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