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[Launchpad Bug Tracker <1492570@xxxxxxxxxxxxxxxxxx>]

This bug was fixed in the package apport - 2.19-0ubuntu1

---------------
apport (2.19-0ubuntu1) wily; urgency=medium

  * New upstream release:
    - apport: Drop re-nicing. This might decrease the time a user has to wait
      for apport to finish the core dump for a crashed/hanging foreground
      process.  (See LP #1278780)
    - kernel_crashdump: Enforce that the log/dmesg files are not a symlink.
      This prevents normal users from pre-creating a symlink to the
      predictable .crash file, and thus triggering a "fill up disk" DoS attack
      when the .crash report tries to include itself. Thanks to halfdog for
      discovering this!  (CVE-2015-1338, part of LP #1492570)
    - SECURITY FIX: Fix all writers of report files (package_hook,
      kernel_crashdump, and similar) to open the report file exclusively,
      i. e.  fail if they already exist. This prevents privilege escalation
      through symlink attacks. Note that this will also prevent overwriting
      previous reports with the same same. Thanks to halfdog for discovering
      this!  (CVE-2015-1338, LP: #1492570)
    - apport: Ignore process restarts from systemd's watchdog. Their traces
      are usually useless as they don't have any information about the actual
      reasaon why processes hang (like VM suspends or kernel lockups with bad
      hardware) (LP: #1433320)

 -- Martin Pitt <martin.pitt@xxxxxxxxxx>  Thu, 24 Sep 2015 14:41:54
+0200

** Changed in: apport (Ubuntu Wily)
       Status: Fix Committed => Fix Released

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https://bugs.launchpad.net/bugs/1492570

Title:
  /usr/share/apport/kernel_crashdump accesses files in insecure manner

Status in Apport:
  Fix Released
Status in apport package in Ubuntu:
  Fix Released
Status in apport source package in Precise:
  Fix Released
Status in apport source package in Trusty:
  Fix Released
Status in apport source package in Vivid:
  Fix Released
Status in apport source package in Wily:
  Fix Released

Bug description:
  On Ubuntu Vivid Linux distribution upstart or SysV init invokes the
  program /usr/share/apport/kernel_crashdump at boot to prepare crash
  dump files for sending. This action is performed with root privileges.
  As the crash dump directory /var/crash/ is world writable and
  kernel_crashdump performs file access in unsafe manner, any local user
  may trigger a denial of service or escalate to root privileges. If
  symlink and hardlink protection is enabled (which should be the
  default for any modern system), only denial of service is possible.

  Problematic syscall in kernel_crashdump is:

  open("/var/crash/linux-image-3.19.0-18-generic.0.crash", O_WRONLY|O_CREAT|O_TRUNC|O_LARGEFILE|O_CLOEXEC, 0666) = 30
  ...
  open("/var/crash/vmcore.log", O_RDONLY|O_LARGEFILE|O_CLOEXEC) = 31

  Thus the output file is opened unconditionally and without O_EXCL or
  O_NOFOLLOW. Also opening of input file does not care about links.

  By sym- or hardlinking from the predictable dump file name to the
  vmcore.log, kernel_crashdump will recursively include its own dump as
  logfile, thus filling the disk. This also works with symlink and
  hardlink protection turned on.

  By symlinking to other files (with symlink protection off), arbitrary
  files can be overwritten to gain root privileges.

  # lsb_release -rd
  Description:    Ubuntu 15.04
  Release:        15.04

  # apt-cache policy apport
  apport:
    Installed: 2.17.2-0ubuntu1.3
    Candidate: 2.17.2-0ubuntu1.3
    Version table:
   *** 2.17.2-0ubuntu1.3 0
          500 http://archive.ubuntu.com/ubuntu/ vivid-updates/main i386 Packages
          100 /var/lib/dpkg/status
       2.17.2-0ubuntu1.1 0
          500 http://archive.ubuntu.com/ubuntu/ vivid-security/main i386 Packages
       2.17.2-0ubuntu1 0
          500 http://archive.ubuntu.com/ubuntu/ vivid/main i386 Packages

  
  See http://www.halfdog.net/Security/2015/ApportKernelCrashdumpFileAccessVulnerabilities/ for more information and follow the link on the bottom if you know what you are doing (user: InvitedOnly, pass: w0f63smR).

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  may be passed on (including password) to other security engineers
  under the same conditions at your own risk. Free circulation
  of that resource is allowed as soon as password protection was
  removed or when stated on the page itself.
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