Re: Container Networking for jails

From: Gijs Peskens <>
Date: Thu, 30 Jun 2022 07:18:11 UTC
I went with exactly the same design for the Docker port I started a while ago.
The reason I went with that design is that there weren't any facilities to modify a jails vent network configuration from outside of the jail. So it's needed to enter the jail, run ifconfig et all.
Linux jails will lack a compatible ifconfig. 
So having a parent FreeBSD based vnet jail ensures that networking can be configured for Linux children. 

There is a risk to using the / filesystem: users that might be allowed to setup and configure containers run standard system tools as root on the root filesystem, even if they might not have root permission themselves.. If an exploit was to be ever found in any of those tools to modify files that could be used as a step in a privilege escalation. 

Imho, that risk is acceptable in a first port, but should be documented. And ideally an option should be provided to use an alternative root if the user deems the risk unacceptable.

On 30 June 2022 09:04:24 CEST, Doug Rabson <> wrote:
>I wanted to get a quick sanity check for my current approach to
>networking with buildah and podman. These systems use CNI (
> to set up the network. This uses a sequence of
>'plugins' which are executables that perform successive steps in the
>process - a very common setup uses a 'bridge' plugin to add one half of
>epair to a bridge and put the other half into the container's vnet. IP
>addresses are managed by an 'ipam' plugin and an optional 'portmap'
>can be used to advertise container service ports on the host. All of
>plugins run on the host with root privileges.
>In kubernetes and podman, it is possible for more than one container to
>share a network namespace in a 'pod'. Each container in the pod can
>communicate with its peers directly via localhost and they all share a
>single IP address.
>Mapping this over to jails, I am using one vnet jail to manage the
>namespace and child jails of this to isolate the containers. The vnet
>uses '/' as its root path and the only things which run inside this
>are the CNI plugins. Using the host root means that a plugin can safely
>call host utilities such as ifconfig and route without having to trust
>container's version of them. An important factor here is that the CNI
>plugins will only be run strictly before the container (to set up) or
>strictly after (to tear down) - at no point will CNI plugins be
>executed at
>the same time as container executables.
>The child jails use ip4/6=inherit to share the vnet and each will use a
>root path to the container's contents in the same way as a normal
>non-hierarchical jail.
>Can anyone see any potential security problems here, particularly
>the use of nested jails? I believe that the only difference between
>setup and a regular non-nested jail is that the vnet outlives the
>briefly before it is torn down.

Verstuurd vanaf mijn Android apparaat met K-9 Mail. Excuseer mijn beknoptheid.