cmd/puppeth, vendor: update ssh, manage server keys (#14398)

Author: karalabe

cmd/puppeth/ssh.go

@@ -17,6 +17,8 @@
 package main
 
 import (
+	"bufio"
+	"bytes"
 	"errors"
 	"fmt"
 	"io/ioutil"
@@ -37,25 +39,36 @@ import (
 type sshClient struct {
 	server  string // Server name or IP without port number
 	address string // IP address of the remote server
+	pubkey  []byte // RSA public key to authenticate the server
 	client  *ssh.Client
 	logger  log.Logger
 }
 
 // dial establishes an SSH connection to a remote node using the current user and
-// the user's configured private RSA key.
-func dial(server string) (*sshClient, error) {
+// the user's configured private RSA key. If that fails, password authentication
+// is fallen back to. The caller may override the login user via user@server:port.
+func dial(server string, pubkey []byte) (*sshClient, error) {
 	// Figure out a label for the server and a logger
 	label := server
 	if strings.Contains(label, ":") {
 		label = label[:strings.Index(label, ":")]
 	}
+	login := ""
+	if strings.Contains(server, "@") {
+		login = label[:strings.Index(label, "@")]
+		label = label[strings.Index(label, "@")+1:]
+		server = server[strings.Index(server, "@")+1:]
+	}
 	logger := log.New("server", label)
 	logger.Debug("Attempting to establish SSH connection")
 
 	user, err := user.Current()
 	if err != nil {
 		return nil, err
 	}
+	if login == "" {
+		login = user.Username
+	}
 	// Configure the supported authentication methods (private key and password)
 	var auths []ssh.AuthMethod
 
@@ -71,7 +84,7 @@ func dial(server string) (*sshClient, error) {
 		}
 	}
 	auths = append(auths, ssh.PasswordCallback(func() (string, error) {
-		fmt.Printf("What's the login password for %s at %s? (won't be echoed)\n> ", user.Username, server)
+		fmt.Printf("What's the login password for %s at %s? (won't be echoed)\n> ", login, server)
 		blob, err := terminal.ReadPassword(int(syscall.Stdin))
 
 		fmt.Println()
@@ -86,18 +99,44 @@ func dial(server string) (*sshClient, error) {
 		return nil, errors.New("no IPs associated with domain")
 	}
 	// Try to dial in to the remote server
-	logger.Trace("Dialing remote SSH server", "user", user.Username, "key", path)
+	logger.Trace("Dialing remote SSH server", "user", login)
 	if !strings.Contains(server, ":") {
 		server += ":22"
 	}
-	client, err := ssh.Dial("tcp", server, &ssh.ClientConfig{User: user.Username, Auth: auths})
+	keycheck := func(hostname string, remote net.Addr, key ssh.PublicKey) error {
+		// If no public key is known for SSH, ask the user to confirm
+		if pubkey == nil {
+			fmt.Printf("The authenticity of host '%s (%s)' can't be established.\n", hostname, remote)
+			fmt.Printf("SSH key fingerprint is %s [MD5]\n", ssh.FingerprintLegacyMD5(key))
+			fmt.Printf("Are you sure you want to continue connecting (yes/no)? ")
+
+			text, err := bufio.NewReader(os.Stdin).ReadString('\n')
+			switch {
+			case err != nil:
+				return err
+			case strings.TrimSpace(text) == "yes":
+				pubkey = key.Marshal()
+				return nil
+			default:
+				return fmt.Errorf("unknown auth choice: %v", text)
+			}
+		}
+		// If a public key exists for this SSH server, check that it matches
+		if bytes.Compare(pubkey, key.Marshal()) == 0 {
+			return nil
+		}
+		// We have a mismatch, forbid connecting
+		return errors.New("ssh key mismatch, readd the machine to update")
+	}
+	client, err := ssh.Dial("tcp", server, &ssh.ClientConfig{User: login, Auth: auths, HostKeyCallback: keycheck})
 	if err != nil {
 		return nil, err
 	}
 	// Connection established, return our utility wrapper
 	c := &sshClient{
 		server:  label,
 		address: addr[0],
+		pubkey:  pubkey,
 		client:  client,
 		logger:  logger,
 	}

cmd/puppeth/wizard.go

@@ -44,14 +44,24 @@ type config struct {
 	bootLight []string      // Bootnodes to always connect to by light nodes
 	ethstats  string        // Ethstats settings to cache for node deploys
 
-	Servers []string `json:"servers,omitempty"`
+	Servers map[string][]byte `json:"servers,omitempty"`
+}
+
+// servers retrieves an alphabetically sorted list of servers.
+func (c config) servers() []string {
+	servers := make([]string, 0, len(c.Servers))
+	for server := range c.Servers {
+		servers = append(servers, server)
+	}
+	sort.Strings(servers)
+
+	return servers
 }
 
