Some others aren’t blockable as they would require blocking so many core features that the average container would become completely unusable. It provides a user experience similar to that of a public cloud. With it, you can easily mix and match both containers and virtual machines, sharing the same underlying storage and network. Note that when a script (such as either a hook script or anetwork interface up or down script) is called, the script’sstandard output is logged at level 1, debug. Note that without careful additional configuration of an LSM,sharing user+pid namespaces with a task may allow that task toescalate privileges to that of the task calling liblxc. Note that if two processes are in different user namespaces and oneprocess wants to inherit the other’s network namespace it usuallyneeds to inherit the user namespace as well.
As a convenience it also provides one default bridge on the system. To prevent this, untrusted users or containers ought to have entirely separate id maps (ideally of uids and gids each). We are aware of a number of exploits which will let you escape such containers and get full root privileges on the host. Some of those exploits can be trivially blocked and so we do update our different policies once made aware of them.
- Both lxd and lxc have the concept of unprivileged vs. privileged containers.
- I’m battling that one in my chef environment… there are several resources out there that call themselves ‘lxd’ but they are simple wrappers around around the lxc CLI tool and are not actually LXD.
- This configuration parameter can be specified multiple times; oncefor each environment variable you wish to configure.
- Privileged containers are containers that are created by root and run as root.
- Specifically, you need to manually allocate the subordinate uid and gid ranges to root in /etc/subuid and /etc/subgid and then set those ranges in /etc/lxc/default.conf using lxc.idmap entries.
NETWORK
Usually a cgroup hierarchy will have one or more”controllers” enabled. A “controller” in a cgroup hierarchy is usuallyresponsible for distributing a specific type of system resource alongthe hierarchy. Controllers include the “pids” controller, the “cpu”controller, the “memory” controller and others. Some controllershowever do not fall into the category of distributing a systemresource, instead they are often referred to as “utility” controllers.One utility controller is the device controller. Instead ofdistributing a system resource it allows to manage device access.
Features¶
In the legacy hierarchy the device controller was implemented like mostother controllers as a set of files that lxc coin could be written to. The legacy devicecontroller allowed the implementation of both “allowlists” and”denylists”. The kernel implementation of cgroups has changed significantly over theyears. With Linux 4.5 support for a new cgroup filesystem was addedusually referred to as “cgroup2” or “unified hierarchy”. Since then theold cgroup filesystem is usually referred to as “cgroup1″ or the”legacy hierarchies”.
Distribution LXC Documentation¶
- In most cases installing it is as simple as selecting it in your package manager.
- I would have learned lxc 1st because at one time that’s all there was.
- That means that if two containers share through identical or overlapping id maps, a common kernel uid, then they also share limits, meaning that a user in a first container can effectively DoS the same user in another container.
- Note that when a script (such as either a hook script or anetwork interface up or down script) is called, the script’sstandard output is logged at level 1, debug.
Absolute path from container rootfs to the binary to run by default. This configuration options can be set to to specify the default binary for application container started via the execute() API call and accompanies the system container based lxc.init.cmd configuration key. To pass the arguments in new style via environment variables set to 1 otherwise set to 0 to pass them as arguments. This setting affects all hooks arguments that were traditionally passed as arguments to the script. Specifically, it affects the container name, section (e.g. ‘lxc’, ‘net’) and hook type (e.g. ‘clone’, ‘mount’, ‘pre-mount’) arguments.
This had the unfortunate side effect of allowing a user in the container to effectively write as much data as they wanted on the host, possibly bypassing quotas in place for the container. LXC removed the cgmanager and cgfs legacy cgroup drivers cleaning up a lot of code in the process. One of my goals is to set up a dual-distro system on my laptop with Ubuntu and Slackware (maybe also some others like Centos, Debian, and/or Fedora). And part of that goal is to have both Ubuntu and Slackware each running in their own container with the host system minimized to run containers and suitable system administrator tools. And i also want to look into building “distros” targeted to only be container images. Indeed, an issue with lxd init is that as a wizard, it applies each choice as you go along.
Please see the cgroups manual page for a detailedexplanation of the differences between the two versions. With AppArmor disabled, privileged containers should be considered as entirely unsafe. While we don’t consider them to be root safe when apparmor is present, we also don’t know of a trivial way to escape in that case, but without apparmor it’s downright trivial. For interacting with the daemon (to create and manage containers, for instance), you want to use the lxc command. A container’s file system activity is restricted to /var/lib/lxc//rootfs. When a container is destroyed all of /var/lib/lxc/ is also destroyed.
New Configuration Keys
Both lxd and lxc have the concept of unprivileged vs. privileged containers. Both the default log level and the log file can be specified in thecontainer configuration file, overriding the default behavior. Notethat the configuration file entries can in turn be overridden by thecommand line options to lxc-start. Implements an allowlist device program, i.e. the kernel will blockaccess to all devices not specifically allowed in this list. Thisparticular program states that all character and block devices may becreated but only /dev/null might be read or written. At its core a cgroup hierarchy is a way to hierarchically organizeprocesses.
console_log()
To do this, it uses the functionality provided by the kernel running on the host system. Incus is image based and provides images for a wide number of Linux distributions. In version 2, the policy may be denylist or allowlist,supports per-rule and per-policy default actions, and supportsper-architecture system call resolution from textual names.
If cgroup namespaces are enabled, then any cgroupauto-mounting request will be ignored, since the container canmount the filesystems itself, and automounting can confuse thecontainer init. LXC inherits cgroup limits from its parent, on my Linux distribution, there are no real limits set. As a result, a user in a container can reasonably easily DoS the host by running a fork bomb, by using all the system’s memory or creating network interfaces until the kernel runs out of memory. As privileged containers are considered unsafe, we typically will not consider new container escape exploits to be security issues worthy of a CVE and quick fix.
Note that sharing pid namespaces will likely not work with most initsystems. Note that when mounting a filesystem from animage file or block device the third field (fs_vfstype)cannot be auto as withmount(8)but must be explicitly specified. Standard output from the script is logged at debug level.Standard error is not logged, but can be captured by thehook redirecting its standard error to standard output. That is, containers which offer anenvironment as close as possible as the one you’d get from a VM butwithout the overhead that comes with running a separate kernel andsimulating all the hardware. For migration optimization features like pre-copy or post-copy migration the support cannot be determined by simply looking at the CRIU version.
The lxc-update-config tool can be used to convert an older, now invalid, configuration to the new format. LXD is a nice project and allows to use LXC containers very easily! The only downside is that it only works perfectly on Ubuntu Server. Do you know if there’s a way for either admins or other trusted users to edit this post? Also, with the link limit now bumped to 5 for new users, you should be able to edit it and add the remaining link. Outside of Ubuntu, it’s a bit easier to deploy LXC than LXD on distros completely outside the Debian/Ubuntu ecosystem, because it has fewer dependencies on kernel features and patches.