openssh unix dev - Oct 2011 - OpenSSH hanging

Hi there,
   I'm having some strange behaviour from OpenSSH
   It presents itself when using the "ssh -t" / pseudo terminal.
   We are using this feature to update the wtmp and it is working fine on
   SuSE and RH, but our AIX hosts are getting hung. The first attempt is
   usually successful, but eventually, the session is hung and the CRTL-Z
   does not put the process into background.
   The ssh -v output
   OpenSSH_5.4p1, OpenSSL 0.9.8m 25 Feb 2010
   and when I run a truss:
   [snipped]
   kwrite(4, " ?9E ? d ? ? e 9 ? O\b ?".., 576)    = 576
   _select(5, 0x2005DC28, 0x00000000, 0x00000000, 0x00000000) = 1
   kread(4, " ?8E07 y ? ? ? } ? < ? ?".., 8192)    = 32
   kfcntl(0, F_DUPFD, 0x00000000)                  = 5
   kfcntl(1, F_DUPFD, 0x00000000)                  = 6
   kfcntl(2, F_DUPFD, 0x00000000)                  = 7
   kioctl(5, 22528, 0x00000000, 0x00000000)        = 0
   kioctl(6, 22528, 0x00000000, 0x00000000)        = 0
   kioctl(7, 22528, 0x00000000, 0x00000000)        = 0
   kfcntl(5, F_SETFD, 0x00000001)                  = 0
   kfcntl(6, F_SETFD, 0x00000001)                  = 0
   kfcntl(7, F_SETFD, 0x00000001)                  = 0
   kioctl(6, 22528, 0x00000000, 0x00000000)        = 0
   sigprocmask(2, 0xF0277960, 0x2FF21AB0)          = 0
   _sigaction(1, 0x00000000, 0x2FF21B60)           = 0
   thread_setmymask_fast(0x00000000, 0x00000000, 0x00000000, 0x11FA00A9,
   0x00000000, 0x00000013, 0x00000000, 0x00000000) = 0x00000000
   sigprocmask(2, 0xF0277960, 0x2FF21AB0)          = 0
   _sigaction(1, 0x2FF21B50, 0x00000000)           = 0
   thread_setmymask_fast(0x00000000, 0x00000000, 0x00000000, 0x11FA00A9,
   0x00000000, 0x00000014, 0x00000000, 0x00000000) = 0x00000000
   sigprocmask(2, 0xF0277960, 0x2FF21AB0)          = 0
   _sigaction(1, 0x00000000, 0x2FF21B60)           = 0
   thread_setmymask_fast(0x00000000, 0x00000000, 0x00000000, 0x11FA00A9,
   0x00000000, 0x00000016, 0x00000000, 0x00000000) = 0x00000000
   sigprocmask(2, 0xF0277960, 0x2FF21AB0)          = 0
   _sigaction(1, 0x2FF21B50, 0x00000000)           = 0
   thread_setmymask_fast(0x00000000, 0x00000000, 0x00000000, 0x11FA00A9,
   0x00000000, 0x00000018, 0x00000000, 0x00000000) = 0x00000000
   sigprocmask(2, 0xF0277960, 0x2FF21AB0)          = 0
   _sigaction(2, 0x00000000, 0x2FF21B60)           = 0
   thread_setmymask_fast(0x00000000, 0x00000000, 0x00000000, 0x11FA00A9,
   0x00000000, 0x00000013, 0x00000000, 0x00000000) = 0x00000000
   sigprocmask(2, 0xF0277960, 0x2FF21AB0)          = 0
   _sigaction(2, 0x2FF21B50, 0x00000000)           = 0
   thread_setmymask_fast(0x00000000, 0x00000000, 0x00000000, 0x11FA00A9,
   0x00000000, 0x00000016, 0x00000000, 0x00000000) = 0x00000000
   sigprocmask(2, 0xF0277960, 0x2FF21AB0)          = 0
   _sigaction(2, 0x00000000, 0x2FF21B60)           = 0
   thread_setmymask_fast(0x00000000, 0x00000000, 0x00000000, 0x11FA00A9,
   0x00000000, 0x00000016, 0x00000000, 0x00000000) = 0x00000000
   sigprocmask(2, 0xF0277960, 0x2FF21AB0)          = 0
   _sigaction(2, 0x2FF21B50, 0x00000000)           = 0
   thread_setmymask_fast(0x00000000, 0x00000000, 0x00000000, 0x11FA00A9,
   0x00000000, 0x00000016, 0x00000000, 0x00000000) = 0x00000000
   sigprocmask(2, 0xF0277960, 0x2FF21AB0)          = 0
   _sigaction(3, 0x00000000, 0x2FF21B60)           = 0
   thread_setmymask_fast(0x00000000, 0x00000000, 0x00000000, 0x11FA00A9,
   0x00000000, 0x00000014, 0x00000000, 0x00000000) = 0x00000000
   sigprocmask(2, 0xF0277960, 0x2FF21AB0)          = 0
   _sigaction(3, 0x2FF21B50, 0x00000000)           = 0
   thread_setmymask_fast(0x00000000, 0x00000000, 0x00000000, 0x11FA00A9,
   0x00000000, 0x0000001B, 0x00000000, 0x00000000) = 0x00000000
   sigprocmask(2, 0xF0277960, 0x2FF21AB0)          = 0
   _sigaction(3, 0x00000000, 0x2FF21B60)           = 0
   thread_setmymask_fast(0x00000000, 0x00000000, 0x00000000, 0x11FA00A9,
   0x00000000, 0x00000013, 0x00000000, 0x00000000) = 0x00000000
   sigprocmask(2, 0xF0277960, 0x2FF21AB0)          = 0
   _sigaction(3, 0x2FF21B50, 0x00000000)           = 0
   thread_setmymask_fast(0x00000000, 0x00000000, 0x00000000, 0x11FA00A9,
   0x00000000, 0x00000016, 0x00000000, 0x00000000) = 0x00000000
   sigprocmask(2, 0xF0277960, 0x2FF21AB0)          = 0
   _sigaction(15, 0x00000000, 0x2FF21B60)          = 0
   thread_setmymask_fast(0x00000000, 0x00000000, 0x00000000, 0x11FA00A9,
   0x00000000, 0x00000015, 0x00000000, 0x00000000) = 0x00000000
   sigprocmask(2, 0xF0277960, 0x2FF21AB0)          = 0
   _sigaction(15, 0x2FF21B50, 0x00000000)          = 0
   thread_setmymask_fast(0x00000000, 0x00000000, 0x00000000, 0x11FA00A9,
   0x00000000, 0x00000015, 0x00000000, 0x00000000) = 0x00000000
   sigprocmask(2, 0xF0277960, 0x2FF21AB0)          = 0
   _sigaction(15, 0x00000000, 0x2FF21B60)          = 0
   thread_setmymask_fast(0x00000000, 0x00000000, 0x00000000, 0x11FA00A9,
   0x00000000, 0x00000019, 0x00000000, 0x00000000) = 0x00000000
   sigprocmask(2, 0xF0277960, 0x2FF21AB0)          = 0
   _sigaction(15, 0x2FF21B50, 0x00000000)          = 0
   thread_setmymask_fast(0x00000000, 0x00000000, 0x00000000, 0x11FA00A9,
   0x00000000, 0x0000001A, 0x00000000, 0x00000000) = 0x00000000
   sigprocmask(2, 0xF0277960, 0x2FF21AB0)          = 0
   _sigaction(28, 0x00000000, 0x2FF21B60)          = 0
   thread_setmymask_fast(0x00000000, 0x00000000, 0x00000000, 0x11FA00A9,
   0x00000000, 0x0000001E, 0x00000000, 0x00000000) = 0x00000000
   sigprocmask(2, 0xF0277960, 0x2FF21AB0)          = 0
   _sigaction(28, 0x2FF21B50, 0x00000000)          = 0
   thread_setmymask_fast(0x00000000, 0x00000000, 0x00000000, 0x11FA00A9,
   0x00000000, 0x0000001B, 0x00000000, 0x00000000) = 0x00000000
   kioctl(0, 22528, 0x00000000, 0x00000000)        = 0
   kioctl(0, 21505, 0x2FF21B50, 0x00000000)        = 0
   kioctl(0, 22528, 0x00000000, 0x00000000)        = 0
   kioctl(0, 21507, 0x2FF21B50, 0x00000000)        = 0
                                                      _select(8,
   0x2005DC28, 0x2005EBB8, 0x00000000, 0x00000000) = 1

