auth, state: keep announced routes out of pending registrations

Routes are the one long list; the first MapRequest reports them.
A relogin keeps the node's own routes until then.

hscontrol/auth.go

@@ -392,24 +392,32 @@ func (h *Headscale) reqToNewRegisterResponse(
 }
 
 // registrationDataFromRequest builds the [types.RegistrationData] payload stored
-// in the auth cache for a pending registration. The original [tailcfg.Hostinfo] is
-// retained so that consumers (auth callback, observability) see the
-// fields the client originally announced; the bounded-LRU cap on the
-// cache is what bounds the unauthenticated cache-fill DoS surface.
+// in the auth cache for a pending registration. The [tailcfg.Hostinfo] is kept
+// so that consumers (auth callback, observability) see the fields the client
+// announced, except its routes: they are the one list a real client makes
+// long, and the node's first [tailcfg.MapRequest] reports them again.
 func registrationDataFromRequest(
 	req tailcfg.RegisterRequest,
 	machineKey key.MachinePublic,
 ) *types.RegistrationData {
-	var hostname string
+	var (
+		hostname string
+		hostinfo *tailcfg.Hostinfo
+	)
+
 	if req.Hostinfo != nil {
 		hostname = req.Hostinfo.Hostname
+
+		hi := *req.Hostinfo
+		hi.RoutableIPs = nil
+		hostinfo = &hi
 	}
 
 	regData := &types.RegistrationData{
 		MachineKey: machineKey,
 		NodeKey:    req.NodeKey,
 		Hostname:   hostname,
-		Hostinfo:   req.Hostinfo,
+		Hostinfo:   hostinfo,
 	}
 
 	if !req.Expiry.IsZero() {

hscontrol/auth_test.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"net/http"
+	"net/netip"
 	"net/url"
 	"strings"
 	"testing"
@@ -4599,3 +4600,34 @@ func TestRegisterRejectsUnencodableExpiry(t *testing.T) {
 	require.NoError(t, err)
 	assert.True(t, latest.Equal(*stored.Expiry))
 }
+
+// TestPendingRegistrationKeepsNoRoutes pins that a pending registration caches
+// the client's Hostinfo without its announced routes, the one list a client
+// makes long; the node's first MapRequest reports them again.
+func TestPendingRegistrationKeepsNoRoutes(t *testing.T) {
+	app := createTestApp(t)
+
+	hostinfo := &tailcfg.Hostinfo{
+		Hostname:    "pending-router",
+		OSVersion:   "6.12.0",
+		RoutableIPs: []netip.Prefix{netip.MustParsePrefix("10.0.0.0/24")},
+		Services:    []tailcfg.Service{{Proto: tailcfg.PeerAPI4, Port: 41641}},
+	}
+
+	resp, err := app.handleRegister(context.Background(), tailcfg.RegisterRequest{
+		NodeKey:  key.NewNode().Public(),
+		Hostinfo: hostinfo,
+	}, key.NewMachine().Public())
+	require.NoError(t, err)
+
+	authID, err := extractRegistrationIDFromAuthURL(resp.AuthURL)
+	require.NoError(t, err, "resp=%+v", resp)
+
+	entry, ok := app.state.GetAuthCacheEntry(authID)
+	require.True(t, ok)
+
+	want := hostinfo.Clone()
+	want.RoutableIPs = nil
+	assert.Equal(t, want, entry.RegistrationData().Hostinfo)
+	assert.Len(t, hostinfo.RoutableIPs, 1, "the request itself must be left alone")
+}

hscontrol/state/persist_test.go

@@ -2074,3 +2074,43 @@ func TestBootKeepsHostinfoTheMapPathStored(t *testing.T) {
 	osVersionLen := len(reloaded.Hostinfo().OSVersion())
 	assert.Equal(t, 60<<10, osVersionLen)
 }
+
+// TestReauthKeepsAnnouncedRoutes pins that an auth-path relogin keeps the
+// routes a router announced. Pending registrations carry none, and dropping
+// the node's own would withdraw its primary routes until the next MapRequest.
+func TestReauthKeepsAnnouncedRoutes(t *testing.T) {
+	_, s, nodeID := persistTestSetup(t)
+	t.Cleanup(func() { _ = s.Close() })
+
+	route := netip.MustParsePrefix("10.0.0.0/24")
+
+	node, ok := s.nodeStore.UpdateNode(nodeID, func(n *types.Node) {
+		n.Hostinfo = &tailcfg.Hostinfo{
+			Hostname: n.Hostname, RoutableIPs: []netip.Prefix{route},
+		}
+		n.ApprovedRoutes = []netip.Prefix{route}
+	})
+	require.True(t, ok)
+
+	_, epoch := s.Connect(nodeID)
+	require.NotZero(t, epoch)
+	require.Equal(t, []netip.Prefix{route}, s.GetNodePrimaryRoutes(nodeID),
+		"precondition: the node serves its route")
+
+	authID := types.MustAuthID()
+	s.SetAuthCacheEntry(authID, types.NewRegisterAuthRequest(&types.RegistrationData{
+		MachineKey: node.MachineKey(),
+		NodeKey:    key.NewNode().Public(),
+		Hostname:   node.Hostname(),
+		Hostinfo:   &tailcfg.Hostinfo{Hostname: node.Hostname()},
+	}))
+
+	relogged, _, err := s.HandleNodeFromAuthPath(
+		authID, node.TypedUserID(), nil, util.RegisterMethodOIDC,
+	)
+	require.NoError(t, err)
+	require.Equal(t, nodeID, relogged.ID(), "relogin must update the existing node")
+
+	assert.Equal(t, []netip.Prefix{route}, relogged.AnnouncedRoutes())
+	assert.Equal(t, []netip.Prefix{route}, s.GetNodePrimaryRoutes(nodeID))
+}

