[tor-bugs] #9904 [Tor]: When starting a Tor Relay, Tor may use a disabled network adapter for IP information

["Tor Bug Tracker & Wiki" <blackhole@xxxxxxxxxxxxxx>]

#9904: When starting a Tor Relay, Tor may use a disabled network adapter for IP
information
------------------------+-------------------------------
 Reporter:  hantwister  |          Owner:
     Type:  defect      |         Status:  new
 Priority:  minor       |      Milestone:
Component:  Tor         |        Version:  Tor: 0.2.3.25
 Keywords:              |  Actual Points:
Parent ID:              |         Points:
------------------------+-------------------------------
 I'm running OS X 10.8.5 on a Late 2008 13-inch AluminumÂMacBook. The
 computer has a private IP address on an ethernet adapter. When attempting
 to start a relay using the latest version of the Tor Browser Bundle
 (Vidalia 0.2.21, Tor 0.2.3.25 git-17c24b3118224d65), the following was
 continuously observed:

 {{{
 Oct 05 14:46:01.485 [Info] resolve_my_address(): Learned IP address
 '25.2.x.x' for local interface. Using that.

 Oct 05 14:46:01.486 [Debug] resolve_my_address(): Resolved Address to
 '25.2.x.x'.

 Oct 05 14:46:01.488 [Info] router_pick_published_address(): Success: chose
 address '25.2.x.x'.
 }}}
 When running ifconfig, the following was observed:

 {{{
 lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384
         options=3<RXCSUM,TXCSUM>
         inet6 fe80::1%lo0 prefixlen 64 scopeid 0x1
         inet 127.0.0.1 netmask 0xff000000
         inet6 ::1 prefixlen 128
 gif0: flags=8010<POINTOPOINT,MULTICAST> mtu 1280
 stf0: flags=0<> mtu 1280
 en0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
         options=27<RXCSUM,TXCSUM,VLAN_MTU,TSO4>
         ether 00:23:32:x:x:x
         media: autoselect
         status: inactive
 en1: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
         ether 00:23:12:x:x:x
         inet6 fe80::x:x:x:x%en1 prefixlen 64 scopeid 0x5
         inet 192.168.x.x netmask 0xffffff00 broadcast 192.168.x.255
         media: autoselect
         status: active
 p2p0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 2304
         ether 02:23:12:x:x:x
         media: autoselect
         status: inactive
 ham0: flags=8842<BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1404
         ether 7a:79:19:x:x:x
         inet 25.2.x.x netmask 0xff000000 broadcast 25.255.255.255
         inet6 fe80::x:x:x:x%ham0 prefixlen 64 scopeid 0x7
         inet6 2620:9b::x:x prefixlen 96
         open (pid 88)
 }}}
 Based on the source code ofÂget_interface_address6, it appears that Tor
 first looks for an interface with an IP address that is not a loopback, is
 not a multicast and is not an internal address. Because the connected
 ethernet adapter has an internal address, Tor skips over it, and the
 checks appear to succeed for the ham0 device. The ham0 device is actually
 a virtual device provided byÂLogMeInÂHamachi.

 In an attempt to remedy this, I stopped and quit Hamachi, and then used
 ifconfig to take the virtual network adapter down. In spite of this, Tor
 continued to produce log messages similar to those listed above, and
 continued to try to use the IP of the disabled virtual network adapter.

 Reviewing the source code forÂget_interface_addresses_raw, it appears that
 Tor only checks if a device's network family is IPv4 or IPv6. Adding a
 check to verify that the interface is up and running appears to fix the
 problem for me (patch attached), but I imagine such a change should be
 tested on a variety of *nix boxes.

-- 
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/9904>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online
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