                                            kwrite(4, " ? ? >9A06 ?
   0 L 319 ?92".., 128)        = 128
                        _select(8, 0x2005DC28, 0x2005EBB8, 0x00000000,
   0x00000000) = 1

              kread(4, " ? ? c ? g :1D1B ?11 ? 9".., 8192)
    = 48

                                                               kioctl(0,
   1074295912, 0x2FF21A04, 0x00000000)        = 0
                                              getsockopt(4, 6, 1,
   0x2FF219D0, 0x2FF219D4)        = 0

                      setsockopt(4, 6, 1, 0x2FF219D0, 4)                   0


   ngetsockname(4, 0x2FF21480, 0x2FF21988)                = 0
                                                      setsockopt(4, 0, 3,
   0x2FF219D0, 4)                = 0

                              _select(8, 0x2005DC28, 0x2005EBB8,
   0x00000000, 0x00000000) = 1
                     kwrite(4, "96 C C F v ? Q   l ? ?\f".., 384)
        = 384

   _select(8, 0x2005DC28, 0x2005EBB8, 0x00000000, 0x00000000)
   (sleeping...)
   Henry Barber
   Australian Development Lab
   office: +61 7 5552 4050
   mobile: +61 449 101 452

On 7/10/11 9:58 AM, Henry Barber wrote:
>     I'm having some strange behaviour from OpenSSH
>     It presents itself when using the "ssh -t" / pseudo terminal.
>     We are using this feature to update the wtmp and it is working fine on
>     SuSE and RH, but our AIX hosts are getting hung. The first attempt is
>     usually successful, but eventually, the session is hung and the CRTL-Z
>     does not put the process into background.
>     The ssh -v output
>     OpenSSH_5.4p1, OpenSSL 0.9.8m 25 Feb 2010
This could happen with old versions of OpenSSH: they did not correctly 
handle the case where pty allocation failed.

This was fixed in 5.6.  From http://www.openssh.com/txt/release-5.6:

  Kill channel when pty allocation requests fail. Fixed stuck client
    if the server refuses pty allocation (bz#1698)

-- 
Darren Tucker (dtucker at zip.com.au)
GPG key 8FF4FA69 / D9A3 86E9 7EEE AF4B B2D4  37C9 C982 80C7 8FF4 FA69
     Good judgement comes with experience. Unfortunately, the experience
usually comes from bad judgement.