Authorize daemon IPC callers by their local identity

client/server/ssh_gate.go

@@ -0,0 +1,282 @@
+package server
+
+import (
+	"context"
+	"fmt"
+	"net/url"
+	"runtime"
+	"strings"
+
+	log "github.com/sirupsen/logrus"
+	"google.golang.org/genproto/googleapis/rpc/errdetails"
+	"google.golang.org/grpc/codes"
+	gstatus "google.golang.org/grpc/status"
+
+	"github.com/netbirdio/netbird/client/internal/daemonaddr"
+	"github.com/netbirdio/netbird/client/internal/ipcauth"
+	"github.com/netbirdio/netbird/client/internal/profilemanager"
+	"github.com/netbirdio/netbird/client/proto"
+	"github.com/netbirdio/netbird/util"
+)
+
+// The daemon runs as root/LocalSystem, so a handful of config changes cross the
+// user-to-root boundary and are restricted to privileged callers:
+//
+//   - Enabling SSH root login, or disabling SSH authentication, turns the
+//     daemon's SSH server into a root (or unauthenticated) shell.
+//   - Enabling the SSH server at all is what makes the above reachable, and a
+//     profile the caller owns is not a privilege they hold.
+//   - While the SSH server is enabled, repointing the profile at another
+//     management identity hands SSH authorization decisions, including which
+//     keys and users are accepted, to whoever controls that identity. Changing
+//     the management URL and deregistering the peer are both ways to do that.
+//
+// Everything else stays unauthenticated, so this is not an authorization model:
+// it only refuses the changes that would let a local user become root. A caller
+// whose identity cannot be established is refused as well.
+
+// privilegedConfigChange is the subset of a config request that crosses the
+// user-to-root boundary. Fields are nil or empty when the request leaves them
+// untouched.
+type privilegedConfigChange struct {
+	managementURL    string
+	serverSSHAllowed *bool
+	enableSSHRoot    *bool
+	disableSSHAuth   *bool
+}
+
+func privilegedChangeFromSetConfig(msg *proto.SetConfigRequest) privilegedConfigChange {
+	return privilegedConfigChange{
+		managementURL:    msg.GetManagementUrl(),
+		serverSSHAllowed: msg.ServerSSHAllowed,
+		enableSSHRoot:    msg.EnableSSHRoot,
+		disableSSHAuth:   msg.DisableSSHAuth,
+	}
+}
+
+func privilegedChangeFromLogin(msg *proto.LoginRequest) privilegedConfigChange {
+	return privilegedConfigChange{
+		managementURL:    msg.GetManagementUrl(),
+		serverSSHAllowed: msg.ServerSSHAllowed,
+		enableSSHRoot:    msg.EnableSSHRoot,
+		disableSSHAuth:   msg.DisableSSHAuth,
+	}
+}
+
+// requirePrivilegeForConfigChange refuses the privileged parts of a config
+// change when the caller is not root/administrator. stored is the profile's
+// current config, or nil when it has none yet.
+//
+// Each check compares against the stored value so that a request restating a
+// value it does not change is never refused: a UI that submits the whole
+// settings form must not start failing once an administrator has enabled SSH.
+func requirePrivilegeForConfigChange(ctx context.Context, stored *profilemanager.Config, change privilegedConfigChange) error {
+	if enables(storedFlag(stored, func(c *profilemanager.Config) *bool { return c.EnableSSHRoot }), change.enableSSHRoot) {
+		return denyPrivileged(ctx, "enabling SSH root login", ipcauth.UpCommand("--enable-ssh-root"))
+	}
+
+	if enables(storedFlag(stored, func(c *profilemanager.Config) *bool { return c.DisableSSHAuth }), change.disableSSHAuth) {
+		return denyPrivileged(ctx, "disabling SSH authentication", ipcauth.UpCommand("--disable-ssh-auth"))
+	}
+
+	if enables(sshServerCurrentlyAllowed(stored), change.serverSSHAllowed) {
+		return denyPrivileged(ctx, "enabling the NetBird SSH server", ipcauth.UpCommand("--allow-server-ssh"))
+	}
+
+	// Only guard the management binding while the SSH server is enabled: that is
+	// when the management identity decides who may open a shell here.
