[client, management] Add embedded VNC server

client/cmd/up.go

@@ -426,6 +426,16 @@ func setSSHSetConfigFields(req *proto.SetConfigRequest, cmd *cobra.Command) {
 	}
 }
 
+// setVNCSetConfigFields is setSSHSetConfigFields for the VNC server flags.
+func setVNCSetConfigFields(req *proto.SetConfigRequest, cmd *cobra.Command) {
+	if cmd.Flag(serverVNCAllowedFlag).Changed {
+		req.ServerVNCAllowed = &serverVNCAllowed
+	}
+	if cmd.Flag(disableVNCApprovalFlag).Changed {
+		req.DisableVNCApproval = &disableVNCApproval
+	}
+}
+
 func setupSetConfigReq(customDNSAddressConverted []byte, cmd *cobra.Command, profileName, username string) *proto.SetConfigRequest {
 	var req proto.SetConfigRequest
 	req.ProfileName = profileName
@@ -447,6 +457,7 @@ func setupSetConfigReq(customDNSAddressConverted []byte, cmd *cobra.Command, pro
 		req.RosenpassPermissive = &rosenpassPermissive
 	}
 	setSSHSetConfigFields(&req, cmd)
+	setVNCSetConfigFields(&req, cmd)
 
 	if cmd.Flag(interfaceNameFlag).Changed {
 		if err := parseInterfaceName(interfaceName); err != nil {
@@ -475,46 +486,50 @@ func setupSetConfigReq(customDNSAddressConverted []byte, cmd *cobra.Command, pro
 		req.DisableAutoConnect = &autoConnectDisabled
 	}
 
+	setNetworkSetConfigFields(&req, cmd)
+	setLocalMetricsSetConfigFields(&req, cmd)
+
+	return &req
+}
+
+// setNetworkSetConfigFields copies the routing, DNS and firewall toggles the
+// user actually passed into req.
+func setNetworkSetConfigFields(req *proto.SetConfigRequest, cmd *cobra.Command) {
 	if cmd.Flag(dnsRouteIntervalFlag).Changed {
 		req.DnsRouteInterval = durationpb.New(dnsRouteInterval)
 	}
-
 	if cmd.Flag(disableClientRoutesFlag).Changed {
 		req.DisableClientRoutes = &disableClientRoutes
 	}
-
 	if cmd.Flag(disableServerRoutesFlag).Changed {
 		req.DisableServerRoutes = &disableServerRoutes
 	}
-
 	if cmd.Flag(disableDNSFlag).Changed {
 		req.DisableDns = &disableDNS
 	}
-
 	if cmd.Flag(disableFirewallFlag).Changed {
 		req.DisableFirewall = &disableFirewall
 	}
-
 	if cmd.Flag(blockLANAccessFlag).Changed {
 		req.BlockLanAccess = &blockLANAccess
 	}
-
 	if cmd.Flag(blockInboundFlag).Changed {
 		req.BlockInbound = &blockInbound
 	}
-
 	if cmd.Flag(disableIPv6Flag).Changed {
 		req.DisableIpv6 = &disableIPv6
 	}
+}
 
+// setLocalMetricsSetConfigFields copies the local metrics endpoint flags the
+// user actually passed into req.
+func setLocalMetricsSetConfigFields(req *proto.SetConfigRequest, cmd *cobra.Command) {
 	if cmd.Flag(enableLocalMetricsFlag).Changed {
 		req.EnableLocalMetrics = &localMetricsEnabled
 	}
 	if cmd.Flag(localMetricsAddressFlag).Changed {
 		req.LocalMetricsAddress = &localMetricsAddr
 	}
-
-	return &req
 }
 
 func setupConfig(customDNSAddressConverted []byte, cmd *cobra.Command, configFilePath string) (*profilemanager.ConfigInput, error) {
@@ -538,30 +553,14 @@ func setupConfig(customDNSAddressConverted []byte, cmd *cobra.Command, configFil
 	if cmd.Flag(serverSSHAllowedFlag).Changed {
 		ic.ServerSSHAllowed = &serverSSHAllowed
 	}
-
-	if cmd.Flag(enableSSHRootFlag).Changed {
-		ic.EnableSSHRoot = &enableSSHRoot
-	}
-
-	if cmd.Flag(enableSSHSFTPFlag).Changed {
-		ic.EnableSSHSFTP = &enableSSHSFTP
+	if cmd.Flag(serverVNCAllowedFlag).Changed {
+		ic.ServerVNCAllowed = &serverVNCAllowed
 	}
-
-	if cmd.Flag(enableSSHLocalPortForwardFlag).Changed {
-		ic.EnableSSHLocalPortForwarding = &enableSSHLocalPortForward
+	if cmd.Flag(disableVNCApprovalFlag).Changed {
+		ic.DisableVNCApproval = &disableVNCApproval
 	}
 
