[Bug 1213743] Re: subshell that instantly locks up bash, dash, ksh, tcsh, and zsh

[Thorsten Glaser]

Not a bug. User stupidity. Unix gives you the rope to hang yourself.

There are several different strategies to recover from this, among
others:

- start another terminal, kill the yes process

- exit the shell

It's creating a detached background process. *Of course* you won’t be
able to use normal job handling on it.

Additionally, your diagnosis is all wrong: The shell does not become
totally unresponsive. In fact, it’s usable just fine, except your
terminal is too slow to keep up with the I/O flood from yes (naturally).

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https://bugs.launchpad.net/bugs/1213743

Title:
  subshell that instantly locks up bash, dash, ksh, tcsh, and zsh

Status in “bash” package in Ubuntu:
  New
Status in “dash” package in Ubuntu:
  New
Status in “ksh” package in Ubuntu:
  New
Status in “tcsh” package in Ubuntu:
  New
Status in “zsh” package in Ubuntu:
  New

Bug description:
  Type this at a shell prompt in gnome-terminal:

  $ (yes&)
  y
  y
  y
  y
  y
  y
  ...

  Denial of service. Shell becomes totally unresponsive. Subshell
  command is uninterruptible.

  An old one that affects bash, dash, ksh, tcsh, and zsh shells at least
  in all versions in Ubuntu and further back in Ubuntu pre-history too.

  Please note the issue is not related to
  https://wiki.ubuntu.com/SecurityTeam/Policies#Unlimited_Local_Resource_Utilization

   $ (yes &)
  is not a fork bomb or any other kind of resource overutilization. There is only one subshell and only one subprocess being executed in it.

  The issue is with buggy signal handling.

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