[Bug 1683923] [NEW] Empty extglob patterns hang bash

[John Valko]

Public bug reported:

Bash hangs when extglobs with no patterns are specified.

Example:

$ echo !()

should print the contents of the current directory, but actually makes
bash hang with 100% CPU usage. Also affects other pattern types, e.g.
@() and ?(). Non-empty patterns work correctly.

After executing a command containing such a glob, a SIGKILL is required
to terminate the process.

Additional info:

$ lsb_release  -rd
Description:	Ubuntu 14.04.4 LTS
Release:	14.04

$ apt-cache policy bash
bash:
  Installed: 4.3-7ubuntu1.5
  Candidate: 4.3-7ubuntu1.5
  Version table:
 *** 4.3-7ubuntu1.5 0
        500 http://mirrors.linode.com/ubuntu/ trusty-updates/main amd64 Packages
        500 http://mirrors.linode.com/ubuntu/ trusty-security/main amd64 Packages
                                                                                        100 /var/lib/dpkg/status
     4.3-6ubuntu1 0
        500 http://mirrors.linode.com/ubuntu/ trusty/main amd64 Packages

** Affects: bash (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1683923

Title:
  Empty extglob patterns hang bash

Status in bash package in Ubuntu:
  New

Bug description:
  Bash hangs when extglobs with no patterns are specified.

  Example:

  $ echo !()

  should print the contents of the current directory, but actually makes
  bash hang with 100% CPU usage. Also affects other pattern types, e.g.
  @() and ?(). Non-empty patterns work correctly.

  After executing a command containing such a glob, a SIGKILL is
  required to terminate the process.

  Additional info:

  $ lsb_release  -rd
  Description:	Ubuntu 14.04.4 LTS
  Release:	14.04

  $ apt-cache policy bash
  bash:
    Installed: 4.3-7ubuntu1.5
    Candidate: 4.3-7ubuntu1.5
    Version table:
   *** 4.3-7ubuntu1.5 0
          500 http://mirrors.linode.com/ubuntu/ trusty-updates/main amd64 Packages
          500 http://mirrors.linode.com/ubuntu/ trusty-security/main amd64 Packages
                                                                                          100 /var/lib/dpkg/status
       4.3-6ubuntu1 0
          500 http://mirrors.linode.com/ubuntu/ trusty/main amd64 Packages

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