Load user profile when SSH (#380)

This PR fixes issues with the terminal when
running netbird ssh to a remote agent.
Every session looks up a user and loads its
profile. If no user is found, the connection is rejected.
The default user is root.

client/cmd/ssh.go

@@ -17,7 +17,7 @@ import (
 
 var (
 	port int
-	user = "netbird"
+	user = "root"
 	host string
 )
 
@@ -90,7 +90,8 @@ func runSSH(ctx context.Context, addr string, pemKey []byte, cmd *cobra.Command)
 		cmd.Printf("Couldn't connect. " +
 			"You might be disconnected from the NetBird network, or the NetBird agent isn't running.\n" +
 			"Run the status command: \n\n" +
-			" netbird status\n\n")
+			" netbird status\n\n" +
+			"It might also be that the SSH server is disabled on the agent you are trying to connect to.\n")
 		return nil
 	}
 	go func() {

client/internal/engine.go

@@ -7,6 +7,7 @@ import (
 	nbstatus "github.com/netbirdio/netbird/client/status"
 	"math/rand"
 	"net"
+	"reflect"
 	"runtime"
 	"strings"
 	"sync"
@@ -174,6 +175,13 @@ func (e *Engine) Stop() error {
 		}
 	}
 
+	if !isNil(e.sshServer) {
+		err := e.sshServer.Stop()
+		if err != nil {
+			log.Warnf("failed stopping the SSH server: %v", err)
+		}
+	}
+
 	log.Infof("stopped Netbird Engine")
 
 	return nil
@@ -301,7 +309,7 @@ func (e *Engine) removeAllPeers() error {
 func (e *Engine) removePeer(peerKey string) error {
 	log.Debugf("removing peer from engine %s", peerKey)
 
-	if e.sshServer != nil {
+	if !isNil(e.sshServer) {
 		e.sshServer.RemoveAuthorizedKey(peerKey)
 	}
 
@@ -434,14 +442,18 @@ func (e *Engine) handleSync(update *mgmProto.SyncResponse) error {
 	return nil
 }
 
+func isNil(server nbssh.Server) bool {
+	return server == nil || reflect.ValueOf(server).IsNil()
+}
+
 func (e *Engine) updateSSH(sshConf *mgmProto.SSHConfig) error {
 	if sshConf.GetSshEnabled() {
 		if runtime.GOOS == "windows" {
 			log.Warnf("running SSH server on Windows is not supported")
 			return nil
 		}
 		// start SSH server if it wasn't running
-		if e.sshServer == nil {
+		if isNil(e.sshServer) {
 			//nil sshServer means it has not yet been started
 			var err error
 			e.sshServer, err = e.sshServerFunc(e.config.SSHKey,
@@ -466,7 +478,7 @@ func (e *Engine) updateSSH(sshConf *mgmProto.SSHConfig) error {
 		}
 	} else {
 		// Disable SSH server request, so stop it if it was running
-		if e.sshServer != nil {
+		if !isNil(e.sshServer) {
 			err := e.sshServer.Stop()
 			if err != nil {
 				log.Warnf("failed to stop SSH server %v", err)
@@ -597,7 +609,7 @@ func (e *Engine) updateNetworkMap(networkMap *mgmProto.NetworkMap) error {
 		}
 
 		// update SSHServer by adding remote peer SSH keys
-		if e.sshServer != nil {
+		if !isNil(e.sshServer) {
 			for _, config := range networkMap.GetRemotePeers() {
 				if config.GetSshConfig() != nil && config.GetSshConfig().GetSshPubKey() != nil {
 					err := e.sshServer.AddAuthorizedKey(config.WgPubKey, string(config.GetSshConfig().GetSshPubKey()))

client/ssh/login.go

@@ -0,0 +1,36 @@
+package ssh
+
+import (
+	"fmt"
+	"github.com/netbirdio/netbird/util"
+	"net"
+	"net/netip"
+	"os/exec"
+	"runtime"
+)
+
+func getLoginCmd(user string, remoteAddr net.Addr) (loginPath string, args []string, err error) {
+	loginPath, err = exec.LookPath("login")
+	if err != nil {
+		return "", nil, err
+	}
+
+	addrPort, err := netip.ParseAddrPort(remoteAddr.String())
+	if err != nil {
+		return "", nil, err
+	}
+
+	if runtime.GOOS == "linux" {
+
+		if util.FileExists("/etc/arch-release") && !util.FileExists("/etc/pam.d/remote") {
+			// detect if Arch Linux
+			return loginPath, []string{"-f", user, "-p"}, nil
+		}
+
+		return loginPath, []string{"-f", user, "-h", addrPort.Addr().String(), "-p"}, nil
+	} else if runtime.GOOS == "darwin" {
+		return loginPath, []string{"-fp", "-h", addrPort.Addr().String(), user}, nil
+	}
+
+	return "", nil, fmt.Errorf("unsupported platform")
+}

client/ssh/server.go

@@ -9,6 +9,9 @@ import (
 	"net"
 	"os"
 	"os/exec"
+	"os/user"
+	"runtime"
+	"strings"
 	"sync"
 )
 