+	if !sshServerEnabled(stored) {
+		return nil
+	}
+
+	if change.managementURL != "" && !sameManagementURL(stored.ManagementURL, change.managementURL) {
+		return denyPrivileged(ctx,
+			"changing the management URL while the NetBird SSH server is enabled",
+			ipcauth.UpCommand("-m "+change.managementURL))
+	}
+
+	return nil
+}
+
+// requirePrivilegeForDeregistration refuses to deregister the peer from the
+// management server when the caller is not privileged and the profile has the
+// SSH server enabled. Deregistering frees the peer's key to be registered
+// against another management identity, which is the same handover the
+// management URL check refuses.
+//
+// Callers that treat deregistration as best-effort (profile removal) continue
+// without it; callers that were asked to deregister surface the error.
+func requirePrivilegeForDeregistration(ctx context.Context, cfg *profilemanager.Config) error {
+	if !sshServerEnabled(cfg) {
+		return nil
+	}
+
+	return denyPrivileged(ctx,
+		"deregistering this peer while the NetBird SSH server is enabled",
+		ipcauth.ElevatedCommand("netbird logout"))
+}
+
+// denyPrivileged returns nil when the caller is privileged, and otherwise a
+// PermissionDenied whose message names the action and the command that performs
+// it with the privileges it needs. The same summary and command ride along as an
+// ErrorInfo detail so the CLI and the UI can present them without parsing text.
+//
+// action reads as the subject of a sentence ("enabling SSH root login"), and
+// command is the equivalent command, already elevated for the platform.
+func denyPrivileged(ctx context.Context, action, command string) error {
+	id, ok := ipcauth.CallerIdentity(ctx)
+	if !ok {
+		log.Warnf("denying %s: the caller's identity cannot be verified on this control channel", action)
+		return privilegeError(unidentifiedSummary(action), reinstallCommand())
+	}
+
+	if ipcauth.IsPrivilegedCaller(id) {
+		log.Infof("allowing %s for privileged caller %s", action, id)
+		return nil
+	}
+
+	log.Warnf("denying %s for unprivileged caller %s", action, id)
+	actor, command := requiredActor(command)
+	return privilegeError(privilegeSummary(action, actor), command)
+}
+
+// requiredActor names who may perform the operation and adjusts the command to
+// match. A daemon that is not itself privileged delegates to its own identity, so
+// telling that host's user to become root is wrong twice over: root is not what the
+// daemon checks for, and a rootless container has neither root nor sudo.
+func requiredActor(command string) (string, string) {
+	self, delegates := ipcauth.SelfDelegatesTo()
+	if !delegates {
+		return ipcauth.PrivilegedActor(), command
+	}
+	return fmt.Sprintf("the user the daemon runs as (%s)", self), strings.ReplaceAll(command, "sudo ", "")
+}
+
+// privilegeError builds the PermissionDenied carrying summary and command.
+func privilegeError(summary, command string) error {
+	st := gstatus.New(codes.PermissionDenied, fmt.Sprintf("%s\n\n%s", summary, command))
+
+	detailed, err := st.WithDetails(&errdetails.ErrorInfo{
+		Reason: ipcauth.ErrorReasonPrivilegeRequired,
+		Domain: ipcauth.ErrorDomain,
+		Metadata: map[string]string{
+			ipcauth.ErrorMetaSummary: summary,
+			ipcauth.ErrorMetaCommand: command,
+		},
+	})
+	if err != nil {
+		log.Debugf("attach privilege error detail: %v", err)
+		return st.Err()
+	}
+	return detailed.Err()
+}
+
+// privilegeSummary states what is refused and what it needs, in one sentence
+// that reads the same in a dialog and in a terminal.
