guide about installing a Debian remotely with full disk encryption

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LUXEY Adrien 2021-03-04 12:01:33 +01:00
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Go to [deployer](deployer/), where the fun is at. Go to [deployer](deployer/), where the fun is at.
## Structure
* [`/deployer`](deployer/) contains deployment Ansible code for Serenity. **Being outdated** by migration to new server (HammerHead).
* [`/bootstrapper`](bootstrapper/) contains Ansible configuration code for new servers (notably HammerHead). Will only take interest in the bootstrapping phase of the host. Service deployment will be handled by Nomad et al.
## TODO ## TODO
* dockerise nextcloud, synapse, gitea * Host bootstrap Ansible code to [`/bootstrapper`](bootstrapper/)
* backup db
* send backups to a remote
# Random notes # Random notes

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# Bootstrap cluster hosts
* `os_install/` contains documentation about OS installation for remote nodes
* The rest is Ansible configuration
## Configuration goals
* Configure access rights
User creation, upload their ssh keys, set passwordless sudo...
* Installation of base toolset through package manager
* Installation of complex tooling (e.g. Docker, Nomad, Vault, Consul) through other means (custom APT repo?)
* Basic configuration of the server
* Docker log rotation

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# Installing a cloud server with full disk encryption
For hosting purposes, I am installing a new server on [Kimsufi](kimsufi.com/). This is a French public cloud provider (property of [OVH](ovh.com/)).
It is well known that, at [Deuxfleurs](https://deuxfleurs.fr), we do not fancy hosting in datacenters: because of the lack on control on our machines, and potential privacy threats. In essence, people at Kimsufi could easily -- and without me knowing -- read my hard drive, and thus any sensitive user data stored inside.
For that reason, I want to make it harder for their staff to access my data. A good first line of defense for that purpose is to encrypt the whole disk (*aka* Full Disk Encryption). Note that motivated attackers with physical access to my server would easily overcome the encryption. **If you really care about who accesses your data, keep your hard drives closest to you, e.g. at your home.**
---
Long story short: this guide presents a step-by-step installation of Debian buster on Kimsufi, using the [`dm-crypt`](https://wiki.archlinux.org/index.php/Dm-crypt) Linux kernel subsystem to encrypt the `/` and the `swap` partitions.
Because I don't have physical access to the server, I need a way to *remotely enter the disk decryption password*, that is `dropbear` (a lightweight SSH server) inside `initramfs` (a minimal operating system that runs from RAM, before Linux boots).
If you plan on doing the same without Kimsufi, know that it makes no difference: I am basically using a "rescue" console on another computer to configure `/dev/sda` (my server's system drive) for booting Linux with encrypted partitions.
I must credit several useful guides that helped me succeed:
* [OpsBlog guide on installing Linux with full-disk encryption and DropBear SSH on Kimsufi](https://opsblog.net/posts/full-disk-encrypted-ubuntu-kimsufi-sever/)
DropBear allows SSH connection before boot, to remotely decrypt the main partition.
* [Debian guide on installing Debian from a Linux system](https://www.debian.org/releases/wheezy/mipsel/apds03.html.en)
## Overview of steps
* Boot the Kimsufi server in rescue mode (gives you a remote shell with access to your system's hard drive).
* Wipe filesystem, format partitions. I basically want:
* A "cleartext" `/boot` partition
* An encrypted `/` partition
* An encrypted swap partition
Docs on the encrypted swap:
* [ArchLinux wiki: dm-crypt - Swap encryption](https://wiki.archlinux.org/index.php/Dm-crypt/Swap_encryption)
* [cryptsetup FAQ](https://gitlab.com/cryptsetup/cryptsetup/-/wikis/FrequentlyAskedQuestions#2-setup): see "2.3 How do I set up encrypted swap?"
* Install and configure Debian (including disk cryptography and decryption through SSH).
* Boot and log into the server.
* Setup automated decryption from a remote (in case of reboot).
## Detailed process
### Boot the server in rescue mode
* Go to the Kimsufi admin panel, click "NetBoot", select "Rescue", pick "rescue64-pro", clock "Next", "Confirm", and then click the "Reboot" button on the admin panel.
* Kimsufi will mail you the root password for you to log into the server in rescue mode.
* Will likely cause an error from your SSH client, since the fingerprint of the server differs from the usual one.
You should end up with a shell that has access to `/dev/sda`, your server's drive.
