[Bug 1738427] [NEW] Segfault if crontab is owned by a user who cannot be found?

[Sitsofe Wheeler]

Public bug reported:

Description of the problem
It appears that cron will go on to crash if it finds a crontab owned by uid who does not map to a valid user.

Steps to reproduce:
1. Create a crontab with an Active Directory user set up via SSSD?
2. Switch AD domains so user's uid is entirely different?
3. Wait for cron to try and run the old user's crontab?

Expected result:
Error in the journal?

Actual result:
Error in the log file and cron segfault?

How reproducible is the issue?
It has happened twice so far before the crontab was removed.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: cron 3.0pl1-128ubuntu2
ProcVersionSignature: Ubuntu 4.4.0-103.126-generic 4.4.98
Uname: Linux 4.4.0-103-generic x86_64
NonfreeKernelModules: zfs zunicode zcommon znvpair zavl
ApportVersion: 2.20.1-0ubuntu2.14
Architecture: amd64
Date: Fri Dec 15 14:33:45 2017
InstallationDate: Installed on 2017-03-09 (280 days ago)
InstallationMedia: Ubuntu-Server 16.04.2 LTS "Xenial Xerus" - Release amd64 (20170215.8)
ProcEnviron:
 LANGUAGE=en_GB:en
 TERM=xterm-256color
 PATH=(custom, no user)
 LANG=en_GB.UTF-8
 SHELL=/bin/bash
SourcePackage: cron
UpgradeStatus: No upgrade log present (probably fresh install)

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


** Tags: amd64 apport-bug xenial

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https://bugs.launchpad.net/bugs/1738427

Title:
  Segfault if crontab is owned by a user who cannot be found?

Status in cron package in Ubuntu:
  New

Bug description:
  Description of the problem
  It appears that cron will go on to crash if it finds a crontab owned by uid who does not map to a valid user.

  Steps to reproduce:
  1. Create a crontab with an Active Directory user set up via SSSD?
  2. Switch AD domains so user's uid is entirely different?
  3. Wait for cron to try and run the old user's crontab?

  Expected result:
  Error in the journal?

  Actual result:
  Error in the log file and cron segfault?

  How reproducible is the issue?
  It has happened twice so far before the crontab was removed.

  ProblemType: Bug
  DistroRelease: Ubuntu 16.04
  Package: cron 3.0pl1-128ubuntu2
  ProcVersionSignature: Ubuntu 4.4.0-103.126-generic 4.4.98
  Uname: Linux 4.4.0-103-generic x86_64
  NonfreeKernelModules: zfs zunicode zcommon znvpair zavl
  ApportVersion: 2.20.1-0ubuntu2.14
  Architecture: amd64
  Date: Fri Dec 15 14:33:45 2017
  InstallationDate: Installed on 2017-03-09 (280 days ago)
  InstallationMedia: Ubuntu-Server 16.04.2 LTS "Xenial Xerus" - Release amd64 (20170215.8)
  ProcEnviron:
   LANGUAGE=en_GB:en
   TERM=xterm-256color
   PATH=(custom, no user)
   LANG=en_GB.UTF-8
   SHELL=/bin/bash
  SourcePackage: cron
  UpgradeStatus: No upgrade log present (probably fresh install)

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