@@ -105,27 +108,75 @@ func (srv *DefaultServer) publicKeyHandler(ctx ssh.Context, key ssh.PublicKey) b
 	return false
 }
 
-func getShellType() string {
-	shell := os.Getenv("SHELL")
-	if shell == "" {
-		shell = "sh"
+func prepareUserEnv(user *user.User, shell string) []string {
+	return []string{
+		fmt.Sprintf("SHELL=" + shell),
+		fmt.Sprintf("USER=" + user.Username),
+		fmt.Sprintf("HOME=" + user.HomeDir),
 	}
-	return shell
+}
+
+func acceptEnv(s string) bool {
+	split := strings.Split(s, "=")
+	if len(split) != 2 {
+		return false
+	}
+	return split[0] == "TERM" || split[0] == "LANG" || strings.HasPrefix(split[0], "LC_")
 }
 
 // sessionHandler handles SSH session post auth
 func (srv *DefaultServer) sessionHandler(session ssh.Session) {
 	srv.mu.Lock()
 	srv.sessions = append(srv.sessions, session)
 	srv.mu.Unlock()
+
+	defer func() {
+		err := session.Close()
+		if err != nil {
+			return
+		}
+	}()
+
+	localUser, err := user.Lookup(session.User())
+	if err != nil {
+		_, err = fmt.Fprintf(session, "remote SSH server couldn't find local user %s\n", session.User()) //nolint
+		err = session.Exit(1)
+		if err != nil {
+			return
+		}
+		log.Warnf("failed SSH session from %v, user %s", session.RemoteAddr(), session.User())
+		return
+	}
+
 	ptyReq, winCh, isPty := session.Pty()
 	if isPty {
-		cmd := exec.Command(getShellType())
-		cmd.Env = append(cmd.Env, fmt.Sprintf("TERM=%session", ptyReq.Term))
+		loginCmd, loginArgs, err := getLoginCmd(localUser.Username, session.RemoteAddr())
+		if err != nil {
+			log.Warnf("failed logging-in user %s from remote IP %s", localUser.Username, session.RemoteAddr().String())
+			return
+		}
+		cmd := exec.Command(loginCmd, loginArgs...)
+		go func() {
+			<-session.Context().Done()
+			err := cmd.Process.Kill()
+			if err != nil {
+				return
+			}
+		}()
+		cmd.Dir = localUser.HomeDir
+		cmd.Env = append(cmd.Env, fmt.Sprintf("TERM=%s", ptyReq.Term))
+		cmd.Env = append(cmd.Env, prepareUserEnv(localUser, getUserShell(localUser.Uid))...)
+		for _, v := range session.Environ() {
+			if acceptEnv(v) {
+				cmd.Env = append(cmd.Env, v)
+			}
+		}
+
 		file, err := pty.Start(cmd)
 		if err != nil {
 			log.Errorf("failed starting SSH server %v", err)
 		}
+
 		go func() {
 			for win := range winCh {
 				setWinSize(file, win.Width, win.Height)
@@ -181,3 +232,19 @@ func (srv *DefaultServer) Start() error {
 
 	return nil
 }
+
+func getUserShell(userID string) string {
+	if runtime.GOOS == "linux" {
+		output, _ := exec.Command("getent", "passwd", userID).Output()
+		line := strings.SplitN(string(output), ":", 10)
+		if len(line) > 6 {
+			return strings.TrimSpace(line[6])
+		}
+	}
+
+	shell := os.Getenv("SHELL")
+	if shell == "" {
+		shell = "/bin/sh"
+	}
+	return shell
+}

util/common.go

@@ -1,5 +1,7 @@
 package util
 
+import "os"
+
 // SliceDiff returns the elements in slice `x` that are not in slice `y`
 func SliceDiff(x, y []string) []string {
 	mapY := make(map[string]struct{}, len(y))
@@ -14,3 +16,9 @@ func SliceDiff(x, y []string) []string {
 	}
 	return diff
 }
+
+// FileExists returns true if specified file exists
+func FileExists(path string) bool {
+	_, err := os.Stat(path)
+	return err == nil
+}