VoidLinux in FreeBSD Jail; with init

Posted on Aug 21, 2021

Two important things happened this week for me.

First, Faraz asked me if I can rename my Jail manager to something other than Jailio because he got that domain for his Jailer manager already. So I named it

Second, I was able to run a complete Linux system using Jailer. While the repo for Jailer is not released yet (we are auditing for possible security issues), I would like to share how I was able to run VoidLinux in a Jail.

Since Jailer is not announced yet, I will give the examples using jail.conf, as most people either are or should be familiar with its concepts.

I went with VoidLinux because I am able to run the init process without its need to be running as PID1.

Let’s start, shall we?

First, ZFS dataset for our jail!

zfs create zroot/jails/voidlinux

Next we need to fetch the base system of VoidLinux. Luckily they do provide it on their website.

fetch https://alpha.de.repo.voidlinux.org/live/current/void-x86_64-ROOTFS-20210218.tar.xz

Now we can extract this into our dataset

tar xf void-x86_64-ROOTFS-20210218.tar.xz -C /usr/local/jails/voidlinux/

You might get an error that ./usr/bin/iputils-ping: Cannot restore extended attributes: security.capability, which is fine, I think?

If you are on FreeBSD 12.2-RELEASE or later, now you need to enable the Linuxulator.

service linux enable; service linux start

Now you can at least chroot into the system.

chroot /usr/local/jails/voidlinux/ /bin/bash

If everything is fine until now, perfect.

Now we need to add a root user into the system.

root@host:~ # cd /usr/local/jails/voidlinux/etc/
root@host:/usr/local/jails/voidlinux/etc # echo "root::0:0::0:0:Charlie &:/root:/bin/bash" > master.passwd
root@host:/usr/local/jails/voidlinux/etc # pwd_mkdb -d ./ -p master.passwd
pwd_mkdb: warning, unknown root shell

Execute the rest of the commands in Void.

root@host:~ # chroot /usr/local/jails/voidlinux/ /bin/bash
bash-5.1# cd /etc/
bash-5.1# pwconv 
bash-5.1# grpconv 
bash-5.1# passwd 
New password: 
Retype new password: 
passwd: password updated successfully
bash-5.1# exit

If all went fine, then the system is ready to be run as a Jail!

First we need to make an fstab for the system.

Create a file at /usr/local/jails/voidlinux/etc/fstab.pre and insert the following inside

devfs       /usr/local/jails/voidlinux/dev      devfs           rw                      0   0
tmpfs       /usr/local/jails/voidlinux/dev/shm  tmpfs           rw,size=1g,mode=1777    0   0
fdescfs     /usr/local/jails/voidlinux/dev/fd   fdescfs         rw,linrdlnk             0   0
linprocfs   /usr/local/jails/voidlinux/proc     linprocfs       rw                      0   0
linsysfs    /usr/local/jails/voidlinux/sys      linsysfs        rw                      0   0
/tmp        /usr/local/jails/voidlinux/tmp      nullfs          rw                      0   0

Next, let’s create a loopback interface for networking. Oh yes, VNET is not supported yet, but I’m working on a patch :)

ifconfig lo1 create
ifconfig lo1 inet 10.10.0.1/24 up # sorry, 10.0.0.0/24 was unavailable :P

Okay, time to create our Jail conf!

exec.clean;
allow.raw_sockets;
mount.devfs;

voidlinux {
    $id     = "1";
    $ipaddr = "10.10.0.42";
    $mask   = "255.255.255.0";
    $domain = "srv0.bsd.am";
    devfs_ruleset  = 4;
    allow.mount;
    allow.mount.devfs;
    mount.fstab = "${path}/etc/fstab.pre";

    exec.start     = "/bin/sh /etc/runit/2 &";
    exec.stop      = "/bin/sh /etc/runit/3";


    ip4.addr      = "${ipaddr}";
    interface     = "lo1";
    host.hostname = "${name}.${domain}";
    path = "/usr/local/jails/voidlinux";
    exec.consolelog = "/var/log/jail-${name}.log";
    persist;
    allow.socket_af;
}

Let’s check?

