Created attachment 648268 [details]
patch

A private security bug was reported by Roman Fiedler against LXC.

The issue is embargoed and has not been disclosed publicly. We are
requesting a coordinated release date (CRD) of
<2015-09-29 14:00:00 UTC>. We ask that you keep this issue embargoed
until the CRD[1]. If nobody requests another date, Ubuntu and upstream
LXC will make the issue public on the CRD.

CVE-2015-1335 (https://launchpad.net/bugs/1476662) is a directory
traversal flaw that can occur while lxc-start is initially setting up
the mounts for a container.

If an attacker constructs a malicious symlink in the target path of a
container mount point, the symlink could be mishandled the next time the
container is started and the mount operation may be performed at an
undesired target location.

Additionally, if the source path of the mount is a malicious symlink
relative to the container, the symlink could be mishandled to bind mount
an undesired file or directory into the container.

Direct modification of the host's mount table is not possible since a
slave copy of the mount table is used.

An example of an attack that is made possible by this flaw is a user
inside of the container could leave behind a malicious symlink, at a
mount point target under their control, that would cause /proc/self/attr
to be mounted over. lxc-start would then unknowingly write to a "fake"
/proc/self/attr/current file, prior to launching the container init, to
perform an AppArmor profile transition. The profile transition would not
occur and the container init would run under incorrect confinement.

I've attached the fix from upstream LXC which applies against their git
master branch. Backported patches against the 1.1 and 1.0 trees will be
available upon request.

Tyler

[1] Please do not release a fix, make public revision control commits,
    comment in public bug reports or otherwise disclose information
    about this issue until the coordinated release date. This gives all
    affected parties a chance to release a fix at the same time.