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Merge pull request #311 from restanrm/docs-acl-modifications
Issues with current ACL implementation and solution proposal
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Kristoffer Dalby
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docs/proposals/001-acls.md
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docs/proposals/001-acls.md
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# ACLs
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A key component of tailscale is the notion of Tailnet. This notion is hidden
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but the implications that it have on how to use tailscale are not.
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For tailscale an [tailnet](https://tailscale.com/kb/1136/tailnet/) is the
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following:
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> For personal users, you are a tailnet of many devices and one person. Each
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> device gets a private Tailscale IP address in the CGNAT range and every
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> device can talk directly to every other device, wherever they are on the
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> internet.
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>
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> For businesses and organizations, a tailnet is many devices and many users.
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> It can be based on your Microsoft Active Directory, your Google Workspace, a
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> GitHub organization, Okta tenancy, or other identity provider namespace. All
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> of the devices and users in your tailnet can be seen by the tailnet
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> administrators in the Tailscale admin console. There you can apply
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> tailnet-wide configuration, such as ACLs that affect visibility of devices
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> inside your tailnet, DNS settings, and more.
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## Current implementation and issues
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Currently in headscale, the namespaces are used both as tailnet and users. The
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issue is that if we want to use the ACL's we can't use both at the same time.
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Tailnet's cannot communicate with each others. So we can't have an ACL that
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authorize tailnet (namespace) A to talk to tailnet (namespace) B.
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We also can't write ACLs based on the users (namespaces in headscale) since all
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devices belong to the same user.
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With the current implementation the only ACL that we can user is to associate
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each headscale IP to a host manually then write the ACLs according to this
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manual mapping.
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```json
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{
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"hosts": {
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"host1": "100.64.0.1",
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"server": "100.64.0.2"
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},
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"acls": [
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{ "action": "accept", "users": ["host1"], "ports": ["host2:80,443"] }
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]
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}
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```
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While this works, it requires a lot of manual editing on the configuration and
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to keep track of all devices IP address.
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## Proposition for a next implementation
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In order to ease the use of ACL's we need to split the tailnet and users
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notion.
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A solution could be to consider a headscale server (in it's entirety) as a
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tailnet.
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For personal users the default behavior could either allow all communications
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between all namespaces (like tailscale) or dissallow all communications between
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namespaces (current behavior).
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For businesses and organisations, viewing a headscale instance a single tailnet
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would allow users (namespace) to talk to each other with the ACLs. As described
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in tailscale's documentation [[1]], a server should be tagged and personnal
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devices should be tied to a user. Translated in headscale's terms each user can
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have multiple devices and all those devices should be in the same namespace.
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The servers should be tagged and used as such.
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This implementation would render useless the sharing feature that is currently
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implemented since an ACL could do the same. Simplifying to only one user
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interface to do one thing is easier and less confusing for the users.
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To better suit the ACLs in this proposition, it's advised to consider that each
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namespaces belong to one person. This person can have multiple devices, they
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will all be considered as the same user in the ACLs. OIDC feature wouldn't need
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to map people to namespace, just create a namespace if the person isn't
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registered yet.
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As a sidenote, users would like to write ACLs as YAML. We should offer users
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the ability to rules in either format (HuJSON or YAML).
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[1]: https://tailscale.com/kb/1068/acl-tags/
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## Example
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Let's build an example use case for a small business (It may be the place where
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ACL's are the most useful).
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We have a small company with a boss, an admin, two developper and an intern.
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The boss should have access to all servers but not to the users hosts. Admin
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should also have access to all hosts except that their permissions should be
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limited to maintaining the hosts (for example purposes). The developers can do
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anything they want on dev hosts, but only watch on productions hosts. Intern
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can only interact with the development servers.
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Each user have at least a device connected to the network and we have some
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servers.
