No Control Socket when DisableNetwork and User options are set

To successfully reproduce this, we need:

  1. set DisableNetwork to 1
  2. use User option as part of the Tor configuration
  3. run sudo Tor from a different user in a different group

Here are the specific steps to reproduce it. I tested it on Debian Stretch but it should be distribution independent:

user at host:~$ cat /home/user/my.torrc DataDirectory /tmp/tor ControlSocket /tmp/tor/control.sock ControlSocketsGroupWritable 1 CookieAuthentication 1 CookieAuthFileGroupReadable 1 CookieAuthFile /tmp/tor/control.authcookie SocksPort unix:/tmp/tor/socks.sock

user at host:~$ sudo /usr/bin/install -Z
-m 02755 -o debian-tor
-g debian-tor -d /tmp/tor

user at host:~$ ls -ld /tmp/tor/; ls -l /tmp/tor/ drwxr-s--- 2 debian-tor debian-tor 40 Feb 3 18:19 /tmp/tor/ total 0

user at host:~$ sudo /usr/bin/tor
-f /home/user/my.torrc
--User debian-tor
--DisableNetwork 1

There should be control.sock, but not:

user at host:~$ ls -ld /tmp/tor/; sudo ls -l /tmp/tor/ drwx--S--- 2 debian-tor debian-tor 100 Feb 3 20:00 /tmp/tor/ total 8 -rw-r----- 1 debian-tor debian-tor 32 Feb 3 20:00 control.authcookie -rw------- 1 debian-tor debian-tor 0 Feb 3 20:00 lock -rw------- 1 debian-tor debian-tor 215 Feb 3 20:00 state

To let Tor really open the control.sock, we need to reload Tor (yes, even though we just start it):

user at host:~$ ps -A | grep tor 863 ? 00:00:00 xenstore-watch 927 ? 00:00:04 tor-controlport 11851 pts/0 00:00:00 tor

user at host:~$ sudo /bin/kill -HUP 11851

user at host:~$ ls -ld /tmp/tor/; sudo ls -l /tmp/tor/ drwx--S--- 2 debian-tor debian-tor 120 Feb 3 20:01 /tmp/tor/ total 8 -rw-r----- 1 debian-tor debian-tor 32 Feb 3 20:01 control.authcookie srw-rw---- 1 debian-tor debian-tor 0 Feb 3 20:01 control.sock -rw------- 1 debian-tor debian-tor 0 Feb 3 20:01 lock -rw------- 1 debian-tor debian-tor 215 Feb 3 20:01 state

I guess the reason Yawning was not able to reproduce it is because User option was not set:

user at host:~$ sudo -u debian-tor
/usr/bin/tor -f /home/user/my.torrc
--DisableNetwork 1

[notice] Opening Control listener on /tmp/tor/control.sock

I was thinking Tor fixing /tmp/tor/ to 2700 may be the reason, but then I cannot explain why this will work with /tmp/tor/ set to 2700:

user at host:~$ sudo /usr/bin/tor
-f /home/user/my.torrc
--User debian-tor
--DisableNetwork 0

[notice] Opening Control listener on /tmp/tor/control.sock