[Bug 1986521] Re: ssh client spins if output fd closed

[Sergio Durigan Junior]

Thanks for taking the time to report the bug and make Ubuntu better.

I can reproduce the bug using your testcase, but that requires a VM with
a graphical environment installed.  Another way to reproduce the bug is
(from the upstream bug report):

$ lxc launch ubuntu-daily:jammy ssh-cpu
$ lxc shell ssh-cpu
# ssh HOST 2> >({exec 1>&2})

You can shell into the container from another terminal and use "htop" to
verify that ssh is using 100% of one of the CPU cores.

This seems to have been fixed upstream by the following commit:

https://github.com/openssh/openssh-
portable/commit/d6556de1db0822c76ba2745cf5c097d9472adf7c

I confirmed that this only happens on Jammy.  Focal and Kinetic are not
affected.

** Also affects: openssh (Ubuntu Jammy)
   Importance: Undecided
       Status: New

** Changed in: openssh (Ubuntu)
       Status: New => Fix Released

** Changed in: openssh (Ubuntu Jammy)
       Status: New => Triaged

** Changed in: openssh (Ubuntu Jammy)
   Importance: Undecided => Medium

** Bug watch added: OpenSSH Portable Bugzilla #3405
   https://bugzilla.mindrot.org/show_bug.cgi?id=3405

** Also affects: openssh via
   https://bugzilla.mindrot.org/show_bug.cgi?id=3405
   Importance: Unknown
       Status: Unknown

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https://bugs.launchpad.net/bugs/1986521

Title:
  ssh client spins if output fd closed

Status in portable OpenSSH:
  Unknown
Status in openssh package in Ubuntu:
  Fix Released
Status in openssh source package in Jammy:
  Triaged

Bug description:
  The OpenSSH package 8.9p1 as shipped with U22.04 (8.9p1-3) suffers from the bug described at
  https://bugzilla.mindrot.org/show_bug.cgi?id=3411 and https://bugzilla.mindrot.org/show_bug.cgi?id=3405

  A command such as "xterm -e 'ssh -f remote.host sleep 60'" will pop up
  an xterm, ask for whatever authentication is needed, close the xterm,
  and leave the ssh client spinning consuming CPU time for 60 seconds
  before it exits. It should leave the ssh client idle for 60 seconds.
  Many uses of ssh to launch graphical applications will be caught by
  this bug.

  This is fixed in OpenSSH 9.0p1 as the first bugfix listed in its
  release notes at https://www.openssh.com/txt/release-9.0

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