[client, android] Expose ssh functionality for Android (#7156)

Adds an SSHClient gomobile binding so the Android app can run an SSH session over the tunnel with a PTY, exposed through a listener interface for the in-app terminal.

Server type is auto-detected from the SSH banner, which selects the auth path: JWT device-code flow, NetBird key, or a regular server (NetBird key first, then password). Host keys are verified against the peer registry for NetBird servers and trust-on-first-use for regular ones.

client/ssh/client/client.go

@@ -313,21 +313,23 @@ func Dial(ctx context.Context, addr, user string, opts DialOptions) (*Client, er
 
 // dialSSH establishes an SSH connection without JWT authentication
 func dialSSH(ctx context.Context, network, addr string, config *ssh.ClientConfig) (*Client, error) {
+	if config.Timeout > 0 {
+		var cancel context.CancelFunc
+		ctx, cancel = context.WithTimeout(ctx, config.Timeout)
+		defer cancel()
+	}
+
 	dialer := &net.Dialer{}
 	conn, err := dialer.DialContext(ctx, network, addr)
 	if err != nil {
 		return nil, fmt.Errorf("dial %s: %w", addr, err)
 	}
 
-	clientConn, chans, reqs, err := ssh.NewClientConn(conn, addr, config)
+	client, err := nbssh.Handshake(ctx, conn, addr, config)
 	if err != nil {
-		if closeErr := conn.Close(); closeErr != nil {
-			log.Debugf("connection close after handshake failure: %v", closeErr)
-		}
-		return nil, fmt.Errorf("ssh handshake: %w", err)
+		return nil, err
 	}
 
-	client := ssh.NewClient(clientConn, chans, reqs)
 	return &Client{
 		client: client,
 	}, nil

client/ssh/client/terminal_unix.go

@@ -12,6 +12,8 @@ import (
 	log "github.com/sirupsen/logrus"
 	"golang.org/x/crypto/ssh"
 	"golang.org/x/term"
+
+	nbssh "github.com/netbirdio/netbird/client/ssh"
 )
 
 func (c *Client) setupTerminalMode(ctx context.Context, session *ssh.Session) error {
@@ -82,37 +84,7 @@ func (c *Client) setupTerminal(session *ssh.Session, fd int) error {
 		return fmt.Errorf("get terminal size: %w", err)
 	}
 
-	modes := ssh.TerminalModes{
-		ssh.ECHO:          1,
-		ssh.TTY_OP_ISPEED: 14400,
-		ssh.TTY_OP_OSPEED: 14400,
-		// Ctrl+C
-		ssh.VINTR: 3,
-		// Ctrl+\
-		ssh.VQUIT: 28,
-		// Backspace
-		ssh.VERASE: 127,
-		// Ctrl+U
-		ssh.VKILL: 21,
-		// Ctrl+D
-		ssh.VEOF:  4,
-		ssh.VEOL:  0,
-		ssh.VEOL2: 0,
-		// Ctrl+Q
-		ssh.VSTART: 17,
-		// Ctrl+S
-		ssh.VSTOP: 19,
-		// Ctrl+Z
-		ssh.VSUSP: 26,
-		// Ctrl+O
-		ssh.VDISCARD: 15,
-		// Ctrl+R
-		ssh.VREPRINT: 18,
-		// Ctrl+W
-		ssh.VWERASE: 23,
-		// Ctrl+V
-		ssh.VLNEXT: 22,
-	}
+	modes := nbssh.DefaultTerminalModes
 
 	terminal := os.Getenv("TERM")
 	if terminal == "" {

client/ssh/client/terminal_windows.go

@@ -10,6 +10,8 @@ import (
 
 	log "github.com/sirupsen/logrus"
 	"golang.org/x/crypto/ssh"
+
+	nbssh "github.com/netbirdio/netbird/client/ssh"
 )
 
 const (
@@ -80,28 +82,14 @@ func (c *Client) setupTerminalMode(_ context.Context, session *ssh.Session) erro
 	w, h := c.getWindowsConsoleSize()
 
