control/controlclient, tailcfg: add Node.Expired field, set for expired nodes

Nodes that are expired, taking into account the time delta calculated
from MapResponse.ControlTime have the newly-added Expired boolean set.
For additional defense-in-depth, also replicate what control does and
clear the Endpoints and DERP fields, and additionally set the node key
to a bogus value.

Updates #6932

Signed-off-by: Andrew Dunham <andrew@du.nham.ca>
Change-Id: Ia2bd6b56064416feee28aef5699ca7090940662a

control/controlclient/map.go

@@ -9,6 +9,7 @@ import (
 	"log"
 	"net/netip"
 	"sort"
+	"time"
 
 	"tailscale.com/envknob"
 	"tailscale.com/tailcfg"
@@ -52,6 +53,12 @@ type mapSession struct {
 	lastPopBrowserURL      string
 	stickyDebug            tailcfg.Debug // accumulated opt.Bool values
 	lastTKAInfo            *tailcfg.TKAInfo
+	previouslyExpired      map[tailcfg.StableNodeID]bool // to avoid log spam
+
+	// clockDelta stores the delta between the current time and the time
+	// received from control such that:
+	//    time.Now().Add(clockDelta) == MapResponse.ControlTime
+	clockDelta time.Duration
 
 	// netMapBuilding is non-nil during a netmapForResponse call,
 	// containing the value to be returned, once fully populated.
@@ -60,11 +67,12 @@ type mapSession struct {
 
 func newMapSession(privateNodeKey key.NodePrivate) *mapSession {
 	ms := &mapSession{
-		privateNodeKey:  privateNodeKey,
-		logf:            logger.Discard,
-		vlogf:           logger.Discard,
-		lastDNSConfig:   new(tailcfg.DNSConfig),
-		lastUserProfile: map[tailcfg.UserID]tailcfg.UserProfile{},
+		privateNodeKey:    privateNodeKey,
+		logf:              logger.Discard,
+		vlogf:             logger.Discard,
+		lastDNSConfig:     new(tailcfg.DNSConfig),
+		lastUserProfile:   map[tailcfg.UserID]tailcfg.UserProfile{},
+		previouslyExpired: map[tailcfg.StableNodeID]bool{},
 	}
 	return ms
 }
@@ -85,6 +93,7 @@ func (ms *mapSession) addUserProfile(userID tailcfg.UserID) {
 // information from prior MapResponse values.
 func (ms *mapSession) netmapForResponse(resp *tailcfg.MapResponse) *netmap.NetworkMap {
 	undeltaPeers(resp, ms.previousPeers)
+	ms.flagExpiredPeers(resp)
 
 	ms.previousPeers = cloneNodes(resp.Peers) // defensive/lazy clone, since this escapes to who knows where
 	for _, up := range resp.UserProfiles {
@@ -343,6 +352,83 @@ func undeltaPeers(mapRes *tailcfg.MapResponse, prev []*tailcfg.Node) {
 	mapRes.PeersRemoved = nil
 }
 