-	if cmd.Flag(enableSSHRemotePortForwardFlag).Changed {
-		ic.EnableSSHRemotePortForwarding = &enableSSHRemotePortForward
-	}
-
-	if cmd.Flag(disableSSHAuthFlag).Changed {
-		ic.DisableSSHAuth = &disableSSHAuth
-	}
-
-	if cmd.Flag(sshJWTCacheTTLFlag).Changed {
-		ic.SSHJWTCacheTTL = &sshJWTCacheTTL
-	}
+	applySSHFlagsToConfig(cmd, &ic)
 
 	if cmd.Flag(interfaceNameFlag).Changed {
 		if err := parseInterfaceName(interfaceName); err != nil {
@@ -642,6 +641,27 @@ func setupConfig(customDNSAddressConverted []byte, cmd *cobra.Command, configFil
 	return &ic, nil
 }
 
+func applySSHFlagsToConfig(cmd *cobra.Command, ic *profilemanager.ConfigInput) {
+	if cmd.Flag(enableSSHRootFlag).Changed {
+		ic.EnableSSHRoot = &enableSSHRoot
+	}
+	if cmd.Flag(enableSSHSFTPFlag).Changed {
+		ic.EnableSSHSFTP = &enableSSHSFTP
+	}
+	if cmd.Flag(enableSSHLocalPortForwardFlag).Changed {
+		ic.EnableSSHLocalPortForwarding = &enableSSHLocalPortForward
+	}
+	if cmd.Flag(enableSSHRemotePortForwardFlag).Changed {
+		ic.EnableSSHRemotePortForwarding = &enableSSHRemotePortForward
+	}
+	if cmd.Flag(disableSSHAuthFlag).Changed {
+		ic.DisableSSHAuth = &disableSSHAuth
+	}
+	if cmd.Flag(sshJWTCacheTTLFlag).Changed {
+		ic.SSHJWTCacheTTL = &sshJWTCacheTTL
+	}
+}
+
 // setSSHLoginFields copies the SSH server flags the user actually passed
 // into req, leaving the rest unset so the daemon keeps the persisted
 // values.
@@ -670,6 +690,16 @@ func setSSHLoginFields(req *proto.LoginRequest, cmd *cobra.Command) {
 	}
 }
 
+// setVNCLoginFields is setSSHLoginFields for the VNC server flags.
+func setVNCLoginFields(req *proto.LoginRequest, cmd *cobra.Command) {
+	if cmd.Flag(serverVNCAllowedFlag).Changed {
+		req.ServerVNCAllowed = &serverVNCAllowed
+	}
+	if cmd.Flag(disableVNCApprovalFlag).Changed {
+		req.DisableVNCApproval = &disableVNCApproval
+	}
+}
+
 func setupLoginRequest(providedSetupKey string, customDNSAddressConverted []byte, cmd *cobra.Command) (*proto.LoginRequest, error) {
 	loginRequest := proto.LoginRequest{
 		SetupKey:            providedSetupKey,
@@ -697,6 +727,7 @@ func setupLoginRequest(providedSetupKey string, customDNSAddressConverted []byte
 	}
 
 	setSSHLoginFields(&loginRequest, cmd)
+	setVNCLoginFields(&loginRequest, cmd)
 
 	if cmd.Flag(disableAutoConnectFlag).Changed {
 		loginRequest.DisableAutoConnect = &autoConnectDisabled

