ipn,wgengine/magicsock: allow setting static node endpoints via tailscaled configfile (#12882)

wgengine/magicsock,ipn: allow setting static node endpoints via tailscaled config file.

Adds a new StaticEndpoints field to tailscaled config
that can be used to statically configure the endpoints
that the node advertizes. This field will replace
TS_DEBUG_PRETENDPOINTS env var that can be used to achieve the same.

Additionally adds some functionality that ensures that endpoints
are updated when configfile is reloaded.

Also, refactor configuring/reconfiguring components to use the
same functionality when configfile is parsed the first time or
subsequent times (after reload). Previously a configfile reload
did not result in resetting of prefs. Now it does- but does not yet
tell the relevant components to consume the new prefs. This is to
be done in a follow-up.

Updates tailscale/tailscale#12578


Signed-off-by: Irbe Krumina <irbe@tailscale.com>

ipn/conf.go

@@ -42,6 +42,10 @@ type ConfigVAlpha struct {
 	AutoUpdate      *AutoUpdatePrefs `json:",omitempty"`
 	ServeConfigTemp *ServeConfig     `json:",omitempty"` // TODO(bradfitz,maisem): make separate stable type for this
 
+	// StaticEndpoints are additional, user-defined endpoints that this node
+	// should advertise amongst its wireguard endpoints.
+	StaticEndpoints []netip.AddrPort `json:",omitempty"`
+
 	// TODO(bradfitz,maisem): future something like:
 	// Profile map[string]*Config // keyed by alice@gmail.com, corp.com (TailnetSID)
 }

ipn/ipnlocal/local.go

@@ -25,6 +25,7 @@
 	"os"
 	"os/exec"
 	"path/filepath"
+	"reflect"
 	"runtime"
 	"slices"
 	"sort"
@@ -391,18 +392,6 @@ func NewLocalBackend(logf logger.Logf, logID logid.PublicID, sys *tsd.System, lo
 		sds.SetDialer(dialer.SystemDial)
 	}
 
-	if sys.InitialConfig != nil {
-		p := pm.CurrentPrefs().AsStruct()
-		mp, err := sys.InitialConfig.Parsed.ToPrefs()
-		if err != nil {
-			return nil, err
-		}
-		p.ApplyEdits(&mp)
-		if err := pm.SetPrefs(p.View(), ipn.NetworkProfile{}); err != nil {
-			return nil, err
-		}
-	}
-
 	envknob.LogCurrent(logf)
 	osshare.SetFileSharingEnabled(false, logf)
 
@@ -417,7 +406,6 @@ func NewLocalBackend(logf logger.Logf, logID logid.PublicID, sys *tsd.System, lo
 		statsLogf:           logger.LogOnChange(logf, 5*time.Minute, clock.Now),
 		sys:                 sys,
 		health:              sys.HealthTracker(),
-		conf:                sys.InitialConfig,
 		e:                   e,
 		dialer:              dialer,
 		store:               store,
@@ -434,6 +422,12 @@ func NewLocalBackend(logf logger.Logf, logID logid.PublicID, sys *tsd.System, lo
 	}
 	mConn.SetNetInfoCallback(b.setNetInfo)
 
+	if sys.InitialConfig != nil {
+		if err := b.setConfigLocked(sys.InitialConfig); err != nil {
+			return nil, err
+		}
+	}
+
 	netMon := sys.NetMon.Get()
 	b.sockstatLogger, err = sockstatlog.NewLogger(logpolicy.LogsDir(logf), logf, logID, netMon, sys.HealthTracker())
 	if err != nil {
@@ -616,11 +610,50 @@ func (b *LocalBackend) ReloadConfig() (ok bool, err error) {
 	if err != nil {
 		return false, err
 	}
-	b.conf = conf
-	// TODO(bradfitz): apply things
+	if err := b.setConfigLocked(conf); err != nil {
+		return false, fmt.Errorf("error setting config: %w", err)
+	}
+
 	return true, nil
 }
 