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- database.prod
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- database.dev
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- app-server1.prod
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- app-server1.dev
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- billing.internal
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### Current headscale implementation
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Let's create some namespaces
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```bash
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headscale namespaces create prod
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headscale namespaces create dev
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headscale namespaces create internal
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headscale namespaces create users
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headscale nodes register -n users boss-computer
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headscale nodes register -n users admin1-computer
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headscale nodes register -n users dev1-computer
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headscale nodes register -n users dev1-phone
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headscale nodes register -n users dev2-computer
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headscale nodes register -n users intern1-computer
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headscale nodes register -n prod database
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headscale nodes register -n prod app-server1
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headscale nodes register -n dev database
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headscale nodes register -n dev app-server1
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headscale nodes register -n internal billing
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headscale nodes list
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ID | Name | Namespace | IP address
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1 | boss-computer | users | 100.64.0.1
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2 | admin1-computer | users | 100.64.0.2
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3 | dev1-computer | users | 100.64.0.3
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4 | dev1-phone | users | 100.64.0.4
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5 | dev2-computer | users | 100.64.0.5
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6 | intern1-computer | users | 100.64.0.6
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7 | database | prod | 100.64.0.7
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8 | app-server1 | prod | 100.64.0.8
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9 | database | dev | 100.64.0.9
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10 | app-server1 | dev | 100.64.0.10
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11 | internal | internal | 100.64.0.11
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```
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In order to only allow the communications related to our description above we
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need to add the following ACLs
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```json
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{
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"hosts": {
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"boss-computer": "100.64.0.1",
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"admin1-computer": "100.64.0.2",
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"dev1-computer": "100.64.0.3",
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"dev1-phone": "100.64.0.4",
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"dev2-computer": "100.64.0.5",
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"intern1-computer": "100.64.0.6",
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"prod-app-server1": "100.64.0.8"
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},
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"groups": {
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"group:dev": ["dev1-computer", "dev1-phone", "dev2-computer"],
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"group:admin": ["admin1-computer"],
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"group:boss": ["boss-computer"],
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"group:intern": ["intern1-computer"]
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},
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"acls": [
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// boss have access to all servers but no users hosts
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{
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"action": "accept",
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"users": ["group:boss"],
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"ports": ["prod:*", "dev:*", "internal:*"]
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},
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// admin have access to adminstration port (lets only consider port 22 here)
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{
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"action": "accept",
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"users": ["group:admin"],
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"ports": ["prod:22", "dev:22", "internal:22"]
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},
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// dev can do anything on dev servers and check access on prod servers
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{
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"action": "accept",
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"users": ["group:dev"],
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"ports": ["dev:*", "prod-app-server1:80,443"]
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},
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// interns only have access to port 80 and 443 on dev servers (lame internship)
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{ "action": "accept", "users": ["group:intern"], "ports": ["dev:80,443"] },
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// users can access their own devices
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{
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"action": "accept",
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"users": ["dev1-computer"],
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"ports": ["dev1-phone:*"]
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},
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{
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"action": "accept",
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"users": ["dev1-phone"],
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"ports": ["dev1-computer:*"]
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},
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// internal namespace communications should still be allowed within the namespace
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{ "action": "accept", "users": ["dev"], "ports": ["dev:*"] },
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{ "action": "accept", "users": ["prod"], "ports": ["prod:*"] },
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{ "action": "accept", "users": ["internal"], "ports": ["internal:*"] }
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]
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}
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```
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Since communications between namespace isn't possible we also have to share the
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devices between the namespaces.
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```bash
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// add boss host to prod, dev and internal network
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headscale nodes share -i 1 -n prod
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headscale nodes share -i 1 -n dev
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headscale nodes share -i 1 -n internal
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// add admin computer to prod, dev and internal network
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headscale nodes share -i 2 -n prod
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headscale nodes share -i 2 -n dev
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headscale nodes share -i 2 -n internal
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// add all dev to prod and dev network
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headscale nodes share -i 3 -n dev
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headscale nodes share -i 4 -n dev
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headscale nodes share -i 3 -n prod
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headscale nodes share -i 4 -n prod
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headscale nodes share -i 5 -n dev
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headscale nodes share -i 5 -n prod
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headscale nodes share -i 6 -n dev
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```
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This fake network have not been tested but it should work. Operating it could
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be quite tedious if the company grows. Each time a new user join we have to add
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it to a group, and share it to the correct namespaces. If the user want
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multiple devices we have to allow communication to each of them one by one. If
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business conduct a change in the organisations we may have to rewrite all acls
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and reorganise all namespaces.