### Wipe filesystem & format partitions
Target partition table:
```
+-----------+--------------------+-----------+--------------------+
Name: | /dev/sda1 | /dev/sda2 | /dev/sda3 | /dev/sda4 |
| | | | |
| | | | |
| | +------------------+ | +------------------+
| | | /dev/mapper/swap | | | /dev/mapper/main |
Format: | none | | swap | ext4 | | ext4 |
Size: | 1MiB | | 8GiB | 512MiB | | remaining space |
Flags: | bios_grub | | | | | |
Mount: | | | swap | /boot | | / |
+-----------+-+------------------+-----------+-+------------------+
```
We use GPT partition table layout (without UEFI), which demands a small `bios_grub` partition at the beginning of the drive (stores GRUB's `core.img`). Hence `/dev/sda1`. See:
* [Wikipedia: BIOS boot partition](https://en.wikipedia.org/wiki/BIOS_boot_partition)
* [GNU: BIOS installation](https://www.gnu.org/software/grub/manual/grub/html_node/BIOS-installation.html#BIOS-installation)
* [ArchLinux wiki: Partitioning](https://wiki.archlinux.org/index.php/partitioning#Partition_table)
* [Gentoo wiki: Installation - Disks](https://wiki.gentoo.org/wiki/Handbook:AMD64/Installation/Disks#Partition_tables)
* Wipe all information about previous filesystem:
DANGER!!! DANGER!!! WIPES EVERYTHING FROM YOUR DISK!!!
```bash
wipefs -a /dev/sda
```
* Create GPT disk layout
```bash
# Create GPT layout
parted -a optimal /dev/sda mklabel gpt
# Create first 1MiB bios_grub partition
parted /dev/sda -a optimal mkpart bios_grub 0% 1MiB
parted /dev/sda set 1 bios_grub on
# Create third 8GiB swap partition
parted /dev/sda -a optimal mkpart swap 1MiB 8001MiB
# Create second 512MiB /boot partition
parted /dev/sda -a optimal mkpart boot 8001MiB 8513MiB
# Create last / partition using all remaining space
parted /dev/sda -a optimal mkpart main 8513MiB 100%
# Set first partition as bootable
```
* Format partitions
* The ext4 boot partition
Format it like so:
```bash
mkfs.ext4 /dev/sda3
```
* The encrypted swap partition
All configuration of the encrypted swap partition comes after the OS installation.
* The encrypted main partition
```bash
# Set it up using cryptsetup (I searched for good parameters):
cryptsetup --type luks2 --cipher aes-xts-plain64 --hash sha256 --iter-time 2000 --key-size 512 luksFormat /dev/sda4
# Get the UUID, save it for later:
cryptsetup luksDump /dev/sda4 | grep UUID | awk '{print $2}'
# Example output: 09762476-ba7c-4732-8856-44a716c23339
# Decrypt the partition:
cryptsetup open /dev/sda4 main
# Format it to ext4:
mkfs.ext4 /dev/mapper/main
```
### Install and configure Debian
* Mount the partitions
```bash
# Decrypt the main partition (if not already done):
cryptsetup open /dev/sda4 main
# mount it:
mount /dev/mapper/main /mnt
# Mount the boot partition:
mkdir /mnt/boot
mount /dev/sda3 /mnt/boot
```
* Bootstrap latest stable Debian into mounted partitions
```bash
debootstrap --arch amd64 stable /mnt http://ftp.fr.debian.org/debian/
```
* Mount system partitions
```bash
mount -o bind /dev /mnt/dev
mount -t proc proc /mnt/proc
mount -t sysfs sys /mnt/sys
mount -t devpts devpts /mnt/dev/pts
```
* Chroot
chroot /mnt /bin/bash
* Fill out `crypttab` and `fstab` (`UUID` is the output of above `cryptsetup luksDump`)
`/etc/crypttab`
```bash
cat << EOF > /etc/crypttab
# <name> <device> <password> <options>
main UUID=09762476-ba7c-4732-8856-44a716c23339 none luks
swap /dev/sda2 /dev/urandom swap,noearly,cipher=aes-xts-plain64,size=512
EOF
```
`/etc/fstab`
```bash
cat << EOF > /etc/fstab
# <filesystem> <dir> <type> <options> <dump> <pass>
/dev/mapper/main / ext4 errors=remount-ro 0 1
/dev/sda3 /boot ext4 defaults 0 2
/dev/mapper/swap none swap sw 0 0
EOF
```
* Do the `/proc/mounts` -> `/etc/mtab` symlink
```bash
ln -s /proc/mounts /etc/mtab
```
Why? [Linux From Stratch](http://archive.linuxfromscratch.org/lfs-museum/3.3/LFS-BOOK-3.3-HTML/chapter06/mtablink.html) and [our guide on OpsBlog](https://opsblog.net/posts/full-disk-encrypted-ubuntu-kimsufi-sever/) both say it's needed.
* Choose a hostname & DNS domain
hammerhead & hammerhead.luxeylab.net
* Fill in network-related files
Beware of your ethernet interface name! It's only after failing with `eth0` that the boot logs informed me that the iface name was `eno1`.