# jls
   JID  IP Address      Hostname                      Path
     1  192.168.0.42    voidlinux.srv0.bsd.am         /usr/local/jails/voidlinux

And the process tree?

# ps auxd -J voidlinux
USER   PID %CPU %MEM  VSZ  RSS TT  STAT STARTED    TIME COMMAND
root 35182  0.0  0.1 2320 1428  -  SsJ  21:09   0:00.12 runsvdir -P /run/runit/runsvdir/current log: ot set SO_PASSCRED: Protocol not available\ncould not set SO_PASSCRED: Protocol
root 35190  0.0  0.1 2168 1376  -  SsJ  21:09   0:00.02 - runsv agetty-tty6
root 35397  0.0  0.1 2412 1704  -  SsJ  21:10   0:00.00 `-- agetty tty6 38400 linux
root 35191  0.0  0.1 2168 1376  -  SsJ  21:09   0:00.02 - runsv agetty-tty1
root 35396  0.0  0.1 2412 1704  -  SsJ  21:10   0:00.00 `-- agetty --noclear tty1 38400 linux
root 35192  0.0  0.1 2168 1376  -  SsJ  21:09   0:00.02 - runsv agetty-tty5
root 35398  0.0  0.1 2412 1704  -  SsJ  21:10   0:00.01 `-- agetty tty5 38400 linux
root 35193  0.0  0.1 2168 1376  -  SsJ  21:09   0:00.02 - runsv agetty-tty2
root 35393  0.0  0.1 2412 1704  -  SsJ  21:10   0:00.00 `-- agetty tty2 38400 linux
root 35194  0.0  0.1 2168 1396  -  RsJ  21:09   0:00.12 - runsv udevd
root 35195  0.0  0.1 2168 1376  -  SsJ  21:09   0:00.02 - runsv agetty-tty3
root 35394  0.0  0.1 2412 1704  -  SsJ  21:10   0:00.00 `-- agetty tty3 38400 linux
root 35196  0.0  0.1 2168 1376  -  SsJ  21:09   0:00.02 - runsv agetty-tty4
root 35390  0.0  0.1 2412 1704  -  SsJ  21:10   0:00.00 `-- agetty tty4 38400 linux

You may jexec now :)

# jexec voidlinux /bin/bash
bash-5.1# uname -a
Linux voidlinux.srv0.bsd.am 3.2.0 FreeBSD 12.2-RELEASE-p6 GENERIC x86_64 GNU/Linux

Let’s check networking?

bash-5.1# ping -c 1 10.10.0.1
ping: WARNING: setsockopt(ICMP_FILTER): Protocol not available
PING 10.10.0.1 (10.10.0.1) 56(84) bytes of data.
64 bytes from 10.10.0.1: icmp_seq=1 ttl=64 time=0.069 ms

--- 10.10.0.1 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.069/0.069/0.069/0.000 ms

There you go! Well, things that are related to netlink might not work, but other than that it’s okay.

I did have some problems while installing packages, something about too many levels of symbolic links. Here’s the exact output when I was trying to install the curl package

[*] Unpacking packages
libev-4.33_1: unpacking ...
ERROR: libev-4.33_1: [unpack] failed to extract file `./usr/lib/libev.so.4': Too many levels of symbolic links
ERROR: libev-4.33_1: [unpack] failed to extract files: Too many levels of symbolic links
ERROR: libev-4.33_1: [unpack] failed to unpack files from archive: Too many levels of symbolic links
Transaction failed! see above for errors.

Now, I did not find the time to fix this yet, but if you have any idea, please let me know or comment below :)

So, what do we have here? A Linux Jail, running VoidLinux, with init, so you can also run services, and basic networking for it.

That’s all folks…