hscontrol/state/state.go

@@ -52,10 +52,9 @@ const (
 	registerCacheExpiration = time.Minute * 15
 
 	// defaultRegisterCacheMaxEntries is the default upper bound on the number
-	// of pending registration entries the auth cache will hold. With a 15-minute
-	// TTL and a stripped-down RegistrationData payload (~200 bytes per entry),
-	// 1024 entries cap the worst-case cache footprint at well under 1 MiB even
-	// under sustained unauthenticated cache-fill attempts.
+	// of pending registration entries the auth cache will hold. Each entry
+	// keeps a Hostinfo bounded at decode ([types.MaxHostinfoSize]) and
+	// without routes, so the entry cap bounds the cache's memory.
 	defaultRegisterCacheMaxEntries = 1024
 
 	// defaultNodeStoreBatchSize is the default number of write operations to batch
@@ -2244,6 +2243,10 @@ func (s *State) applyAuthNodeUpdate(params authNodeUpdateParams) (types.NodeView
 		node.DiscoKey = regData.DiscoKey
 		node.Hostname = params.Hostname
 
+		// Pending registrations do not cache announced routes; keep the
+		// node's own until its next MapRequest reports them.
+		routes := slices.Clone(node.AnnouncedRoutes())
+
 		// Preserve NetInfo from existing node when re-registering
 		node.Hostinfo = params.ValidHostinfo
 		node.Hostinfo.NetInfo = preserveNetInfo(
@@ -2251,6 +2254,7 @@ func (s *State) applyAuthNodeUpdate(params authNodeUpdateParams) (types.NodeView
 			params.ExistingNode.ID(),
 			params.ValidHostinfo,
 		)
+		node.Hostinfo.RoutableIPs = routes
 
 		// Preserve the node's live endpoints when the register request carried
 		// none. Web/OIDC relogins report endpoints via MapRequest, not register,

hscontrol/types/registration.go

@@ -13,11 +13,9 @@ import (
 // only the fields the registration callback path actually consumes when
 // promoting a pending registration to a real node.
 //
-// Combined with the bounded-LRU cache that holds these entries, this caps
-// the worst-case memory footprint of unauthenticated cache-fill attempts
-// at (max_entries × per_entry_size). The cache is sized so that the
-// product is bounded to a few MiB even with attacker-supplied 1 MiB
-// Hostinfos (the Noise body limit).
+// Any client can open a pending registration. The bounded-LRU cache that
+// holds these entries caps their number, and each entry stays small: its
+// Hostinfo is bounded at decode ([BoundHostinfo]) and kept without routes.
 type RegistrationData struct {
 	// MachineKey is the cryptographic identity of the machine being
 	// registered. Required.
@@ -34,11 +32,11 @@ type RegistrationData struct {
 	// Already validated/normalised by EnsureHostname at producer time.
 	Hostname string
 
-	// Hostinfo is the original [tailcfg.Hostinfo] from the [tailcfg.RegisterRequest],
-	// stored so that the auth callback can populate the new node's
-	// initial [tailcfg.Hostinfo] (and so that observability/CLI consumers see
-	// fields like OS, OSVersion, and IPNVersion before the first
-	// [tailcfg.MapRequest] restores the live set).
+	// Hostinfo is the [tailcfg.Hostinfo] from the [tailcfg.RegisterRequest]
+	// without its routes, stored so that the auth callback can populate the
+	// new node's initial [tailcfg.Hostinfo] (and so that observability/CLI
+	// consumers see fields like OS, OSVersion, and IPNVersion before the
+	// first [tailcfg.MapRequest] restores the live set, routes included).
 	//
 	// May be nil if the client did not send [tailcfg.Hostinfo] in the original
 	// [tailcfg.RegisterRequest].