[Bug 1675163] Re: Don't attempt to create devices in LXC containers

[Stéphane Graber]

root at makedev-16-04:~# apt install makedev
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages will be upgraded:
  makedev
1 upgraded, 0 newly installed, 0 to remove and 12 not upgraded.
Need to get 24.4 kB of archives.
After this operation, 29.7 kB disk space will be freed.
Get:1 http://archive.ubuntu.com/ubuntu xenial-proposed/main amd64 makedev all 2.3.1-93ubuntu2~ubuntu16.04.1 [24.4 kB]
Fetched 24.4 kB in 0s (55.5 kB/s)
(Reading database ... 13025 files and directories currently installed.)
Preparing to unpack .../makedev_2.3.1-93ubuntu2~ubuntu16.04.1_all.deb ...
Unpacking makedev (2.3.1-93ubuntu2~ubuntu16.04.1) over (2.3.1-93ubuntu1) ...
Setting up makedev (2.3.1-93ubuntu2~ubuntu16.04.1) ...
LXC container detected, aborting due to LXC managed /dev.
root at makedev-16-04:~# 

Ubuntu 16.04 too.

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https://bugs.launchpad.net/bugs/1675163

Title:
  Don't attempt to create devices in LXC containers

Status in makedev package in Ubuntu:
  Fix Released
Status in makedev source package in Precise:
  Fix Committed
Status in makedev source package in Trusty:
  Fix Committed
Status in makedev source package in Xenial:
  Fix Committed
Status in makedev source package in Yakkety:
  Fix Committed
Status in makedev source package in Zesty:
  Fix Released

Bug description:
  Right now the "makedev" postinst script will attempt to create a
  number of devices in /dev, failing the package upgrade should any of
  those mknod calls fail.

  LXC containers, especially unprivileged ones do not allow the use of
  mknod, making it impossible to upgrade makedev in those containers and
  preventing Ubuntu release upgrades.

  The fix is quite simple, detect that we are running in an LXC
  container and skip the rest of the postinst script as is done in a
  number of other cases.

  = SRU
  == Rationale
  This issue prevents release to release upgrades in unprivileged LXC containers when makedev is part of the upgraded set. This is currently visible when upgrading from Ubuntu 12.04 to Ubuntu 14.04.

  == Testcase
  Install the new package in an unprivileged container. With LXD, simply use "lxc launch ubuntu:<series> test" to create the container.

  Prior to this fix, the upgrade will fail on some mknod errors, after
  it, it'll go on after printing a message indicating that LXC was
  detected.

  == Regression potential
  The detection logic is based on PID 1's environment containing a container=lxc entry. If a non-LXC system somehow had that set, it'd lead to the makedev upgrade no longer creating extra devices. This is unlikely to really matter though since the system is clearly already functioning properly at that point.

  Similarly, some privileged LXC containers can be configured in a way
  where mknod is possible, this update will still disable the postinst
  for those cases as short of attempting every mknod ahead of time,
  there is no reliable way to detect any seccomp or apparmor policy in
  play.

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