[Bug 1306877] Re: sshd stops accepting new connections after configuration reload

[Robie Basak]

Thank you for taking the time to report this bug and helping to make
Ubuntu better.

Setting Importance to Critical as this is an expected harmless operation
that will render the system essentially unreachable (and thus unusable)
for remote users (eg. just about all server users).

It seems to me that the STOP patch should only activate on first run,
not on a re-exec. I'll take a look.

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https://bugs.launchpad.net/bugs/1306877

Title:
  sshd stops accepting new connections after configuration reload

Status in “openssh” package in Ubuntu:
  Triaged

Bug description:
  When upstart is enabled, sshd stops accepting new connections after
  reloading configuration by "initctl reload ssh".

  It looks like sshd is frozen with SIGSTOP after receiving SIGHUP.

  [nya at sora ~]% ps auxww | grep sshd
  root     10557  0.0  0.1  61364  3056 ?        Ss   13:46   0:00 /usr/sbin/sshd -D
  [nya at sora ~]% sudo strace -p 10557
  Process 10557 attached
  select(7, [3 4], NULL, NULL, NULL^CProcess 10557 detached
   <detached ...>
  [nya at sora ~]% sudo reload ssh
  [nya at sora ~]% sudo strace -p 10557
  Process 10557 attached
  --- stopped by SIGSTOP ---

  I guess it's caused by a Debian-specific patch:
  debian/patches/sigstop.patch. The patch makes sshd STOP when it's
  ready to start and have upstart resume it by specifying "expect stop"
  in /etc/init/ssh.conf. On receiving SIGHUP sshd re-executes itself and
  STOPs again, but upstart does not perform resume.

  Reproduced under Ubuntu 14.04 Trusty
  Package version: openssh 1:6.6p1-2

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