Unhandled exception in run_hang()

[Seong-Joong Kim]

## Description
When we start apport-cli without PID, an unhandled exception in apport 2.20.11 and earlier may allow an authenticated user to potentially enable a denial of service via local access.

The following command may cause an application crash due to an unhandled exception.

$ apport-cli --hanging

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Problem report file: /tmp/apport.apport.uc0_znhj.apport
Traceback (most recent call last):
  File "/usr/bin/apport-cli", line 387, in <module>
    if not app.run_argv():
  File "/usr/lib/python3/dist-packages/apport/ui.py", line 690, in run_argv
    self.run_hang(self.options.pid)
  File "/usr/lib/python3/dist-packages/apport/ui.py", line 410, in run_hang
    os.kill(int(pid), signal.SIGKILL)
TypeError: int() argument must be a string, a bytes-like object or a number, not 'NoneType'

Above command generates the following application crash file in /var/crash/ directory.

ProblemType: Crash
CurrentDesktop: ubuntu:GNOME
Date: Sun May 3 19:09:41 2020
ExecutablePath: /usr/bin/apport-cli
ExecutableTimestamp: 1585099033
InterpreterPath: /usr/bin/python3.6
ProcCmdline: /usr/bin/python3 /usr/bin/apport-cli --hanging
ProcCwd: /home/user/apport/bin
ProcEnviron:
 ...
ProcMaps:
 ...
ProcStatus:
 ...
PythonArgs: ['/usr/bin/apport-cli', '--hanging']
Traceback:
 Traceback (most recent call last):
   File "/usr/bin/apport-cli", line 387, in <module>
     if not app.run_argv():
   File "/usr/lib/python3/dist-packages/apport/ui.py", line 690, in run_argv
     self.run_hang(self.options.pid)
   File "/usr/lib/python3/dist-packages/apport/ui.py", line 410, in run_hang
     os.kill(int(pid), signal.SIGKILL)
 TypeError: int() argument must be a string, a bytes-like object or a number, not 'NoneType'
UserGroups: adm cdrom dip lpadmin plugdev sambashare sudo
_LogindSession: 6

Many thanks.

[Launchpad Janitor (janitor)]

This bug was fixed in the package apport - 2.20.11-0ubuntu27.6

---------------
apport (2.20.11-0ubuntu27.6) focal-security; urgency=medium

  * SECURITY UPDATE: information disclosure issue (LP: #1885633)
    - data/apport: also drop gid when checking if user session is closing.
    - CVE-2020-11936
  * SECURITY UPDATE: crash via malformed ignore file (LP: #1877023)
    - apport/report.py: don't crash on malformed mtime values.
    - CVE-2020-15701
  * SECURITY UPDATE: TOCTOU in core file location
    - data/apport: make sure the process hasn't been replaced after Apport
      has started.
    - CVE-2020-15702
  * apport/ui.py, test/test_ui.py: make sure a PID is specified when using
    --hanging (LP: #1876659)
  * WARNING: This package does _not_ contain the changes from
    2.20.11-0ubuntu27.5 in focal-proposed.

 -- Marc Deslauriers <email address hidden> Fri, 31 Jul 2020 09:10:30 -0400