+// For extra defense-in-depth, when we're testing expired nodes we check
+// ControlTime against this 'epoch' (set to the approximate time that this code
+// was written) such that if control (or Headscale, etc.) sends a ControlTime
+// that's sufficiently far in the past, we can safely ignore it.
+var flagExpiredPeersEpoch = time.Unix(1673373066, 0)
+
+// If the offset between the current time and the time received from control is
+// larger than this, we store an offset in our mapSession to adjust future
+// clock timings.
+const minClockDelta = 1 * time.Minute
+
+// flagExpiredPeers updates mapRes.Peers, mutating all peers that have expired,
+// taking into account any clock skew detected by using the ControlTime field
+// in the MapResponse. We don't actually remove expired peers from the Peers
+// array; instead, we clear some fields of the Node object, and set
+// Node.Expired so other parts of the codebase can provide more clear error
+// messages when attempting to e.g. ping an expired node.
+//
+// This is additionally a defense-in-depth against something going wrong with
+// control such that we start seeing expired peers with a valid Endpoints or
+// DERP field.
+func (ms *mapSession) flagExpiredPeers(mapRes *tailcfg.MapResponse) {
+	localNow := clockNow()
+
+	// If we have a ControlTime field, update our delta.
+	if mapRes.ControlTime != nil && !mapRes.ControlTime.IsZero() {
+		delta := mapRes.ControlTime.Sub(localNow)
+		if delta.Abs() > minClockDelta {
+			ms.logf("[v1] netmap: flagExpiredPeers: setting clock delta to %v", delta)
+			ms.clockDelta = delta
+		} else {
+			ms.clockDelta = 0
+		}
+	}
+
+	// Adjust our current time by any saved delta to adjust for clock skew.
+	controlNow := localNow.Add(ms.clockDelta)
+	if controlNow.Before(flagExpiredPeersEpoch) {
+		ms.logf("netmap: flagExpiredPeers: [unexpected] delta-adjusted current time is before hardcoded epoch; skipping")
+		return
+	}
+
+	for _, peer := range mapRes.Peers {
+		// Nodes that don't expire have KeyExpiry set to the zero time;
+		// skip those and peers that are already marked as expired
+		// (e.g. from control).
+		if peer.KeyExpiry.IsZero() || peer.KeyExpiry.After(controlNow) {
+			delete(ms.previouslyExpired, peer.StableID)
+			continue
+		} else if peer.Expired {
+			continue
+		}
+
+		if !ms.previouslyExpired[peer.StableID] {
+			ms.logf("[v1] netmap: flagExpiredPeers: clearing expired peer %v", peer.StableID)
+			ms.previouslyExpired[peer.StableID] = true
+		}
+
+		// Actually mark the node as expired
+		peer.Expired = true
+
+		// Control clears the Endpoints and DERP fields of expired
+		// nodes; do so here as well. The Expired bool is the correct
+		// thing to set, but this replicates the previous behaviour.
+		//
+		// NOTE: this is insufficient to actually break connectivity,
+		// since we discover endpoints via DERP, and due to DERP return
+		// path optimization.
+		peer.Endpoints = nil
+		peer.DERP = ""
+
+		// Defense-in-depth: break the node's public key as well, in
+		// case something tries to communicate.
+		peer.Key = key.NodePublicWithBadOldPrefix(peer.Key)
+	}
+}
+
 // ptrCopy returns a pointer to a newly allocated shallow copy of *v.
 func ptrCopy[T any](v *T) *T {
 	if v == nil {

