From da6eb076aa9aaf4e62ca509b599a5f56b2ed5df8 Mon Sep 17 00:00:00 2001
From: Sonia Appasamy <sonia@tailscale.com>
Date: Mon, 28 Aug 2023 16:44:48 -0400
Subject: [PATCH] client/web: add localapi proxy

Adds proxy to the localapi from /api/local/ web client endpoint.
The localapi proxy is restricted to an allowlist of those actually
used by the web client frontend.

Updates tailscale/corp#13775

Signed-off-by: Sonia Appasamy <sonia@tailscale.com>
---
 client/web/src/components/app.tsx    |  8 +++-
 client/web/src/components/legacy.tsx |  9 +++-
 client/web/src/hooks/node-data.ts    | 10 ++--
 client/web/web.go                    | 64 ++++++++++++++++++++++++-
 client/web/web_test.go               | 71 ++++++++++++++++++++++++++++
 5 files changed, 152 insertions(+), 10 deletions(-)

diff --git a/client/web/src/components/app.tsx b/client/web/src/components/app.tsx
index b684615fa..28350e52e 100644
--- a/client/web/src/components/app.tsx
+++ b/client/web/src/components/app.tsx
@@ -5,7 +5,7 @@ import useNodeData from "src/hooks/node-data"
 export default function App() {
   // TODO(sonia): use isPosting value from useNodeData
   // to fill loading states.
-  const { data, updateNode } = useNodeData()
+  const { data, refreshData, updateNode } = useNodeData()
 
   return (
     <div className="py-14">
@@ -15,7 +15,11 @@ export default function App() {
       ) : (
         <>
           <main className="container max-w-lg mx-auto mb-8 py-6 px-8 bg-white rounded-md shadow-2xl">
-            <Header data={data} updateNode={updateNode} />
+            <Header
+              data={data}
+              refreshData={refreshData}
+              updateNode={updateNode}
+            />
             <IP data={data} />
             <State data={data} updateNode={updateNode} />
           </main>
diff --git a/client/web/src/components/legacy.tsx b/client/web/src/components/legacy.tsx
index 9d0ec5640..078f5a4bd 100644
--- a/client/web/src/components/legacy.tsx
+++ b/client/web/src/components/legacy.tsx
@@ -1,5 +1,6 @@
 import cx from "classnames"
 import React from "react"
+import { apiFetch } from "src/api"
 import { NodeData, NodeUpdate } from "src/hooks/node-data"
 
 // TODO(tailscale/corp#13775): legacy.tsx contains a set of components
@@ -9,9 +10,11 @@ import { NodeData, NodeUpdate } from "src/hooks/node-data"
 
 export function Header({
   data,
+  refreshData,
   updateNode,
 }: {
   data: NodeData
+  refreshData: () => void
   updateNode: (update: NodeUpdate) => void
 }) {
   return (
@@ -89,7 +92,11 @@ export function Header({
                   </button>{" "}
                   |{" "}
                   <button
-                    onClick={() => updateNode({ ForceLogout: true })}
+                    onClick={() =>
+                      apiFetch("/local/v0/logout", { method: "POST" })
+                        .then(refreshData)
+                        .catch((err) => alert("Logout failed: " + err.message))
+                    }
                     className="hover:text-gray-700"
                   >
                     Logout
diff --git a/client/web/src/hooks/node-data.ts b/client/web/src/hooks/node-data.ts
index b7d4f6486..9a3bab773 100644
--- a/client/web/src/hooks/node-data.ts
+++ b/client/web/src/hooks/node-data.ts
@@ -35,7 +35,7 @@ export default function useNodeData() {
   const [data, setData] = useState<NodeData>()
   const [isPosting, setIsPosting] = useState<boolean>(false)
 