`/etc/network/interfaces`
```bash
cat << EOF > /etc/network/interfaces
######################################################################
# /etc/network/interfaces -- configuration file for ifup(8), ifdown(8)
# See the interfaces(5) manpage for information on what options are
# available.
######################################################################
# loopback interface
auto lo
iface lo inet loopback
# eno1 through DHCP
auto eno1
iface eno1 inet dhcp
EOF
```
`/etc/resolv.conf`
```bash
cat << EOF > /etc/resolv.conf
# OVH public DNS
nameserver 213.186.33.99
# https://servers.opennicproject.org/edit.php?srv=ns2.he.de.dns.opennic.glue
nameserver 172.104.136.243
EOF
```
`/etc/hosts`
```bash
cat << EOF > /etc/hosts
127.0.0.1 localhost
127.0.1.1 hammerhead hammerhead.luxeylab.net
# The following lines are desirable for IPv6 capable hosts
::1 localhost ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
ff02::3 ip6-allhosts
213.186.33.116 ws.ovh.com
198.245.48.4 ws.ovh.ca
5.135.179.11 hammerhead hammerhead.luxeylab.net
EOF
```
`/etc/hostname`
```bash
echo "hammerhead" > /etc/hostname
```
`/etc/timezone`
```bash
dpkg-reconfigure tzdata
```
* Update APT repositories in `/etc/apt/sources.list`
```bash
cat << EOF > /etc/apt/sources.list
deb http://ftp.fr.debian.org/debian buster main
deb-src http://ftp.fr.debian.org/debian buster main
deb http://ftp.fr.debian.org/debian-security/ buster/updates main
deb-src http://ftp.fr.debian.org/debian-security/ buster/updates main
deb http://ftp.fr.debian.org/debian buster-updates main
deb-src http://ftp.fr.debian.org/debian buster-updates main
EOF
```
* Configure locales & keyboard
```bash
# Refresh packages list
apt update
# Install & configure locales
apt install locales && dpkg-reconfigure locales
# Install & configure keyboard
apt install console-setup console-data && dpkg-reconfigure keyboard-configuration
```
* Pick up a kernel & install it
```bash
apt-cache search linux-image
# I selected the meta-package `linux-image-amd64` which is the latest
apt install linux-image-amd64 linux-headers-amd64
```
* Install additional necessary software
```bash
apt install cryptsetup dropbear grub-pc man-db ssh
```
Because we use a GPT table layout but no UEFI, we install `grub-pc` and not `grub-efi-amd64`.
Do think about installing `bash-completion` and `ufw` someday.
* Set up SSH keys and the rest (where `<PUBLIC_SSH_KEY>` is your client SSH public key)
```bash
mkdir /root/.ssh && chmod 600 /root/.ssh
echo "<PUBLIC_SSH_KEY>" > /root/.ssh/authorized_keys
echo "<PUBLIC_SSH_KEY>" > /etc/dropbear-initramfs/authorized_keys
```
* Configure dropbear-initramfs (SSH on boot)
```bash
sed -i 's/#DROPBEAR_OPTIONS=/DROPBEAR_OPTIONS=\"-p 2222 -c \/bin\/cryptroot-unlock\"/' /etc/dropbear-initramfs/config
```
This changes the SSH listen post to 2222, and enforces that the only command run from `dropbear-initramfs` is `cryptroot-unlock`.
* Configure sshd custom listen port (SSH after boot)
```bash
sed -i 's/#Port 22/Port 2223/' /etc/ssh/sshd_config
```
* [Optional] Authorize root password login
```bash
# Remove -s (disable password login) from dropbear-initramfs
sed -i 's/local flags=\"Fs\"/local flags=\"F\"/' /usr/share/initramfs-tools/scripts/init-premount/dropbear
```
* Update GRUB and initramfs
```bash
update-grub && update-initramfs -u
```
* Clean up before leaving
```bash
exit
umount /mnt/{boot,dev/pts,dev,proc,sys}
umount /mnt
cryptsetup luksClose main
```
### Boot and log into the server
* I configured my laptop's `~/.ssh/config` like so:
```
Host hammerhead-decrypt
User root
Hostname <SERVER_URL_OR_IP>
Port 2222
IdentityFile <PRIVATE_SSH_KEY_PATH>
# Prevents signatures mismatch
UserKnownHostsFile ~/.ssh/known_hosts_hammerhead-decrypt
Host hammerhead
User root
Hostname <SERVER_URL_OR_IP>
Port 2223
IdentityFile <PRIVATE_SSH_KEY_PATH>
```
* And here is how I connect to the server:
```bash
laptop$ ssh hammerhead-decrypt
Please unlock disk main: <PASSWORD>
# [...]
Connection to <SERVER_URL_OR_IP> closed.
laptop$ ssh hammerhead
# [...]
root@hamerhead:~# echo A winner is you!
A winner is you!
```
### Setup automated decryption from a remote
It is desirable to have a daemon running on a remote server, to automatically decrypt the drive when the encrypted server reboots without warning.
The remote server is called a *key escrow*. One must be particularly careful about the escrow's security, since it holds the decryption keys for our server.
Trinity recommends [Tang](https://github.com/latchset/tang) and [Clevis](https://github.com/latchset/clevis).