ssh -g has no effect if master socket already open

[Ken Sharp]

From the man page:
 -g Allows remote hosts to connect to local forwarded ports.

When working with a control socket, this works fine if -g is included with the initial connect attempt, for example:

$ cat ~/.ssh/config
Host *
ControlMaster auto
ControlPath ~/.ssh/%r@%h:%p

$ ssh -gTfNL 12345:localhost:12345 host
$ netstat -tln

tcp 0 0 0.0.0.0:12345 0.0.0.0:* LISTEN -

$ lsof -n

ssh 182446 user 3u IPv4 76397177 0t0 TCP 192.168.0.9:51181->192.168.0.15:ssh (ESTABLISHED)
ssh 182446 user 4u IPv4 76397181 0t0 TCP *:3128 (LISTEN)
ssh 182446 user 5u IPv6 76397182 0t0 TCP *:3128 (LISTEN)

and similarly:

$ ssh -g host
user@host:~$ exit
$ ssh -gTfNL 12345:localhost:12345 host
$ netstat -tln

tcp 0 0 0.0.0.0:12345 0.0.0.0:* LISTEN -

However, if it isn't then -g is ignored on subsequent attempts to forward ports:

$ ssh host
user@host:~$ exit
$ ssh -g -L 12345:localhost:12345 host
$ netstat -tln

tcp 0 0 127.0.0.1:12345 0.0.0.0:* LISTEN -

$ lsof -n

ssh 182399 user 3u IPv4 76390396 0t0 TCP 192.168.0.9:51178->192.168.0.15:ssh (ESTABLISHED)
ssh 182399 user 4u unix 0x0000000000000000 0t0 76390976 /home/user/.ssh/user@host
ssh 182399 user 6u IPv6 76392394 0t0 TCP [::1]:3128 (LISTEN)
ssh 182399 user 7u IPv4 76392395 0t0 TCP 127.0.0.1:3128 (LISTEN)

This doesn't really make sense: ssh should still be capable of binding to the correct address as requested.

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: ssh (not installed)
ProcVersionSignature: Ubuntu 3.8.0-33.48~precise1-generic 3.8.13.11
Uname: Linux 3.8.0-33-generic i686
ApportVersion: 2.0.1-0ubuntu17.6
Architecture: i386
Date: Tue Dec 10 12:59:33 2013
InstallationMedia: Ubuntu-Server 12.04.1 LTS "Precise Pangolin" - Release i386 (20120817.3)
MarkForUpload: True
ProcEnviron:
 LANGUAGE=en_GB:en
 TERM=xterm
 PATH=(custom, no user)
 LANG=en_GB.UTF-8
 SHELL=/bin/bash
SourcePackage: openssh
UpgradeStatus: No upgrade log present (probably fresh install)

[Ken Sharp (kennybobs)]

Same in Trusty and Debian Testing.

[Imwellcushtymelike (imwellcushtymelike)]

From the man page:
 -g Allows remote hosts to connect to local forwarded ports.

When working with a control socket, this works fine if -g is included with the initial connect attempt, for example:

$ cat ~/.ssh/config
Host *
ControlMaster auto
ControlPath ~/.ssh/%r@%h:%p

$ ssh -gTfNL 12345:localhost:12345 host
$ netstat -tln

tcp 0 0 0.0.0.0:12345 0.0.0.0:* LISTEN -

$ lsof -n

ssh 182446 user 3u IPv4 76397177 0t0 TCP 192.168.0.9:51181->192.168.0.15:ssh (ESTABLISHED)
ssh 182446 user 4u IPv4 76397181 0t0 TCP *:3128 (LISTEN)
ssh 182446 user 5u IPv6 76397182 0t0 TCP *:3128 (LISTEN)

and similarly:

$ ssh -g host
user@host:~$ exit
$ ssh -gTfNL 12345:localhost:12345 host
$ netstat -tln

tcp 0 0 0.0.0.0:12345 0.0.0.0:* LISTEN -

However, if it isn't then -g is ignored on subsequent attempts to forward ports:

$ ssh host
user@host:~$ exit
$ ssh -g -L 12345:localhost:12345 host
$ netstat -tln

tcp 0 0 127.0.0.1:12345 0.0.0.0:* LISTEN -

$ lsof -n

ssh 182399 user 3u IPv4 76390396 0t0 TCP 192.168.0.9:51178->192.168.0.15:ssh (ESTABLISHED)
ssh 182399 user 4u unix 0x0000000000000000 0t0 76390976 /home/user/.ssh/user@host
ssh 182399 user 6u IPv6 76392394 0t0 TCP [::1]:3128 (LISTEN)
ssh 182399 user 7u IPv4 76392395 0t0 TCP 127.0.0.1:3128 (LISTEN)

This doesn't really make sense: ssh should still be capable of binding to the correct address as requested.

From:
https://bugs.launchpad.net/debian/+source/openssh/+bug/1259939
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=731950