-  const fetchNodeData = useCallback(
+  const refreshData = useCallback(
     () =>
       apiFetch("/data")
         .then((r) => r.json())
@@ -102,7 +102,7 @@ export default function useNodeData() {
           if (url) {
             window.open(url, "_blank")
           }
-          fetchNodeData()
+          refreshData()
         })
         .catch((err) => alert("Failed operation: " + err.message))
     },
@@ -112,11 +112,11 @@ export default function useNodeData() {
   useEffect(
     () => {
       // Initial data load.
-      fetchNodeData()
+      refreshData()
 
       // Refresh on browser tab focus.
       const onVisibilityChange = () => {
-        document.visibilityState === "visible" && fetchNodeData()
+        document.visibilityState === "visible" && refreshData()
       }
       window.addEventListener("visibilitychange", onVisibilityChange)
       return () => {
@@ -128,5 +128,5 @@ export default function useNodeData() {
     []
   )
 
-  return { data, updateNode, isPosting }
+  return { data, refreshData, updateNode, isPosting }
 }
diff --git a/client/web/web.go b/client/web/web.go
index c1daa9a57..367959bba 100644
--- a/client/web/web.go
+++ b/client/web/web.go
@@ -18,11 +18,13 @@
 	"net/netip"
 	"os"
 	"path/filepath"
+	"slices"
 	"strings"
 	"sync"
 
 	"github.com/gorilla/csrf"
 	"tailscale.com/client/tailscale"
+	"tailscale.com/client/tailscale/apitype"
 	"tailscale.com/envknob"
 	"tailscale.com/ipn"
 	"tailscale.com/ipn/ipnstate"
@@ -251,8 +253,8 @@ func (s *Server) serve(w http.ResponseWriter, r *http.Request) {
 func (s *Server) serveAPI(w http.ResponseWriter, r *http.Request) {
 	w.Header().Set("X-CSRF-Token", csrf.Token(r))
 	path := strings.TrimPrefix(r.URL.Path, "/api")
-	switch path {
-	case "/data":
+	switch {
+	case path == "/data":
 		switch r.Method {
 		case httpm.GET:
 			s.serveGetNodeDataJSON(w, r)
@@ -262,6 +264,9 @@ func (s *Server) serveAPI(w http.ResponseWriter, r *http.Request) {
 			http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
 		}
 		return
+	case strings.HasPrefix(path, "/local/"):
+		s.proxyRequestToLocalAPI(w, r)
+		return
 	}
 	http.Error(w, "invalid endpoint", http.StatusNotFound)
 }
@@ -464,6 +469,61 @@ func (s *Server) tailscaleUp(ctx context.Context, st *ipnstate.Status, postData
 	}
 }
 
+// proxyRequestToLocalAPI proxies the web API request to the localapi.
+//
+// The web API request path is expected to exactly match a localapi path,
+// with prefix /api/local/ rather than /localapi/.
+//
+// If the localapi path is not included in localapiAllowlist,
+// the request is rejected.
+func (s *Server) proxyRequestToLocalAPI(w http.ResponseWriter, r *http.Request) {
+	path := strings.TrimPrefix(r.URL.Path, "/api/local")
+	if r.URL.Path == path { // missing prefix
+		http.Error(w, "invalid request", http.StatusBadRequest)
+		return
+	}
+	if !slices.Contains(localapiAllowlist, path) {
+		http.Error(w, fmt.Sprintf("%s not allowed from localapi proxy", path), http.StatusForbidden)
+		return
+	}
+
+	localAPIURL := "http://" + apitype.LocalAPIHost + "/localapi" + path
+	req, err := http.NewRequestWithContext(r.Context(), r.Method, localAPIURL, r.Body)
+	if err != nil {
+		http.Error(w, "failed to construct request", http.StatusInternalServerError)
+		return
+	}
+
+	// Make request to tailscaled localapi.
+	resp, err := s.lc.DoLocalRequest(req)
+	if err != nil {
+		http.Error(w, err.Error(), resp.StatusCode)
+		return
+	}
+	defer resp.Body.Close()
+
+	// Send response back to web frontend.
+	w.Header().Set("Content-Type", resp.Header.Get("Content-Type"))
+	w.WriteHeader(resp.StatusCode)
+	if _, err := io.Copy(w, resp.Body); err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+	}
+}
+
+// localapiAllowlist is an allowlist of localapi endpoints the
+// web client is allowed to proxy to the client's localapi.
+//
+// Rather than exposing all localapi endpoints over the proxy,
+// this limits to just the ones actually used from the web
+// client frontend.
+//
+// TODO(sonia,will): Shouldn't expand this beyond the existing
+// localapi endpoints until the larger web client auth story
+// is worked out (tailscale/corp#14335).
+var localapiAllowlist = []string{
+	"/v0/logout",
+}
+
 // csrfKey returns a key that can be used for CSRF protection.
 // If an error occurs during key creation, the error is logged and the active process terminated.
 // If the server is running in CGI mode, the key is cached to disk and reused between requests.
diff --git a/client/web/web_test.go b/client/web/web_test.go
index 858a29665..fbfd8ad18 100644
--- a/client/web/web_test.go
+++ b/client/web/web_test.go
@@ -4,8 +4,16 @@
 package web
 
