Bug#762633: openssh-server: -N option does behave on slave sessions (runs shell when it shouldn't)

[Oskar Liljeblad <oskar@osk.mine.nu>]

Package: openssh-server
Version: 1:6.6p1-7
Severity: normal

Hello

The -N option is documented as 'Do not execute a remote command'. This works
fine but when you run it on an existing master connection (i.e. as slave),
it will actually execute a shell.

To reproduce:

ssh -F /dev/null -o ControlMaster=auto -o ControlPath=socket -f -N localhost
ssh -F /dev/null -o ControlMaster=auto -o ControlPath=socket -N localhost

The first command works as expected, but the second will launch a shell
without prompt in the foreground (try 'ls /' to verify).  The same issue
occurs if you run '-f -N' both times (i.e.  first command above twice) - it
start a shell and you will see output from the shell such as "uname -a"
before ssh goes into background.

The -N command should not execute a shell. If the master connection exists
already, it should instead behave as '-O forward' ("request forwardings
without command execution") which works correctly.

Regards,

Oskar Liljeblad

-- System Information:
Debian Release: jessie/sid
  APT prefers testing
  APT policy: (990, 'testing'), (500, 'testing-updates'), (500, 'unstable')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 3.14-2-amd64 (SMP w/8 CPU cores)
Locale: LANG=POSIX, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash

Versions of packages openssh-server depends on:
ii  adduser                3.113+nmu3
ii  debconf [debconf-2.0]  1.5.53
ii  dpkg                   1.17.13
ii  init-system-helpers    1.21
ii  libc6                  2.19-11
ii  libcomerr2             1.42.12-1
ii  libgssapi-krb5-2       1.12.1+dfsg-9
ii  libkrb5-3              1.12.1+dfsg-9
ii  libpam-modules         1.1.8-3.1
ii  libpam-runtime         1.1.8-3.1
ii  libpam0g               1.1.8-3.1
ii  libselinux1            2.3-2
ii  libssl1.0.0            1.0.1i-2
ii  libwrap0               7.6.q-25
ii  lsb-base               4.1+Debian13
ii  openssh-client         1:6.6p1-7
ii  openssh-sftp-server    1:6.6p1-7
ii  procps                 1:3.3.9-7
ii  zlib1g                 1:1.2.8.dfsg-2

Versions of packages openssh-server recommends:
ii  ncurses-term  5.9+20140712-2
ii  xauth         1:1.0.9-1

Versions of packages openssh-server suggests:
pn  molly-guard   <none>
pn  monkeysphere  <none>
pn  rssh          <none>
pn  ssh-askpass   <none>
pn  ufw           <none>

-- Configuration Files:
/etc/pam.d/sshd changed [not included]

-- debconf information excluded