control/controlclient/map_test.go

@@ -308,26 +308,141 @@ func TestUndeltaPeers(t *testing.T) {
 	}
 }
 
+func TestFlagExpiredPeers(t *testing.T) {
+	n := func(id tailcfg.NodeID, name string, expiry time.Time, mod ...func(*tailcfg.Node)) *tailcfg.Node {
+		n := &tailcfg.Node{ID: id, Name: name, KeyExpiry: expiry}
+		for _, f := range mod {
+			f(n)
+		}
+		return n
+	}
+
+	now := time.Unix(1673373129, 0)
+
+	oldClockNow := clockNow
+	clockNow = func() time.Time { return now }
+	t.Cleanup(func() { clockNow = oldClockNow })
+
+	timeInPast := now.Add(-1 * time.Hour)
+	timeInFuture := now.Add(1 * time.Hour)
+
+	timeBeforeEpoch := flagExpiredPeersEpoch.Add(-1 * time.Second)
+	if now.Before(timeBeforeEpoch) {
+		panic("current time in test cannot be before epoch")
+	}
+
+	var expiredKey key.NodePublic
+	if err := expiredKey.UnmarshalText([]byte("nodekey:6da774d5d7740000000000000000000000000000000000000000000000000000")); err != nil {
+		panic(err)
+	}
+
+	tests := []struct {
+		name   string
+		mapRes *tailcfg.MapResponse
+		want   []*tailcfg.Node
+	}{
+		{
+			name: "no_expiry",
+			mapRes: &tailcfg.MapResponse{
+				ControlTime: &now,
+				Peers: []*tailcfg.Node{
+					n(1, "foo", timeInFuture),
+					n(2, "bar", timeInFuture),
+				},
+			},
+			want: []*tailcfg.Node{
+				n(1, "foo", timeInFuture),
+				n(2, "bar", timeInFuture),
+			},
+		},
+		{
+			name: "expiry",
+			mapRes: &tailcfg.MapResponse{
+				ControlTime: &now,
+				Peers: []*tailcfg.Node{
+					n(1, "foo", timeInFuture),
+					n(2, "bar", timeInPast),
+				},
+			},
+			want: []*tailcfg.Node{
+				n(1, "foo", timeInFuture),
+				n(2, "bar", timeInPast, func(n *tailcfg.Node) {
+					n.Expired = true
+					n.Key = expiredKey
+				}),
+			},
+		},
+		{
+			name: "bad_ControlTime",
+			mapRes: &tailcfg.MapResponse{
+				// ControlTime here is intentionally before our hardcoded epoch
+				ControlTime: &timeBeforeEpoch,
+
+				Peers: []*tailcfg.Node{
+					n(1, "foo", timeInFuture),
+					n(2, "bar", timeBeforeEpoch.Add(-1*time.Hour)), // before ControlTime
+				},
+			},
+			want: []*tailcfg.Node{
+				n(1, "foo", timeInFuture),
+				n(2, "bar", timeBeforeEpoch.Add(-1*time.Hour)), // should have expired, but ControlTime is before epoch
+			},
+		},
+		{
+			name: "tagged_node",
+			mapRes: &tailcfg.MapResponse{
+				ControlTime: &now,
+				Peers: []*tailcfg.Node{
+					n(1, "foo", timeInFuture),
+					n(2, "bar", time.Time{}), // tagged node; zero expiry
+				},
+			},
+			want: []*tailcfg.Node{
+				n(1, "foo", timeInFuture),
+				n(2, "bar", time.Time{}), // not expired
+			},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			ms := newTestMapSession(t)
+			ms.flagExpiredPeers(tt.mapRes)
+			if !reflect.DeepEqual(tt.mapRes.Peers, tt.want) {
+				t.Errorf("wrong results\n got: %s\nwant: %s", formatNodes(tt.mapRes.Peers), formatNodes(tt.want))
+			}
+		})
+	}
+}
+
 func formatNodes(nodes []*tailcfg.Node) string {
 	var sb strings.Builder
 	for i, n := range nodes {
 		if i > 0 {
 			sb.WriteString(", ")
 		}
-		var extra string
+		fmt.Fprintf(&sb, "(%d, %q", n.ID, n.Name)
+
 		if n.Online != nil {
-			extra += fmt.Sprintf(", online=%v", *n.Online)
+			fmt.Fprintf(&sb, ", online=%v", *n.Online)
 		}
 		if n.LastSeen != nil {
-			extra += fmt.Sprintf(", lastSeen=%v", n.LastSeen.Unix())
+			fmt.Fprintf(&sb, ", lastSeen=%v", n.LastSeen.Unix())
 		}
-		fmt.Fprintf(&sb, "(%d, %q%s)", n.ID, n.Name, extra)
+		if n.Key != (key.NodePublic{}) {
+			fmt.Fprintf(&sb, ", key=%v", n.Key.String())
+		}
+		if n.Expired {
+			fmt.Fprintf(&sb, ", expired=true")
+		}
+		sb.WriteString(")")
 	}
 	return sb.String()
 }
 
 func newTestMapSession(t *testing.T) *mapSession {
-	return newMapSession(key.NewNode())
+	ms := newMapSession(key.NewNode())
+	ms.logf = t.Logf
+	return ms
 }
 
 func TestNetmapForResponse(t *testing.T) {

tailcfg/tailcfg.go

@@ -255,6 +255,12 @@ type Node struct {
 
 	// DataPlaneAuditLogID is the per-node logtail ID used for data plane audit logging.
 	DataPlaneAuditLogID string `json:",omitempty"`
+
+	// Expired is whether this node's key has expired. Control may send
+	// this; clients are only allowed to set this from false to true. On
+	// the client, this is calculated client-side based on a timestamp sent
+	// from control, to avoid clock skew issues.
+	Expired bool `json:",omitempty"`
 }
 
