documentation I thought I would share this here:
>
> I have a (test) Hidden Service, running vanilla tor 0.2.6.10
>
> <snip>
>
> The TBB logfile contains the following sequence, pertinent to the second connection attempt:
>
>   ---- start ----
>   >Nov 12 17:46:27.000 [info] connection_ap_handshake_rewrite_and_attach(): Got a hidden service request for ID 'MY_ONION'
>   >Nov 12 17:46:27.000 [info] circuit_get_open_circ_or_launch(): Chose INTROPOINT_3 as intro point for 'MY_ONION'.
>   >Nov 12 17:46:27.000 [info] rend_client_introduction_acked(): Got nack for MY_ONION from INTROPOINT_3...
>   >Nov 12 17:46:27.000 [info] rend_client_report_intro_point_failure(): 2 options left for "MY_ONION".
>   >Nov 12 17:46:28.000 [info] rend_client_introduction_acked(): Got nack for MY_ONION from INTROPOINT_2...
>   >Nov 12 17:46:28.000 [info] rend_client_report_intro_point_failure(): 1 options left for "MY_ONION".
>   >Nov 12 17:46:28.000 [info] rend_client_introduction_acked(): Got nack for MY_ONION from INTROPOINT_1...
>   >Nov 12 17:46:28.000 [info] rend_client_report_intro_point_failure(): No more intro points remain for "MY_ONION". Re-fetching descriptor.
>
> Okay, this makes sense, all the IPs are invalid because I killed the daemon, none of them are reachable...
>
>   >Nov 12 17:46:28.000 [info] directory_get_from_hs_dir(): Sending fetch request
>   > for v2 descriptor for service 'MY_ONION' with descriptor ID 'MY_DESC_2',
>   > auth type 0, and descriptor cookie '[none]' to hidden service directory
>   > HSDIR_3
>
> Wait, is it relevant that it has picked descriptor ID 'MY_DESC_2' here, not the
> prior 'MY_DESC_1'?  The latter crops-up further down.  Perhaps this is a DHT
> thing?  This is the only reference to MY_DESC_2...
>

Maybe MY_DESC_2 is the descriptor ID of the second replica? There are two
replicas for an HS descriptor, each served by 3 HSDIrs.

The descriptor ID is formed like this:

         descriptor-id =
             H(permanent-id | H(time-period | descriptor-cookie | replica))

This might also explain why you get the "we already have this descriptor"
message below.

Not sure though, for more confidence I would have to look deeper here.

>   >Nov 12 17:46:29.000 [info] rend_cache_store_v2_desc_as_client(): Service descriptor with service ID MY_ONION, every intro points are unusable. Discarding it.
>
> That sounds okay, garbage collection of dead data is good...
>
>   >Nov 12 17:46:29.000 [info] directory_get_from_hs_dir(): Sending fetch request
>   > for v2 descriptor for service 'MY_ONION' with descriptor ID 'MY_DESC_1',
>   > auth type 0, and descriptor cookie '[none]' to hidden service directory
>   > HSDIR_4
>
> Wait, now we are re-fetching MY_DESC_1 again?...
>
>   >Nov 12 17:46:30.000 [info] rend_cache_store_v2_desc_as_client(): We already have this service descriptor MY_ONION.
>
> And it thinks we already have it? But didn't we just discard it?...
>
>   >Nov 12 17:46:30.000 [notice] Closing stream for 'MY_ONION.onion': hidden service is unavailable (try again later).
>
> And there is the connection failure, and it looks like it didn't find a new descriptor, or rejected a new one if it found it - assuming it found it at all...
>
>   >Nov 12 17:46:30.000 [info] rend_client_note_connection_attempt_ended(): Connection attempt for MY_ONION has ended; cleaning up temporary state.
>   >Nov 12 17:46:30.000 [info] rend_client_note_connection_attempt_ended(): Connection attempt for MY_ONION has ended; cleaning up temporary state.
>
> Try "reload" again, just for good luck:
>
>   >Nov 12 17:46:40.000 [info] connection_ap_handshake_rewrite_and_attach(): Got a hidden service request for ID 'MY_ONION'
>   >Nov 12 17:46:40.000 [info] connection_ap_handshake_rewrite_and_attach(): Unknown descriptor MY_ONION. Fetching.
>   >Nov 12 17:46:40.000 [info] directory_get_from_hs_dir(): Sending fetch request
>   > for v2 descriptor for service 'MY_ONION' with descriptor ID 'MY_DESC_1',
>   > auth type 0, and descriptor cookie '[none]' to hidden service directory
>   > HSDIR_2
>   >Nov 12 17:46:41.000 [info] rend_cache_store_v2_desc_as_client(): We already have this service descriptor MY_ONION.
>   >Nov 12 17:46:41.000 [notice] Closing stream for 'MY_ONION.onion': hidden service is unavailable (try again later).
>   >Nov 12 17:46:41.000 [info] rend_client_note_connection_attempt_ended(): Connection attempt for MY_ONION has ended; cleaning up temporary state.
>   >Nov 12 17:46:41.000 [info] rend_client_note_connection_attempt_ended(): Connection attempt for MY_ONION has ended; cleaning up temporary state.
>   ---- end ----
>
> So, it looks like one of three things:
>
> - perhaps TBB is not actually discarding the dead descriptor
> - or perhaps TBB is re-fetching the old descriptor and failing connections again
> - or perhaps TBB is fetching the new descriptor and rejecting it in favour of the old one, which it hasn't really discarded.
>
> In any case: killing TBB and restarting it seems to fix this situation, so it's something on the client side at fault?
>
>     - alec
>
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