[tor-bugs] #9546 [- Select a component]: Link handshake fails with "Received unexpected cell command 10" when clocks are skewed

[Tor Bug Tracker & Wiki]

#9546: Link handshake fails with "Received unexpected cell command 10" when clocks
are skewed
----------------------------------+-----------------------------------------
 Reporter:  zwol                  |          Owner:                  
     Type:  defect                |         Status:  new             
 Priority:  normal                |      Milestone:                  
Component:  - Select a component  |        Version:  Tor: 0.2.4.15-rc
 Keywords:                        |         Parent:                  
   Points:                        |   Actualpoints:                  
----------------------------------+-----------------------------------------
 If there is sufficient clock skew between a Tor client and its bridge, the
 client starts carrying out the link handshake protocol incorrectly,
 leading to (info-level) errors like this on the server side:

 {{{
 Aug 19 19:21:13.000 [info] channel_register(): Channel 0x7fcbd2927d00
 (global ID 14) in state opening (1) registered with no identity digest
 Aug 19 19:21:13.000 [info] channel_tls_process_versions_cell(): Negotiated
 version 4 with [scrubbed]:49733; Sending cells: VERSIONS CERTS NETINFO
 Aug 19 19:21:13.000 [info] channel_tls_process_certs_cell(): Got some good
 certificates from [scrubbed]:49733: Waiting for AUTHENTICATE.
 Aug 19 19:21:13.000 [info] channel_tls_handle_cell(): Received unexpected
 cell command 10 in chan state opening / conn state handshaking (Tor, v3
 handshake); closing the connection.
 }}}

 From IRC (edited):

 {{{
 <nickm> Looks like the client is sending a CREATE2 cell before the
 handshake is done.
 <nickm> It appears that the client isn't sending a NETINFO cell.
 <nickm> If this is an unmodified Tor client and server, then that's a bug.
 <zwol> 0.2.4.15-rc (git-f41c20b344fb7359) on the server.
 <zwol> 0.2.4.15-rc (git-e7b435872cce464f) on the client.
 <zwol> f41c20b344fb7359 corresponds to the tor 0.2.4.15-rc-1 package from
 current Debian unstable, and e7b435872cce464f is what was shipped with TBB
 3.0a3.
 }}}

 I will attach two client-side info-level logs: one demonstrating the
 problem, one successful connection.  The only configuration difference
 between the two is that in the problem case, the client's clock was 26
 hours fast:

 {{{
 Aug 21 18:57:01.000 [info] connection_dir_client_reached_eof(): Received
 directory with skewed time (server '[scrubbed]:9002'): It seems that our
 clock is ahead by 1 days, 2 hours, 32 minutes, or that theirs is behind.
 Tor requires an accurate clock to work: please check your time, timezone,
 and date settings.
 }}}

-- 
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/9546>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online