+func privilegeSummary(action, actor string) string {
+	return fmt.Sprintf("%s requires %s.", capitalize(action), actor)
+}
+
+// unidentifiedSummary covers a control channel that carries no caller identity.
+// Elevating does not help there, so it points at the daemon's socket instead.
+func unidentifiedSummary(action string) string {
+	return fmt.Sprintf("%s requires %s, and the daemon cannot verify who is calling over its current socket. "+
+		"Reinstall the service on a socket that carries the caller's identity.", capitalize(action), ipcauth.PrivilegedActor())
+}
+
+// reinstallCommand is the command that moves the daemon onto a socket whose
+// callers can be identified.
+func reinstallCommand() string {
+	if runtime.GOOS == "windows" {
+		return fmt.Sprintf("netbird service install --daemon-addr %s", daemonaddr.WindowsPipeAddr)
+	}
+	return "sudo netbird service install --daemon-addr unix:///var/run/netbird.sock"
+}
+
+func capitalize(s string) string {
+	if s == "" {
+		return s
+	}
+	return strings.ToUpper(s[:1]) + s[1:]
+}
+
+// enables reports whether requested turns a flag on that is currently off. A
+// request that restates the stored value, or turns the flag off, is not a
+// privileged change.
+func enables(stored, requested *bool) bool {
+	if requested == nil || !*requested {
+		return false
+	}
+	return stored == nil || !*stored
+}
+
+// storedFlag reads a flag from the stored config, tolerating a config that does
+// not exist yet.
+func storedFlag(cfg *profilemanager.Config, get func(*profilemanager.Config) *bool) *bool {
+	if cfg == nil {
+		return nil
+	}
+	return get(cfg)
+}
+
+// sshServerEnabled reports whether the profile currently runs the SSH server.
+//
+// A nil flag means ON, matching what the engine does with the same config
+// (util.ReturnBoolWithDefaultTrue in internal/connect.go, kept for configs written
+// before the flag existed). Reading it as OFF here would open the management-URL
+// and deregistration guards on exactly those legacy hosts, whose SSH server is
+// running. Configs loaded through profilemanager have already been materialised by
+// apply(), so this is the same answer by a route that does not depend on that.
+func sshServerEnabled(cfg *profilemanager.Config) bool {
+	if cfg == nil {
+		return false
+	}
+	return util.ReturnBoolWithDefaultTrue(cfg.ServerSSHAllowed)
+}
+
+// sshServerCurrentlyAllowed is the value an enable request is compared against. It
+// shares sshServerEnabled's nil-means-on default, so restating "on" for a legacy
+// config is correctly seen as no change.
+func sshServerCurrentlyAllowed(cfg *profilemanager.Config) *bool {
+	enabled := sshServerEnabled(cfg)
+	if cfg == nil {
+		return nil
+	}
+	return &enabled
+}
+
+// sameManagementURL reports whether requested addresses the same management
+// server as stored, comparing scheme, host and effective port so that an
+// equivalent spelling ("https://api.netbird.io" for a stored
+// "https://api.netbird.io:443") is not treated as a change. It fails closed:
+// anything unparseable counts as a change and therefore needs privilege.
+func sameManagementURL(stored *url.URL, requested string) bool {
+	if stored == nil {
+		return false
+	}
+
+	// Normalise the requested URL through the config layer's own parser, so the
+	// comparison cannot drift from how the value would actually be stored.
+	parsed, err := profilemanager.ParseServiceURL("Management URL", requested)
+	if err != nil {
+		return false
+	}
+
+	return stored.Scheme == parsed.Scheme &&
+		stored.Hostname() == parsed.Hostname() &&
+		effectivePort(stored) == effectivePort(parsed)
+}
+
+func effectivePort(u *url.URL) string {
+	if port := u.Port(); port != "" {
+		return port
+	}
+	switch u.Scheme {
+	case "https":
+		return "443"
+	case "http":
+		return "80"
+	default:
+		return ""
+	}
+}