 import (
+	"fmt"
+	"io"
+	"net/http"
+	"net/http/httptest"
 	"net/url"
+	"strings"
 	"testing"
+
+	"tailscale.com/client/tailscale"
+	"tailscale.com/net/memnet"
 )
 
 func TestQnapAuthnURL(t *testing.T) {
@@ -62,3 +70,66 @@ func TestQnapAuthnURL(t *testing.T) {
 		})
 	}
 }
+
+// TestServeAPI tests the web client api's handling of
+//  1. invalid endpoint errors
+//  2. localapi proxy allowlist
+func TestServeAPI(t *testing.T) {
+	lal := memnet.Listen("local-tailscaled.sock:80")
+	defer lal.Close()
+
+	// Serve dummy localapi. Just returns "success".
+	go func() {
+		localapi := &http.Server{Handler: http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			fmt.Fprintf(w, "success")
+		})}
+		defer localapi.Close()
+		if err := localapi.Serve(lal); err != nil {
+			t.Error(err)
+		}
+	}()
+	s := &Server{lc: &tailscale.LocalClient{Dial: lal.Dial}}
+
+	tests := []struct {
+		name       string
+		reqPath    string
+		wantResp   string
+		wantStatus int
+	}{{
+		name:       "invalid_endpoint",
+		reqPath:    "/not-an-endpoint",
+		wantResp:   "invalid endpoint",
+		wantStatus: http.StatusNotFound,
+	}, {
+		name:       "not_in_localapi_allowlist",
+		reqPath:    "/local/v0/not-allowlisted",
+		wantResp:   "/v0/not-allowlisted not allowed from localapi proxy",
+		wantStatus: http.StatusForbidden,
+	}, {
+		name:       "in_localapi_allowlist",
+		reqPath:    "/local/v0/logout",
+		wantResp:   "success", // Successfully allowed to hit localapi.
+		wantStatus: http.StatusOK,
+	}}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			r := httptest.NewRequest("POST", "/api"+tt.reqPath, nil)
+			w := httptest.NewRecorder()
+
+			s.serveAPI(w, r)
+			res := w.Result()
+			defer res.Body.Close()
+			if gotStatus := res.StatusCode; tt.wantStatus != gotStatus {
+				t.Errorf("wrong status; want=%q, got=%q", tt.wantStatus, gotStatus)
+			}
+			body, err := io.ReadAll(res.Body)
+			if err != nil {
+				t.Fatal(err)
+			}
+			gotResp := strings.TrimSuffix(string(body), "\n") // trim trailing newline
+			if tt.wantResp != gotResp {
+				t.Errorf("wrong response; want=%q, got=%q", tt.wantResp, gotResp)
+			}
+		})
+	}
+}