client/cmd/vnc_agent.go

@@ -0,0 +1,104 @@
+//go:build windows || (darwin && !ios)
+
+package cmd
+
+import (
+	"fmt"
+	"net"
+	"net/netip"
+	"os"
+
+	log "github.com/sirupsen/logrus"
+	"github.com/spf13/cobra"
+
+	vncserver "github.com/netbirdio/netbird/client/vnc/server"
+)
+
+var (
+	vncAgentSocket    string
+	vncAgentTargetUID uint32
+)
+
+func init() {
+	vncAgentCmd.Flags().StringVar(&vncAgentSocket, "socket", "", "Unix-domain socket path the agent listens on (required)")
+	vncAgentCmd.Flags().Uint32Var(&vncAgentTargetUID, "target-uid", 0, "uid the agent drops privileges to before listening (darwin only; required there, and must not be 0)")
+	rootCmd.AddCommand(vncAgentCmd)
+}
+
+// vncAgentCmd runs a VNC server inside the user's interactive session,
+// listening on a Unix-domain socket. The NetBird service spawns it: on
+// Windows via CreateProcessAsUser into the console session, on macOS via
+// launchctl asuser into the Aqua session.
+var vncAgentCmd = &cobra.Command{
+	Use:    "vnc-agent",
+	Short:  "Run VNC capture agent (internal, spawned by service)",
+	Hidden: true,
+	RunE: func(cmd *cobra.Command, args []string) error {
+		log.SetReportCaller(true)
+		log.SetFormatter(&log.JSONFormatter{})
+		log.SetOutput(os.Stderr)
+
+		if vncAgentSocket == "" {
+			return fmt.Errorf("--socket is required")
+		}
+
+		token := os.Getenv("NB_VNC_AGENT_TOKEN")
+		if token == "" {
+			return fmt.Errorf("NB_VNC_AGENT_TOKEN not set; agent requires a token from the service")
+		}
+		// Purge the token from env so it doesn't leak via /proc/<pid>/environ.
+		if err := os.Unsetenv("NB_VNC_AGENT_TOKEN"); err != nil {
+			log.Debugf("unset NB_VNC_AGENT_TOKEN: %v", err)
+		}
+
+		// Drop root privileges to the target console user BEFORE creating
+		// the listening socket: keeps a post-auth bug in the encoder /
+		// input / capture paths confined to the user's own privileges
+		// rather than escalating to host root, and makes the daemon's
+		// LOCAL_PEERCRED check see the right uid. No-op on Windows, where
+		// both processes run as SYSTEM.
+		//
+		// Called unconditionally: a missing or zero --target-uid is exactly
+		// the case the Darwin implementation refuses, and skipping the call
+		// for it would leave the agent running as root instead.
+		if err := dropAgentPrivileges(vncAgentTargetUID); err != nil {
+			return fmt.Errorf("drop privileges to uid %d: %w", vncAgentTargetUID, err)
+		}
+
+		if err := os.Remove(vncAgentSocket); err != nil && !os.IsNotExist(err) {
+			log.Debugf("remove stale socket %s: %v", vncAgentSocket, err)
+		}
+		ln, err := net.Listen("unix", vncAgentSocket)
+		if err != nil {
+			return fmt.Errorf("listen on %s: %w", vncAgentSocket, err)
+		}
+		if err := os.Chmod(vncAgentSocket, 0o600); err != nil {
+			log.Debugf("chmod %s: %v", vncAgentSocket, err)
+		}
+
+		ctx := cmd.Context()
+
+		capturer, injector, err := newAgentResources()
+		if err != nil {
+			_ = ln.Close()
+			return err
+		}
+		srv := vncserver.New(vncserver.Config{
+			Capturer:      capturer,
+			Injector:      injector,
+			DisableAuth:   true,
+			AgentTokenHex: token,
+			Listener:      ln,
+		})
+
+		if err := srv.Start(ctx, netip.AddrPort{}, netip.Prefix{}); err != nil {
+			return fmt.Errorf("start vnc server: %w", err)
+		}
+		log.Infof("vnc-agent listening on %s, ready", vncAgentSocket)
+
+		<-ctx.Done()
+		log.Info("vnc-agent context cancelled, shutting down")
+		return srv.Stop()
+	},
+	SilenceUsage: true,
+}

