#24367: Changing pluggable transports (during start-up) in Tor Browser is broken -------------------------------------------------+------------------------- Reporter: gk | Owner: (none) Type: defect | Status: | needs_information Priority: Medium | Milestone: Tor: | 0.3.2.x-final Component: Core Tor/Tor | Version: Tor: | 0.3.0.1-alpha Severity: Normal | Resolution: Keywords: 030-backport, 031-backport, | Actual Points: regression, tor-bridge-client, s8-errors, | tbb-wants | Parent ID: | Points: 0.5 Reviewer: | Sponsor: | Sponsor8-can -------------------------------------------------+-------------------------
Comment (by gk): We debugged this a bit on IRC today and it turned out that a crucial part in this bug seems to be that one of the `obfs3` and one of the `obfs4` bridges share the same ID. So, if one chooses an `obfs3` bridge Tor Launcher issues a `SETCONF` command like {{{ [12-12 16:21:14] TorLauncher DBUG: Sending Tor command: SETCONF UseBridges=1 Bridge="obfs3 109.105.109.163:38980 1E05F577A0EC0213F971D81BF4D86A9E4E8229ED" Bridge="obfs3 109.105.109.163:47779 4C331FA9B3D1D6D8FB0D8FBBF0C259C360D97E6A" Bridge="obfs3 83.212.101.3:80 A09D536DD1752D542E1FBB3C9CE4449D51298239" Bridge="obfs3 169.229.59.75:46328 AF9F66B7B04F8FF6F32D455F05135250A16543C9" Bridge="obfs3 169.229.59.74:31493 AF9F66B7B04F8FF6F32D455F05135250A16543C9" }}} . When pressing `Cancel` during the bootstrap process and selecting the `obfs4` option instead, Tor Launcher is sending a similar `SETCONF` command. However, later on we easily get a bootstrap error like {{{ Dec 12 17:21:35.000 [warn] Problem bootstrapping. Stuck at 85%: Finishing handshake with first hop. (DONE; DONE; count 1; recommendation warn; host A09D536DD1752D542E1FBB3C9CE4449D51298239 at 83.212.101.3:80) }}} The ID A09D536DD1752D542E1FBB3C9CE4449D51298239 is used by one of the `obfs4` bridges as well (the IP is the same but the port is different (50002 in this case)). It seems things are working much better if I remove the `obfs3` bridge with A09D536DD1752D542E1FBB3C9CE4449D51298239 first before starting. I did some tests and I never ran into the bootstrap error. FWIW it is visible as well if one starts with `obfs4` first and switches to `obfs3`, although it seems the error does not pop up outright (as in the `obfs3` -> `obfs4` switch) but gets visible once I press `Cancel` in Tor Launcher after the bootstrap process is stuck. According to Nick the issue seems to be that Tor Browser will have a guard entry for the bridge it was using before but it seems the lookup which is done by fingerprint _and_ address is not working as expected. So, that's the error case in 4) in my comment:description. I am not sure about the stalling part yet. My current plan is to open a new ticket once all open issues related to that one are fixed/merged and I can still come up with a scenario to reproduce a stalled bootstrap process. -- Ticket URL: <https://trac.torproject.org/projects/tor/ticket/24367#comment:26> Tor Bug Tracker & Wiki <https://trac.torproject.org/> The Tor Project: anonymity online
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