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If we add servers in production we should also update the ACLs to allow dev
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access to certain category of them (only app servers for example).
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### example based on the proposition in this document
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Let's create the namespaces
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```bash
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headscale namespaces create boss
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headscale namespaces create admin1
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headscale namespaces create dev1
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headscale namespaces create dev2
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headscale namespaces create intern1
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```
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We don't need to create namespaces for the servers because the servers will be
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tagged. When registering the servers we will need to add the flag
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`--advertised-tags=tag:<tag1>,tag:<tag2>`, and the user (namespace) that is
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registering the server should be allowed to do it. Since anyone can add tags to
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a server they can register, the check of the tags is done on headscale server
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and only valid tags are applied. A tag is valid if the namespace that is
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registering it is allowed to do it.
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Here are the ACL's to implement the same permissions as above:
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```json
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{
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// groups are simpler and only list the namespaces name
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"groups": {
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"group:boss": ["boss"],
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"group:dev": ["dev1", "dev2"],
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"group:admin": ["admin1"],
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"group:intern": ["intern1"]
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},
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"tagOwners": {
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// the administrators can add servers in production
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"tag:prod-databases": ["group:admin"],
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"tag:prod-app-servers": ["group:admin"],
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// the boss can tag any server as internal
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"tag:internal": ["group:boss"],
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// dev can add servers for dev purposes as well as admins
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"tag:dev-databases": ["group:admin", "group:dev"],
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"tag:dev-app-servers": ["group:admin", "group:dev"]
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// interns cannot add servers
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},
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"acls": [
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// boss have access to all servers
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{
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"action": "accept",
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"users": ["group:boss"],
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"ports": [
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"tag:prod-databases:*",
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"tag:prod-app-servers:*",
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"tag:internal:*",
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"tag:dev-databases:*",
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"tag:dev-app-servers:*"
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]
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},
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// admin have only access to administrative ports of the servers
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{
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"action": "accept",
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"users": ["group:admin"],
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"ports": [
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"tag:prod-databases:22",
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"tag:prod-app-servers:22",
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"tag:internal:22",
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"tag:dev-databases:22",
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"tag:dev-app-servers:22"
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]
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},
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{
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"action": "accept",
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"users": ["group:dev"],
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"ports": [
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"tag:dev-databases:*",
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"tag:dev-app-servers:*",
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"tag:prod-app-servers:80,443"
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]
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},
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// servers should be able to talk to database. Database should not be able to initiate connections to server
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{
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"action": "accept",
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"users": ["tag:dev-app-servers"],
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"ports": ["tag:dev-databases:5432"]
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},
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{
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"action": "accept",
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"users": ["tag:prod-app-servers"],
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"ports": ["tag:prod-databases:5432"]
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},
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// interns have access to dev-app-servers only in reading mode
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{
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"action": "accept",
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"users": ["group:intern"],
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"ports": ["tag:dev-app-servers:80,443"]
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},
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// we still have to allow internal namespaces communications since nothing guarantees that each user have their own namespaces. This could be talked over.
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{ "action": "accept", "users": ["boss"], "ports": ["boss:*"] },
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{ "action": "accept", "users": ["dev1"], "ports": ["dev1:*"] },
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{ "action": "accept", "users": ["dev2"], "ports": ["dev2:*"] },
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{ "action": "accept", "users": ["admin1"], "ports": ["admin1:*"] },
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{ "action": "accept", "users": ["intern1"], "ports": ["intern1:*"] }
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]
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}
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```
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With this implementation, the sharing step is not necessary. Maintenance cost
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of the ACL file is lower and less tedious (no need to map hostname and IP's
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into it).
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