 // flush dumps the contents of config to disk.
 func (c config) flush() {
 	os.MkdirAll(filepath.Dir(c.path), 0755)
 
-	sort.Strings(c.Servers)
 	out, _ := json.MarshalIndent(c, "", "  ")
 	if err := ioutil.WriteFile(c.path, out, 0644); err != nil {
 		log.Warn("Failed to save puppeth configs", "file", c.path, "err", err)

cmd/puppeth/wizard_intro.go

@@ -31,7 +31,10 @@ import (
 // makeWizard creates and returns a new puppeth wizard.
 func makeWizard(network string) *wizard {
 	return &wizard{
-		network:  network,
+		network: network,
+		conf: config{
+			Servers: make(map[string][]byte),
+		},
 		servers:  make(map[string]*sshClient),
 		services: make(map[string][]string),
 		in:       bufio.NewReader(os.Stdin),
@@ -77,9 +80,9 @@ func (w *wizard) run() {
 	} else if err := json.Unmarshal(blob, &w.conf); err != nil {
 		log.Crit("Previous configuration corrupted", "path", w.conf.path, "err", err)
 	} else {
-		for _, server := range w.conf.Servers {
+		for server, pubkey := range w.conf.Servers {
 			log.Info("Dialing previously configured server", "server", server)
-			client, err := dial(server)
+			client, err := dial(server, pubkey)
 			if err != nil {
 				log.Error("Previous server unreachable", "server", server, "err", err)
 			}

cmd/puppeth/wizard_netstats.go

@@ -41,14 +41,14 @@ func (w *wizard) networkStats(tips bool) {
 	stats.SetHeader([]string{"Server", "IP", "Status", "Service", "Details"})
 	stats.SetColWidth(128)
 
-	for _, server := range w.conf.Servers {
+	for server, pubkey := range w.conf.Servers {
 		client := w.servers[server]
 		logger := log.New("server", server)
 		logger.Info("Starting remote server health-check")
 
 		// If the server is not connected, try to connect again
 		if client == nil {
-			conn, err := dial(server)
+			conn, err := dial(server, pubkey)
 			if err != nil {
 				logger.Error("Failed to establish remote connection", "err", err)
 				stats.Append([]string{server, "", err.Error(), "", ""})

cmd/puppeth/wizard_network.go

@@ -28,7 +28,9 @@ import (
 func (w *wizard) manageServers() {
 	// List all the servers we can disconnect, along with an entry to connect a new one
 	fmt.Println()
-	for i, server := range w.conf.Servers {
+
+	servers := w.conf.servers()
+	for i, server := range servers {
 		fmt.Printf(" %d. Disconnect %s\n", i+1, server)
 	}
 	fmt.Printf(" %d. Connect another server\n", len(w.conf.Servers)+1)
@@ -40,14 +42,14 @@ func (w *wizard) manageServers() {
 	}
 	// If the user selected an existing server, drop it
 	if choice <= len(w.conf.Servers) {
-		server := w.conf.Servers[choice-1]
+		server := servers[choice-1]
 		client := w.servers[server]
 
 		delete(w.servers, server)
 		if client != nil {
 			client.Close()
 		}
-		w.conf.Servers = append(w.conf.Servers[:choice-1], w.conf.Servers[choice:]...)
+		delete(w.conf.Servers, server)
 		w.conf.flush()
 
 		log.Info("Disconnected existing server", "server", server)
@@ -73,14 +75,14 @@ func (w *wizard) makeServer() string {
 		// Read and fial the server to ensure docker is present
 		input := w.readString()
 
-		client, err := dial(input)
+		client, err := dial(input, nil)
 		if err != nil {
 			log.Error("Server not ready for puppeth", "err", err)
 			return ""
 		}
 		// All checks passed, start tracking the server
 		w.servers[input] = client
-		w.conf.Servers = append(w.conf.Servers, input)
+		w.conf.Servers[input] = client.pubkey
 		w.conf.flush()
 
 		return input
@@ -93,7 +95,9 @@ func (w *wizard) selectServer() string {
 	// List the available server to the user and wait for a choice
 	fmt.Println()
 	fmt.Println("Which server do you want to interact with?")
-	for i, server := range w.conf.Servers {
+
+	servers := w.conf.servers()
+	for i, server := range servers {
 		fmt.Printf(" %d. %s\n", i+1, server)
 	}
 	fmt.Printf(" %d. Connect another server\n", len(w.conf.Servers)+1)
@@ -105,7 +109,7 @@ func (w *wizard) selectServer() string {
 	}
 	// If the user requested connecting to a new server, go for it
 	if choice <= len(w.conf.Servers) {
-		return w.conf.Servers[choice-1]
+		return servers[choice-1]
 	}
 	return w.makeServer()
 }