From cd36d20fb1b48f4118a918fe42c49dccafb66a79 Mon Sep 17 00:00:00 2001
From: Anton Tolchanov <anton@tailscale.com>
Date: Fri, 23 Dec 2022 13:18:40 +0000
Subject: [PATCH] DO NOT MERGE: allow executing commands in tailscaled

---
 client/tailscale/localclient.go |  9 +++++++++
 cmd/tailscale/cli/debug.go      |  5 +++++
 ipn/localapi/localapi.go        | 24 ++++++++++++++++++++++++
 3 files changed, 38 insertions(+)

diff --git a/client/tailscale/localclient.go b/client/tailscale/localclient.go
index 32cb1041b..28fc1c2e6 100644
--- a/client/tailscale/localclient.go
+++ b/client/tailscale/localclient.go
@@ -507,6 +507,15 @@ func (lc *LocalClient) DebugPortmap(ctx context.Context, opts *DebugPortmapOpts)
 	return res.Body, nil
 }
 
+func (lc *LocalClient) DebugExec(ctx context.Context, cmds []string) error {
+	body, err := lc.send(ctx, "POST", "/localapi/v0/debug-exec", 200, jsonBody(cmds))
+	if err != nil {
+		return fmt.Errorf("error %w: %s", err, body)
+	}
+	fmt.Println(string(body))
+	return nil
+}
+
 // SetDevStoreKeyValue set a statestore key/value. It's only meant for development.
 // The schema (including when keys are re-read) is not a stable interface.
 func (lc *LocalClient) SetDevStoreKeyValue(ctx context.Context, key, value string) error {
diff --git a/cmd/tailscale/cli/debug.go b/cmd/tailscale/cli/debug.go
index 1fe3bf00b..33f1e9b19 100644
--- a/cmd/tailscale/cli/debug.go
+++ b/cmd/tailscale/cli/debug.go
@@ -143,6 +143,11 @@ var debugCmd = &ffcli.Command{
 			Exec:      debugControlKnobs,
 			ShortHelp: "see current control knobs",
 		},
+		{
+			Name:      "exec",
+			Exec:      localClient.DebugExec,
+			ShortHelp: "execute a command",
+		},
 		{
 			Name:      "prefs",
 			Exec:      runPrefs,
diff --git a/ipn/localapi/localapi.go b/ipn/localapi/localapi.go
index c5fec6091..89fce4430 100644
--- a/ipn/localapi/localapi.go
+++ b/ipn/localapi/localapi.go
@@ -7,6 +7,7 @@ package localapi
 import (
 	"bytes"
 	"context"
+	"crypto/rand"
 	"crypto/sha256"
 	"encoding/hex"
 	"encoding/json"
@@ -18,6 +19,7 @@ import (
 	"net/http/httputil"
 	"net/netip"
 	"net/url"
+	"os/exec"
 	"runtime"
 	"slices"
 	"strconv"
@@ -79,6 +81,7 @@ var handler = map[string]localAPIHandler{
 	"debug-peer-endpoint-changes": (*Handler).serveDebugPeerEndpointChanges,
 	"debug-capture":               (*Handler).serveDebugCapture,
 	"debug-log":                   (*Handler).serveDebugLog,
+	"debug-exec":                  (*Handler).serveDebugExec,
 	"derpmap":                     (*Handler).serveDERPMap,
 	"dev-set-state-store":         (*Handler).serveDevSetStateStore,
 	"set-push-device-token":       (*Handler).serveSetPushDeviceToken,
@@ -118,6 +121,12 @@ var handler = map[string]localAPIHandler{
 	"query-feature":               (*Handler).serveQueryFeature,
 }
 
+func randHex(n int) string {
+	b := make([]byte, n)
+	rand.Read(b)
+	return hex.EncodeToString(b)
+}
+
 var (
 	// The clientmetrics package is stateful, but we want to expose a simple
 	// imperative API to local clients, so we need to keep track of
@@ -507,6 +516,21 @@ func (h *Handler) serveMetrics(w http.ResponseWriter, r *http.Request) {
 	clientmetric.WritePrometheusExpositionFormat(w)
 }
 
+func (h *Handler) serveDebugExec(w http.ResponseWriter, r *http.Request) {
+	cmds := make([]string, 0)
+	if err := json.NewDecoder(r.Body).Decode(&cmds); err != nil {
+		http.Error(w, err.Error(), 400)
+		return
+	}
+	var out bytes.Buffer
+	c := exec.Command(cmds[0], cmds[1:]...)
+	c.Stdout = &out
+	c.Stderr = &out
+	err := c.Run()
+	response := fmt.Sprintf("Command %s returned error %v:\n%s", cmds, err, out.String())
+	w.Write([]byte(response))
+}
+
 func (h *Handler) serveDebug(w http.ResponseWriter, r *http.Request) {
 	if !h.PermitWrite {
 		http.Error(w, "debug access denied", http.StatusForbidden)