[client] Allow ssh server on freebsd (#3170)

* Enable ssh server on freebsd

* Fix listening in netstack mode

* Fix panic if login cmd fails

* Tidy up go mod

client/ssh/login.go

@@ -2,14 +2,29 @@ package ssh
 
 import (
 	"fmt"
-	"github.com/netbirdio/netbird/util"
 	"net"
 	"net/netip"
+	"os"
 	"os/exec"
 	"runtime"
+
+	"github.com/netbirdio/netbird/util"
 )
 
+func isRoot() bool {
+	return os.Geteuid() == 0
+}
+
 func getLoginCmd(user string, remoteAddr net.Addr) (loginPath string, args []string, err error) {
+	if !isRoot() {
+		shell := getUserShell(user)
+		if shell == "" {
+			shell = "/bin/sh"
+		}
+
+		return shell, []string{"-l"}, nil
+	}
+
 	loginPath, err = exec.LookPath("login")
 	if err != nil {
 		return "", nil, err
@@ -20,17 +35,17 @@ func getLoginCmd(user string, remoteAddr net.Addr) (loginPath string, args []str
 		return "", nil, err
 	}
 
-	if runtime.GOOS == "linux" {
-
+	switch runtime.GOOS {
+	case "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" {
+	case "darwin":
 		return loginPath, []string{"-fp", "-h", addrPort.Addr().String(), user}, nil
+	case "freebsd":
+		return loginPath, []string{"-f", user, "-h", addrPort.Addr().String(), "-p"}, nil
+	default:
+		return "", nil, fmt.Errorf("unsupported platform: %s", runtime.GOOS)
 	}
-
-	return "", nil, fmt.Errorf("unsupported platform")
 }

client/ssh/lookup.go

@@ -6,5 +6,9 @@ package ssh
 import "os/user"
 
 func userNameLookup(username string) (*user.User, error) {
+	if username == "" || (username == "root" && !isRoot()) {
+		return user.Current()
+	}
+
 	return user.Lookup(username)
 }

client/ssh/lookup_darwin.go

@@ -12,6 +12,10 @@ import (
 )
 
 func userNameLookup(username string) (*user.User, error) {
+	if username == "" || (username == "root" && !isRoot()) {
+		return user.Current()
+	}
+
 	var userObject *user.User
 	userObject, err := user.Lookup(username)
 	if err != nil && err.Error() == user.UnknownUserError(username).Error() {

client/ssh/server.go

@@ -168,8 +168,12 @@ func (srv *DefaultServer) sessionHandler(session ssh.Session) {
 		cmd := exec.Command(loginCmd, loginArgs...)
 		go func() {
 			<-session.Context().Done()
+			if cmd.Process == nil {
+				return
+			}
 			err := cmd.Process.Kill()
 			if err != nil {
+				log.Debugf("failed killing SSH process %v", err)
 				return
 			}
 		}()
@@ -185,7 +189,7 @@ func (srv *DefaultServer) sessionHandler(session ssh.Session) {
 		log.Debugf("Login command: %s", cmd.String())
 		file, err := pty.Start(cmd)
 		if err != nil {
-			log.Errorf("failed starting SSH server %v", err)
+			log.Errorf("failed starting SSH server: %v", err)
 		}
 
 		go func() {