 	modes := ssh.TerminalModes{
-		ssh.ECHO:          1,
-		ssh.TTY_OP_ISPEED: 14400,
-		ssh.TTY_OP_OSPEED: 14400,
-		ssh.ICRNL:         1,
-		ssh.OPOST:         1,
-		ssh.ONLCR:         1,
-		ssh.ISIG:          1,
-		ssh.ICANON:        1,
-		ssh.VINTR:         3,   // Ctrl+C
-		ssh.VQUIT:         28,  // Ctrl+\
-		ssh.VERASE:        127, // Backspace
-		ssh.VKILL:         21,  // Ctrl+U
-		ssh.VEOF:          4,   // Ctrl+D
-		ssh.VEOL:          0,
-		ssh.VEOL2:         0,
-		ssh.VSTART:        17, // Ctrl+Q
-		ssh.VSTOP:         19, // Ctrl+S
-		ssh.VSUSP:         26, // Ctrl+Z
-		ssh.VDISCARD:      15, // Ctrl+O
-		ssh.VWERASE:       23, // Ctrl+W
-		ssh.VLNEXT:        22, // Ctrl+V
-		ssh.VREPRINT:      18, // Ctrl+R
+		ssh.ICRNL:  1,
+		ssh.OPOST:  1,
+		ssh.ONLCR:  1,
+		ssh.ISIG:   1,
+		ssh.ICANON: 1,
+	}
+	for mode, value := range nbssh.DefaultTerminalModes {
+		modes[mode] = value
 	}
 
 	if err := session.RequestPty("xterm-256color", h, w, modes); err != nil {

client/ssh/common.go

@@ -35,6 +35,19 @@ type HostKeyVerifier interface {
 	VerifySSHHostKey(peerAddress string, key []byte) error
 }
 
+// PeerKeyLookup returns the stored SSH host key for a peer address.
+type PeerKeyLookup func(peerAddress string) ([]byte, bool)
+
+// VerifySSHHostKey implements HostKeyVerifier by looking up the stored key
+// and comparing it against the presented key.
+func (l PeerKeyLookup) VerifySSHHostKey(peerAddress string, presentedKey []byte) error {
+	storedKey, found := l(peerAddress)
+	if !found {
+		return ErrPeerNotFound
+	}
+	return VerifyHostKey(storedKey, presentedKey, peerAddress)
+}
+
 // DaemonHostKeyVerifier implements HostKeyVerifier using the NetBird daemon
 type DaemonHostKeyVerifier struct {
 	client proto.DaemonServiceClient

client/ssh/handshake.go

@@ -0,0 +1,45 @@
+package ssh
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"net"
+	"time"
+
+	log "github.com/sirupsen/logrus"
+	"golang.org/x/crypto/ssh"
+)
+
+// Handshake runs the SSH client handshake on an already dialed conn and
+// returns the resulting client. Dialing bounds only the TCP establishment;
+// without a deadline on the socket a peer that accepts and then goes silent
+// blocks the handshake forever, so the context deadline is applied to conn
+// for the duration of the handshake. conn is closed on any error.
+func Handshake(ctx context.Context, conn net.Conn, addr string, config *ssh.ClientConfig) (*ssh.Client, error) {
+	if deadline, ok := ctx.Deadline(); ok {
+		if err := conn.SetDeadline(deadline); err != nil {
+			closeHandshake(conn, "conn after deadline error")
+			return nil, fmt.Errorf("set handshake deadline: %w", err)
+		}
+	}
+
+	sshConn, chans, reqs, err := ssh.NewClientConn(conn, addr, config)
+	if err != nil {
+		closeHandshake(conn, "conn after handshake error")
+		return nil, fmt.Errorf("ssh handshake: %w", err)
+	}
+
+	if err := conn.SetDeadline(time.Time{}); err != nil {
+		closeHandshake(sshConn, "ssh conn after deadline clear error")
+		return nil, fmt.Errorf("clear handshake deadline: %w", err)
+	}
+
+	return ssh.NewClient(sshConn, chans, reqs), nil
+}
+
+func closeHandshake(c io.Closer, label string) {
+	if err := c.Close(); err != nil {
+		log.Debugf("ssh: close %s: %v", label, err)
+	}
+}

client/ssh/proxy/proxy.go

@@ -610,13 +610,10 @@ func (p *SSHProxy) dialBackend(ctx context.Context, addr, user, jwtToken string)
 		return nil, fmt.Errorf("connect to server: %w", err)
 	}
 
