Bug stracktrace when pluggable transport cannot bind to port
I have just setup some new obfs4 fast bridges running latest obfs4proxy from yawning / master (locally compiled on my server) and Tor 0.4.2.0-alpha-dev and encountered a bug stack trace when started to try with the pluggable transport listening on a port < 1024. This is well known, which is why even in the wiki page it is recommended and properly documented to use setcap in order to grant permission to the PT executable to bind to lower ports, but shouldn't it just warn and exit, instead of offering all this:
Jul 06 05:51:18.000 [warn] Server managed proxy encountered a method error. (obfs4 listen tcp <ipv4>:<port>: bind: permission denied)
Jul 06 05:51:18.000 [warn] Managed proxy at '/usr/local/bin/obfs4proxy' failed the configuration protocol and will be destroyed.
Jul 06 05:51:18.000 [err] tor_assertion_failed_(): Bug: ../src/feature/client/transports.c:1836: managed_proxy_stdout_callback: Assertion mp->conf_state == PT_PROTO_COMPLETED failed; aborting. (on Tor 0.4.2.0-alpha-dev )
Jul 06 05:51:18.000 [err] Bug: Assertion mp->conf_state == PT_PROTO_COMPLETED failed in managed_proxy_stdout_callback at ../src/feature/client/transports.c:1836: . Stack trace: (on Tor 0.4.2.0-alpha-dev )
Jul 06 05:51:18.000 [err] Bug: /usr/bin/tor(log_backtrace_impl+0x47) [0x559a576f5d87] (on Tor 0.4.2.0-alpha-dev )
Jul 06 05:51:18.000 [err] Bug: /usr/bin/tor(tor_assertion_failed_+0x147) [0x559a576f0ed7] (on Tor 0.4.2.0-alpha-dev )
Jul 06 05:51:18.000 [err] Bug: /usr/bin/tor(+0xd4a89) [0x559a575b8a89] (on Tor 0.4.2.0-alpha-dev )
Jul 06 05:51:18.000 [err] Bug: /usr/bin/tor(+0x1e4e4b) [0x559a576c8e4b] (on Tor 0.4.2.0-alpha-dev )
Jul 06 05:51:18.000 [err] Bug: /usr/lib/x86_64-linux-gnu/libevent-2.0.so.5(event_base_loop+0x6a0) [0x7f6f343265a0] (on Tor 0.4.2.0-alpha-dev )
Jul 06 05:51:18.000 [err] Bug: /usr/bin/tor(do_main_loop+0x105) [0x559a57555ed5] (on Tor 0.4.2.0-alpha-dev )
Jul 06 05:51:18.000 [err] Bug: /usr/bin/tor(tor_run_main+0x1245) [0x559a57543905] (on Tor 0.4.2.0-alpha-dev )
Jul 06 05:51:18.000 [err] Bug: /usr/bin/tor(tor_main+0x3a) [0x559a57540cfa] (on Tor 0.4.2.0-alpha-dev )
Jul 06 05:51:18.000 [err] Bug: /usr/bin/tor(main+0x19) [0x559a57540879] (on Tor 0.4.2.0-alpha-dev )
Jul 06 05:51:18.000 [err] Bug: /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf1) [0x7f6f32b7b2e1] (on Tor 0.4.2.0-alpha-dev )
Jul 06 05:51:18.000 [err] Bug: /usr/bin/tor(_start+0x2a) [0x559a575408ca] (on Tor 0.4.2.0-alpha-dev )What if it just stopped here:
Jul 06 05:51:18.000 [warn] Server managed proxy encountered a method error. (obfs4 listen tcp <ip>:<port>: bind: permission denied)
Jul 06 05:51:18.000 [warn] Managed proxy at '/usr/local/bin/obfs4proxy' failed the configuration protocol and will be destroyed.Or maybe even exit entirely so the operator can know something is really wrong.
Also, I don't know if this is related or not, I will try to make more tests to confirm or infirm this, but under Debian stable the bridges that are not run with setcap don't get a reasonable measured speed. Those with setcap that listen to lower ports have a bw of 2.5 - 3.5 MiB/s and those without setcap have a bw of 12 KiB/s - 70 KiB/s and they are all on the same infrastructure / hardware resources / internet speed. I will do some more digging to confirm this, right now 2 out of 2 obfs4 bridges that were configured without setcap did not get good bandwidth measurement even after 15 days of continuous uptime.