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commit 85b54e2c9e5041d1485720d887aa878cab6d33f6 (patch)
parent 6c6d8e0872a8f32f407a3e7896d67a6eb03c7ae1
Author: Alex Karle <alex@alexkarle.com>
Date:   Mon, 13 Jun 2022 22:51:03 -0400

blog: Add post on wggen tool to manage wg creds

Diffstat:
Mwww/blog/index.txt | 1+
Awww/blog/wireguard-management.txt | 261+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 262 insertions(+), 0 deletions(-)

diff --git a/www/blog/index.txt b/www/blog/index.txt @@ -12,6 +12,7 @@ For an up to date list of software/hardware I use, see ## 2022 +- 06/22 [Automating Multi-User WireGuard setup on OpenBSD](/blog/wireguard-management.html) - 05/22 [Starting a Tilde Community for Fun and the Learnings](/blog/starting-a-tilde.html) - 05/22 [Typesetting a Resume with `mandoc(1)`](/blog/mandoc-resume.html) - 04/22 [Exploring Acme, Plan 9, and `NO_COLOR`](/blog/exploring-plan9.html) diff --git a/www/blog/wireguard-management.txt b/www/blog/wireguard-management.txt @@ -0,0 +1,261 @@ +# Automating Multi-User WireGuard setup on OpenBSD + +_Published: June 13, 2022_ + +## Background + +In my previous post, I wrote about how I [started a tilde +community](/blog/starting-a-tilde.html) with my friend +[Anthony](https://anthonymorris.dev) in 2021. In this post I want +to do a deep dive into how we set up and manage our VPN. + +We knew early on that we wanted to host web services such as a +web-based IRC client and mailing list archives, so we decided to +set up a VPN to ensure that only tilde members could access these +services. + +It was pretty easy to settle on WireGuard as our VPN of choice--it +comes in base OpenBSD (added to the kernel in recent years) and has +great clients for all platforms. However, the set up can be a bit +manual, and after surveying the slew of WireGuard configuration +management tools out there, we decided it'd be a better learning +experience and more fun to write one ourselves (that's what the +tilde is all about!). + +## The Setup + +Our tilde machine is a single VM on Linode, and we have multiple +clients that need to connect to it. While developing a mesh network +like Tailscale would be ideal, we don't currently have any use case +for client->client communication; we just want to enable members +to reach the VM (and keep non-members out). + +As such, the resulting network topology mirrors a hub and spoke, +but the VM doesn't do any routing between clients--it can talk to +each of them but they can't talk to eachother without IP forwarding +enabled on the server (likewise they can't eat the VM's bandwidth +by sending external traffic through it). To a client, it's really +just an auth-wall and less of a network. + +Regardless, the tool should be usable for setups where clients do +want access to eachother--the only changes needed would be to +configure the Allowed IPs to send traffic to the other hosts down +the wg interface and set up the sysctl.conf to allow IP forwarding. + + +## Setting Up One Client + +### Technical Details + +For the purpose of this demo, we'll use 10.6.6.1 as the private IP +for the VM and 10.6.6.0/24 addresses for the clients. + +To understand how this topology is set up, a brief overview of the +"Allowed IPs" WireGuard concept is helpful. Because WireGuard is +peer to peer, there are no true clients and servers. In our case +we made a single server, but it doesn't change the fact that the +server is just a peer with N peers (clients) and the clients are +just a peer with 1 peer (the server). + +Allowed IPs are used both for outbound and inbound traffic in +WireGuard. When sending traffic outbound, the packets are routed +to the peer with the most specific matching IP range. For a client, +having a peer of 10.6.6.1/32 will route all the traffic to that +address to that peer. When receiving traffic from a peer, the Allowed +IP range is used to filter incoming traffic. So in the case of the +server, my peer (10.6.6.2) can't send back traffic pretending to +be Anthony (10.6.6.3), because we configured the server's peers to +have Allowed IPs of just their specific IP address (10.6.6.2/32). +This server-side Allowed IP is necessary to route the traffic +destined for our clients back to the right client too. + +### Configuration + +Since the server and client are all peers, the basic information +needed for each one is the same: + +1. An IP address +2. A private key and the corresponding public key + +In addition the server requires choosing a port so clients can find +it (clients will choose their own port dynamically). + +Each peer that needs to communicate with another peer requires the +public key of the other peer. So in our setup, the server is +configured to allow traffic from all the clients by specifying their +public keys and the clients require the public key of the server. + +As of OpenBSD 7.0, here's the configuration files we used (for how +to create the keys, see "Generating the Key Combo" below). + +*Note:* the [`wg(4)`](https://man.openbsd.org/wg.4) man page is a +great reference and should be referred to before copying any configs +in case they have changed. + +#### Server + +For the server, a [`hostname.if(5)`](https://man.openbsd.org/hostname.if) +file should be created (in our case `/etc/hostname.wg0` for the +`wg0` interface). + + wgkey <server private key> wgport <secret port> + inet 10.6.6.1 255.255.255.0 + wgpeer <public key 1> wgaip 10.6.6.2/32 + wgpeer <public key 2> wgaip 10.6.6.3/32 + ... + +Where `wgpeer` defines a peer's public key and the Allowed IPs +for that peer are specified by `wgaip`. + +Once created the interface can be brought up with the following: + + # sh /etc/netstart + +Make sure to `chmod 600` and `chown root:wheel` that file! The +private key for the server is.. uh private. + +#### Client + +The client config file looks like so: + + [Interface] + PrivateKey = <private> + Address = 10.6.6.2/24 + + [Peer] + PublicKey = <public key of server> + AllowedIPs = 10.6.6.1/32 + Endpoint = <server-ip>:<secret-port> + +The config file can be used with `wg-quick` on the client: + + # wg-quick up client.conf + +Again notice that only traffic destined for the server will be +routed differently. Normal internet traffic will be sent through +the default interface. + +## Creating a Config Management Tool + +With our tool, which we called `wggen(1)`, we wanted to focus on +easing the maintenance burden more so than the initial setup. While +we only have a small handful of users (a couple more since I last +wrote!), we knew we'd need some key management to make creating new +users (and new secondary clients for existing members) easy. + +Looking at the setup, the things that need to be done are: + +1. Finding the next available IP address on the private network +2. Creating a public/private key combo +3. Updating the server `hostname.if` file to accept traffic from the public key +4. Generating a config file for the client +5. Sending the member their config file + +### Storing the Credentials + +For each client, we create a directory `/etc/wg/<client>` to store +the client's keys and configuration file. + +As a one time setup, the `/etc/wg` directory should be created with +permissions set to only give the root user access: + + # mkdir /etc/wg + # chmod 700 /etc/sg + # chown root:wheel /etc/wg + +### Finding an IP Address + +Given that we expect a small number of these, a simple solution +here was to register the hosts and their IP addresses in a flat +text file (managed by the tool). + +This file, `/etc/wg/hosts`, looks like so: + + server 10.6.6.1 + alex 10.6.6.2 + anthony 10.6.6.3 + ... + +To find the next available IP, we make use of the fact that the +file is sorted and grab the last line using `tail(1)` to see the +most recently used IP. From that, we get the last digit of that +line by using `cut(1)` splitting on the `.` separator. That number +is all we need to determine the next IP allocated. + + NAME="$1" + DATADIR=${DATADIR:-/etc/wg} + HOSTFILE=${HOSTFILE:-${DATADIR}/hosts} + + CUR=$(tail -n 1 "$HOSTFILE" | cut -d. -f 4) + NEXT=$((CUR + 1)) + +Saving the selection back is as easy as appending: + + echo "$NAME 10.6.6.$NEXT" >> "$HOSTFILE" + +### Generating the Key Combo + +The private key is generated and saved into /etc/wg/<hostname> +by using the following `openssl` oneliner (from `wg(4)`): + + CONF="$DATADIR/$NAME" + mkdir -p "$CONF" + openssl rand -base64 32 > "$CONF/private.key" + +Obtaining the public key could use the `wg(1)` tool, but +to prevent the need to install `wg-tools`, we used the clever +_"create a temporary interface and grab the public key from that"_ +trick from `wg(4)`: + + ifconfig wg9 destroy 2>/dev/null || true + ifconfig wg9 create wgport 13421 wgkey "$(cat "$CONF/private.key")" + ifconfig wg9 | grep wgpubkey | cut -d ' ' -f 2 > "$CONF/public.key" + ifconfig wg9 destroy 2>/dev/null || true + +### Generating the Config + +Generating the config is straightforward. Just a heredoc multi-line +comment (with the server-specific bits hardcoded but left out for +the sake of publishing). + + + cat <<EOM > "$CONF/client.conf" + # public key: $(cat "$CONF/public.key") + [Interface] + PrivateKey = $(cat "$CONF/private.key") + Address = 10.6.6.$NEXT/24 + + [Peer] + PublicKey = <server-public-key> + AllowedIPs = 10.6.6.1/32 + Endpoint = <server-ip>:<server-port> + EOM + +### Updating the Server's Known Peers + +To update the known peers, we update the existing server config +file by appending the public key and allowed IP followed by a +restart of the interface: + + cat <<EOM >> /etc/hostname.wg0 + wgpeer $(cat "$CONF/public.key") wgaip 10.6.6.$NEXT/32 + EOM + + sh /etc/netstart + +### Sending the Config + +Sending the config is easy--we already have email on the +[machine!](https://garbash.com/~alex/notes/004-mail-server.html) +Using the `mail(1)` client to deliver internally is a oneliner: + + mail -s "Your wireguard info" "$USERNAME" < "/etc/wg/$USERNAME/client.conf" + +## Conclusion + +Prior to writing `wggen(1)`, I'd set up WireGuard a few times on +my own mostly to learn the technology. The tilde was the perfect +excuse to solidify that knowledge and create something useful! + +As with all our little tools that came out of the tilde, the source code +is FOSS and available [here](https://git.garbash.com/alex/config/file/usr/local/bin/wggen.html).