-	clientConn, chans, reqs, err := cryptossh.NewClientConn(conn, addr, config)
-	if err != nil {
-		_ = conn.Close()
-		return nil, fmt.Errorf("SSH handshake: %w", err)
-	}
+	handshakeCtx, cancel := context.WithTimeout(ctx, sshHandshakeTimeout)
+	defer cancel()
 
-	return cryptossh.NewClient(clientConn, chans, reqs), nil
+	return nbssh.Handshake(handshakeCtx, conn, addr, config)
 }
 
 func (p *SSHProxy) verifyHostKey(hostname string, remote net.Addr, key cryptossh.PublicKey) error {

client/ssh/session.go

@@ -0,0 +1,84 @@
+package ssh
+
+import (
+	"fmt"
+	"io"
+
+	log "github.com/sirupsen/logrus"
+	"golang.org/x/crypto/ssh"
+)
+
+// DefaultTerminalModes are the PTY modes used by the interactive terminal clients.
+var DefaultTerminalModes = ssh.TerminalModes{
+	ssh.ECHO:          1,
+	ssh.TTY_OP_ISPEED: 14400,
+	ssh.TTY_OP_OSPEED: 14400,
+	ssh.VINTR:         3,   // Ctrl+C
+	ssh.VQUIT:         28,  // Ctrl+\
+	ssh.VERASE:        127, // Backspace
+	ssh.VKILL:         21,  // Ctrl+U
+	ssh.VEOF:          4,   // Ctrl+D
+	ssh.VEOL:          0,
+	ssh.VEOL2:         0,
+	ssh.VSTART:        17, // Ctrl+Q
+	ssh.VSTOP:         19, // Ctrl+S
+	ssh.VSUSP:         26, // Ctrl+Z
+	ssh.VDISCARD:      15, // Ctrl+O
+	ssh.VREPRINT:      18, // Ctrl+R
+	ssh.VWERASE:       23, // Ctrl+W
+	ssh.VLNEXT:        22, // Ctrl+V
+}
+
+// PTYSession is an interactive shell session with a PTY and its I/O pipes.
+type PTYSession struct {
+	Session *ssh.Session
+	Stdin   io.WriteCloser
+	Stdout  io.Reader
+	Stderr  io.Reader
+}
+
+// StartPTYSession opens a session on the client, requests an xterm-256color PTY
+// with the default terminal modes, wires up the I/O pipes and starts a shell.
+// The session is closed on any error.
+func StartPTYSession(client *ssh.Client, cols, rows int) (*PTYSession, error) {
+	session, err := client.NewSession()
+	if err != nil {
+		return nil, fmt.Errorf("new session: %w", err)
+	}
+
+	pty, err := setupPTYSession(session, cols, rows)
+	if err != nil {
+		if closeErr := session.Close(); closeErr != nil {
+			log.Debugf("ssh: session close after setup error: %v", closeErr)
+		}
+		return nil, err
+	}
+	return pty, nil
+}
+
+// setupPTYSession requests the PTY, opens the pipes and starts the shell on an
+// already created session.
+func setupPTYSession(session *ssh.Session, cols, rows int) (*PTYSession, error) {
+	if err := session.RequestPty("xterm-256color", rows, cols, DefaultTerminalModes); err != nil {
+		return nil, fmt.Errorf("request pty: %w", err)
+	}
+
+	stdin, err := session.StdinPipe()
+	if err != nil {
+		return nil, fmt.Errorf("stdin pipe: %w", err)
+	}
+	stdout, err := session.StdoutPipe()
+	if err != nil {
+		return nil, fmt.Errorf("stdout pipe: %w", err)
+	}
+	stderr, err := session.StderrPipe()
+	if err != nil {
+		return nil, fmt.Errorf("stderr pipe: %w", err)
+	}
+
+	if err := session.Shell(); err != nil {
+		return nil, fmt.Errorf("start shell: %w", err)
+	}
+
+	return &PTYSession{Session: session, Stdin: stdin, Stdout: stdout, Stderr: stderr}, nil
+}