client/cmd/vnc_agent_darwin.go

@@ -0,0 +1,25 @@
+//go:build darwin && !ios
+
+package cmd
+
+import (
+	"fmt"
+
+	vncserver "github.com/netbirdio/netbird/client/vnc/server"
+)
+
+func newAgentResources() (vncserver.ScreenCapturer, vncserver.InputInjector, error) {
+	// Ask for Screen Recording here and nowhere else. This process runs as the
+	// console user, which TCC requires for a user-scope service, and it is fresh
+	// per connection, which is what makes the dialog appear at all: TCC shows it
+	// once per process. The request blocks until the user answers, so it also
+	// keeps the Accessibility ask that follows the first input out of its way.
+	vncserver.RequestScreenRecording()
+
+	capturer := vncserver.NewMacPoller()
+	injector, err := vncserver.NewMacInputInjector()
+	if err != nil {
+		return nil, nil, fmt.Errorf("macOS input injector: %w", err)
+	}
+	return capturer, injector, nil
+}

client/cmd/vnc_agent_dropprivs_darwin.go

@@ -0,0 +1,77 @@
+//go:build darwin && !ios
+
+package cmd
+
+import (
+	"fmt"
+	"os"
+	"os/user"
+	"strconv"
+	"syscall"
+)
+
+// dropAgentPrivileges drops the vnc-agent process from root (its
+// launchctl-asuser-inherited starting uid) to the target console user
+// before any other initialisation runs. Without this the agent runs as
+// root for the lifetime of the session; any post-auth memory-safety
+// issue in the capture/input/encode paths would then be a root-level
+// RCE on the host instead of a user-level one. Also makes the daemon's
+// LOCAL_PEERCRED check correctly identify the agent as the console user,
+// not as root.
+//
+// Returns an error when the agent is running as a non-root uid that
+// differs from targetUID: non-root can only setuid to itself, so a
+// mismatch here means the spawn went to the wrong session.
+func dropAgentPrivileges(targetUID uint32) error {
+	if targetUID == 0 {
+		return fmt.Errorf("refusing to keep agent running as root (target uid 0)")
+	}
+	cur := uint32(os.Getuid())
+	if cur == targetUID {
+		return nil
+	}
+	if cur != 0 {
+		return fmt.Errorf("agent uid %d does not match expected %d and we lack root to fix it", cur, targetUID)
+	}
+	// Resolve the target user's real primary group rather than reusing
+	// targetUID as the gid: a user's primary group on macOS is typically
+	// staff(20), not gid==uid. Fail closed if the lookup fails.
+	targetGID, err := primaryGroupID(targetUID)
+	if err != nil {
+		return err
+	}
+	// Drop supplementary groups first: setgid alone doesn't touch the
+	// auxiliary group list, leaving root's groups attached would let the
+	// dropped process write to root-only group-writable files.
+	if err := syscall.Setgroups([]int{}); err != nil {
+		return fmt.Errorf("setgroups([]): %w", err)
+	}
+	if err := syscall.Setgid(targetGID); err != nil {
+		return fmt.Errorf("setgid(%d): %w", targetGID, err)
+	}
+	if os.Getgid() != targetGID || os.Getegid() != targetGID {
+		return fmt.Errorf("setgid verification: gid=%d egid=%d, expected %d", os.Getgid(), os.Getegid(), targetGID)
+	}
+	if err := syscall.Setuid(int(targetUID)); err != nil {
+		return fmt.Errorf("setuid(%d): %w", targetUID, err)
+	}
+	if uint32(os.Getuid()) != targetUID || uint32(os.Geteuid()) != targetUID {
+		return fmt.Errorf("setuid verification: uid=%d euid=%d, expected %d", os.Getuid(), os.Geteuid(), targetUID)
+	}
+	return nil
+}
+
+// primaryGroupID resolves the real primary group id of the user with the
+// given uid. Fails closed: a lookup or parse error returns an error so the
+// caller never falls back to using uid as the gid.
+func primaryGroupID(targetUID uint32) (int, error) {
+	u, err := user.LookupId(strconv.Itoa(int(targetUID)))
+	if err != nil {
+		return 0, fmt.Errorf("look up uid %d: %w", targetUID, err)
+	}
+	gid, err := strconv.Atoi(u.Gid)
+	if err != nil {
+		return 0, fmt.Errorf("parse gid %q for uid %d: %w", u.Gid, targetUID, err)
+	}
+	return gid, nil
+}