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[Tyler Hicks <tyhicks@xxxxxxxxxxxxx>]

Note that the severity of this issue is lower than the similar issue
that was discovered in overlayfs since the aufs module has to be loaded
with the 'allow_userns' parameter.

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https://bugs.launchpad.net/bugs/1547400

Title:
  aufs fails to handle sanitize xattrs in workdir, copies SUID binaries
  from no-suid fuse mounts

Status in Linux:
  Confirmed
Status in linux package in Ubuntu:
  Confirmed

Bug description:
  When aufs module is loaded with "modprobe aufs allow_userns",
  unprivileged user can use xattrs on the working directory or aufs
  mount over a fuse mount to create SUID/SGID binaries, thus escalating
  privileges. These errors are quite similar to those on overlayfs:

  https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1535150
  https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1534961

  aufs developers have already confirmed and issued a fix:

  https://sourceforge.net/p/aufs/mailman/message/34864744/

  Specific reproducers can be found at:

  http://www.halfdog.net/Security/2016/AufsPrivilegeEscalationInUserNamespaces/
  InvitedOnly AkgY8iqF

  # lsb_release -rd
  Description:    Ubuntu 15.10
  Release:        15.10

  # apt-cache policy linux-image-4.2.0-27-generic
  linux-image-4.2.0-27-generic:
    Installed: 4.2.0-27.32
    Candidate: 4.2.0-27.32
    Version table:
   *** 4.2.0-27.32 0
          500 http://archive.ubuntu.com/ubuntu/ wily-updates/main amd64 Packages
          500 http://archive.ubuntu.com/ubuntu/ wily-security/main amd64 Packages
          100 /var/lib/dpkg/status

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