Brad FitzpatrickandBrad Fitzpatrick
c1ae2bb1f8
Add a new Prefs.RemoteConfig bool. When true, a c2n endpoint at
/remoteapi/localapi/* proxies into this node's LocalAPI at
/localapi/* with full read/write permission, giving the tailnet
admin the same API surface a local root/admin user has via the
tailscale CLI. All LocalAPI versions (v0, v1, ...) proxy through.
RemoteConfig is an alternative to Tailscale's default per-feature
double opt-in, in which both the tailnet admin and the local machine
owner must consent to each individual setting change. It is a single
client-side "I trust the tailnet admin" switch that, once on, hands
over full remote management of this node's settings and LocalAPI
without any further local prompt or confirmation.
This is only appropriate when the tailnet admin already owns the
machine (e.g. a corporate fleet device) or the local user has
explicitly delegated full control. It should never be enabled on a
personal/BYOD device with an untrusted tailnet admin. The trust
model is documented on the pref, on the hidden --remote-config CLI
flag, and on the feature/remoteconfig package.
The node advertises its RemoteConfig state to the control plane via
a new Hostinfo.RemoteConfig bool. This is only true when the feature
is both compiled in (buildfeatures.HasRemoteConfig) and its init
actually ran (feature.IsRegistered("remoteconfig")); tsnet builds
have the former but not the latter and correctly report false.
The handler lives in feature/remoteconfig and can be omitted with the
ts_omit_remoteconfig build tag. tsnet's TestDeps guards against
accidentally pulling it in.
Updates tailscale/corp#18043
Change-Id: I72ce10a90a0e4e738c72c940af3af64c986160b2
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
95 lines
3.2 KiB
Go
95 lines
3.2 KiB
Go
// Copyright (c) Tailscale Inc & contributors
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// SPDX-License-Identifier: BSD-3-Clause
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// Package remoteconfig registers a c2n endpoint that lets the control
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// plane invoke this node's LocalAPI when Prefs.RemoteConfig is true.
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//
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// # Trust model
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//
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// Tailscale's default posture is per-feature double opt-in: the tailnet
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// admin can request something server-side, but the local machine owner
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// still has to consent (via CLI, GUI, or LocalAPI) for each individual
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// setting. RemoteConfig is a different, more permissive posture: a
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// single client-side "I trust the tailnet admin" switch. Once
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// Prefs.RemoteConfig is true, the control plane can invoke any of this
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// node's LocalAPI endpoints (which includes read/write of every pref)
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// with no further local consent.
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//
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// This is appropriate when the tailnet admin owns the machine (e.g. a
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// corporate fleet device) or when the local user has explicitly
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// delegated full control to the tailnet admin. It should NOT be used
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// on personal or BYOD devices where the tailnet admin is not fully
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// trusted.
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package remoteconfig
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import (
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"net/http"
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"strings"
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"tailscale.com/feature"
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"tailscale.com/ipn/ipnauth"
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"tailscale.com/ipn/ipnlocal"
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"tailscale.com/ipn/localapi"
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)
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// c2nPrefix is the c2n URL path prefix under which requests are
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// proxied to this node's LocalAPI at /localapi/*, regardless of the
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// LocalAPI version (v0, v1, ...).
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const c2nPrefix = "/remoteapi/localapi/"
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// localAPIStrip is the portion of c2nPrefix that must be stripped from
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// the incoming c2n path to yield the LocalAPI path.
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const localAPIStrip = "/remoteapi"
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func init() {
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feature.Register("remoteconfig")
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ipnlocal.RegisterC2NPrefix(c2nPrefix, handleC2NRemoteAPI)
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}
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// handleC2NRemoteAPI proxies c2n requests under /remoteapi/localapi/*
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// to this node's LocalAPI at /localapi/*, with full read/write
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// permission, when the local machine has opted in via Prefs.RemoteConfig.
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//
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// See the package doc for the trust model this handler represents.
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func handleC2NRemoteAPI(b *ipnlocal.LocalBackend, w http.ResponseWriter, r *http.Request) {
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prefs := b.Prefs()
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if !prefs.Valid() || !prefs.RemoteConfig() {
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http.Error(w, "remote config not enabled by local machine", http.StatusForbidden)
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return
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}
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if !strings.HasPrefix(r.URL.Path, c2nPrefix) {
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http.Error(w, "unexpected remote-config path", http.StatusBadRequest)
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return
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}
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// Rewrite the URL from /remoteapi/localapi/X to /localapi/X on a
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// shallow clone so we don't mutate the caller's Request.
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u := *r.URL
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u.Path = strings.TrimPrefix(r.URL.Path, localAPIStrip)
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if r.URL.RawPath != "" {
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u.RawPath = strings.TrimPrefix(r.URL.RawPath, localAPIStrip)
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}
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r2 := r.WithContext(r.Context())
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r2.URL = &u
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if u.Path == r.URL.Path {
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// Prefix strip did nothing; refuse rather than looping.
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http.Error(w, "unexpected remote-config path", http.StatusBadRequest)
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return
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}
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if !strings.HasPrefix(u.Path, "/localapi/") {
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http.Error(w, "unexpected remote-config path", http.StatusBadRequest)
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return
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}
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lah := localapi.NewHandler(localapi.HandlerConfig{
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Actor: ipnauth.Self,
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Backend: b,
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Logf: b.Logger(),
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LogID: b.BackendLogID(),
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EventBus: b.Sys().Bus.Get(),
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})
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lah.PermitRead = true
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lah.PermitWrite = true
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lah.ServeHTTP(w, r2)
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}
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