+func (b *LocalBackend) setConfigLocked(conf *conffile.Config) error {
+
+	// TODO(irbekrm): notify the relevant components to consume any prefs
+	// updates. Currently only initial configfile settings are applied
+	// immediately.
+	p := b.pm.CurrentPrefs().AsStruct()
+	mp, err := conf.Parsed.ToPrefs()
+	if err != nil {
+		return fmt.Errorf("error parsing config to prefs: %w", err)
+	}
+	p.ApplyEdits(&mp)
+	if err := b.pm.SetPrefs(p.View(), ipn.NetworkProfile{}); err != nil {
+		return err
+	}
+
+	defer func() {
+		b.conf = conf
+	}()
+
+	if conf.Parsed.StaticEndpoints == nil && (b.conf == nil || b.conf.Parsed.StaticEndpoints == nil) {
+		return nil
+	}
+
+	// Ensure that magicsock conn has the up to date static wireguard
+	// endpoints. Setting the endpoints here triggers an asynchronous update
+	// of the node's advertised endpoints.
+	if b.conf == nil && len(conf.Parsed.StaticEndpoints) != 0 || !reflect.DeepEqual(conf.Parsed.StaticEndpoints, b.conf.Parsed.StaticEndpoints) {
+		ms, ok := b.sys.MagicSock.GetOK()
+		if !ok {
+			b.logf("[unexpected] ReloadConfig: MagicSock not set")
+		} else {
+			ms.SetStaticEndpoints(views.SliceOf(conf.Parsed.StaticEndpoints))
+		}
+	}
+	return nil
+}
+
 var assumeNetworkUpdateForTest = envknob.RegisterBool("TS_ASSUME_NETWORK_UP_FOR_TEST")
 
 // pauseOrResumeControlClientLocked pauses b.cc if there is no network available

wgengine/magicsock/magicsock.go

@@ -14,6 +14,7 @@
 	"io"
 	"net"
 	"net/netip"
+	"reflect"
 	"runtime"
 	"strconv"
 	"strings"
@@ -311,6 +312,12 @@ type Conn struct {
 	// lastEPERMRebind tracks the last time a rebind was performed
 	// after experiencing a syscall.EPERM.
 	lastEPERMRebind syncs.AtomicValue[time.Time]
+
+	// staticEndpoints are user set endpoints that this node should
+	// advertise amongst its wireguard endpoints. It is user's
+	// responsibility to ensure that traffic from these endpoints is routed
+	// to the node.
+	staticEndpoints views.Slice[netip.AddrPort]
 }
 
 // SetDebugLoggingEnabled controls whether spammy debug logging is enabled.
@@ -636,6 +643,22 @@ func (c *Conn) setEndpoints(endpoints []tailcfg.Endpoint) (changed bool) {
 	return true
 }
 
+// SetStaticEndpoints sets static endpoints to the provided value and triggers
+// an asynchronous update of the endpoints that this node advertises.
+// Static endpoints are endpoints explicitly configured by user.
+func (c *Conn) SetStaticEndpoints(ep views.Slice[netip.AddrPort]) {
+	c.mu.Lock()
+	if reflect.DeepEqual(c.staticEndpoints.AsSlice(), ep.AsSlice()) {
+		return
+	}
+	c.staticEndpoints = ep
+	c.mu.Unlock()
+	// Technically this is not a reSTUNning, but ReSTUN does what we need at
+	// this point- calls updateEndpoints or queues an update if there is
+	// already an in-progress update.
+	c.ReSTUN("static-endpoint-change")
+}
+
 // setNetInfoHavePortMap updates NetInfo.HavePortMap to true.
 func (c *Conn) setNetInfoHavePortMap() {
 	c.mu.Lock()
@@ -845,8 +868,10 @@ func (c *Conn) DiscoPublicKey() key.DiscoPublic {
 	return c.discoPublic
 }
 
-// determineEndpoints returns the machine's endpoint addresses. It
-// does a STUN lookup (via netcheck) to determine its public address.
+// determineEndpoints returns the machine's endpoint addresses. It does a STUN
+// lookup (via netcheck) to determine its public address. Additionally any
+// static enpoints provided by user are always added to the returned endpoints
+// without validating if the node can be reached via those endpoints.
 //
 // c.mu must NOT be held.
 func (c *Conn) determineEndpoints(ctx context.Context) ([]tailcfg.Endpoint, error) {
@@ -943,6 +968,10 @@ func (c *Conn) determineEndpoints(ctx context.Context) ([]tailcfg.Endpoint, erro
 	// re-run.
 	eps = c.endpointTracker.update(time.Now(), eps)
 
+	for i := range c.staticEndpoints.Len() {
+		addAddr(c.staticEndpoints.At(i), tailcfg.EndpointExplicitConf)
+	}
+
 	if localAddr := c.pconn4.LocalAddr(); localAddr.IP.IsUnspecified() {
 		ips, loopback, err := netmon.LocalAddresses()
 		if err != nil {
@@ -2359,6 +2388,8 @@ func (c *Conn) onPortMapChanged() { c.ReSTUN("portmap-changed") }
 
 // ReSTUN triggers an address discovery.
 // The provided why string is for debug logging only.
+// If Conn.staticEndpoints have been updated, calling ReSTUN will also result in
+// the new endpoints being advertised.
 func (c *Conn) ReSTUN(why string) {
 	c.mu.Lock()
 	defer c.mu.Unlock()