 // DisplayName returns the user-facing name for a node which should
@@ -1628,7 +1634,8 @@ func (n *Node) Equal(n2 *Node) bool {
 		n.ComputedName == n2.ComputedName &&
 		n.computedHostIfDifferent == n2.computedHostIfDifferent &&
 		n.ComputedNameWithHost == n2.ComputedNameWithHost &&
-		eqStrings(n.Tags, n2.Tags)
+		eqStrings(n.Tags, n2.Tags) &&
+		n.Expired == n2.Expired
 }
 
 func eqBoolPtr(a, b *bool) bool {

tailcfg/tailcfg_clone.go

@@ -97,6 +97,7 @@ var _NodeCloneNeedsRegeneration = Node(struct {
 	computedHostIfDifferent string
 	ComputedNameWithHost    string
 	DataPlaneAuditLogID     string
+	Expired                 bool
 }{})
 
 // Clone makes a deep copy of Hostinfo.

tailcfg/tailcfg_test.go

@@ -334,7 +334,7 @@ func TestNodeEqual(t *testing.T) {
 		"Capabilities",
 		"UnsignedPeerAPIOnly",
 		"ComputedName", "computedHostIfDifferent", "ComputedNameWithHost",
-		"DataPlaneAuditLogID",
+		"DataPlaneAuditLogID", "Expired",
 	}
 	if have := fieldsOf(reflect.TypeOf(Node{})); !reflect.DeepEqual(have, nodeHandles) {
 		t.Errorf("Node.Equal check might be out of sync\nfields: %q\nhandled: %q\n",
@@ -514,6 +514,11 @@ func TestNodeEqual(t *testing.T) {
 			&Node{},
 			false,
 		},
+		{
+			&Node{Expired: true},
+			&Node{},
+			false,
+		},
 	}
 	for i, tt := range tests {
 		got := tt.a.Equal(tt.b)

tailcfg/tailcfg_view.go

@@ -175,6 +175,7 @@ func (v NodeView) UnsignedPeerAPIOnly() bool         { return v.ж.UnsignedPeerA
 func (v NodeView) ComputedName() string              { return v.ж.ComputedName }
 func (v NodeView) ComputedNameWithHost() string      { return v.ж.ComputedNameWithHost }
 func (v NodeView) DataPlaneAuditLogID() string       { return v.ж.DataPlaneAuditLogID }
+func (v NodeView) Expired() bool                     { return v.ж.Expired }
 func (v NodeView) Equal(v2 NodeView) bool            { return v.ж.Equal(v2.ж) }
 
 // A compilation failure here means this code must be regenerated, with the command at the top of this file.
@@ -207,6 +208,7 @@ var _NodeViewNeedsRegeneration = Node(struct {
 	computedHostIfDifferent string
 	ComputedNameWithHost    string
 	DataPlaneAuditLogID     string
+	Expired                 bool
 }{})
 
 // View returns a readonly view of Hostinfo.

types/key/node.go

@@ -193,6 +193,23 @@ func NodePublicFromRaw32(raw mem.RO) NodePublic {
 	return ret
 }
 
+// badOldPrefix is a nodekey/discokey prefix that, when base64'd, serializes
+// with a "bad01" ("bad ol'", ~"bad old") prefix. It's used for expired node
+// keys so when we debug a customer issue, the "bad01" can jump out to us. See:
+//
+//	https://github.com/tailscale/tailscale/issues/6932
+var badOldPrefix = []byte{109, 167, 116, 213, 215, 116}
+
+// NodePublicWithBadOldPrefix returns a copy of k with its leading public key
+// bytes mutated such that it base64's to a ShortString of [bad01] ("bad ol'"
+// [expired node key]).
+func NodePublicWithBadOldPrefix(k NodePublic) NodePublic {
+	var buf [32]byte
+	k.AppendTo(buf[:0])
+	copy(buf[:], badOldPrefix)
+	return NodePublicFromRaw32(mem.B(buf[:]))
+}
+
 // IsZero reports whether k is the zero value.
 func (k NodePublic) IsZero() bool {
 	return k == NodePublic{}

util/deephash/deephash_test.go

@@ -576,7 +576,7 @@ func TestGetTypeHasher(t *testing.T) {
 		{
 			name: "tailcfg.Node",
 			val:  &tailcfg.Node{},
-			out:  "\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\tn\x88\xf1\xff\xff\xff\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\tn\x88\xf1\xff\xff\xff\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00",
+			out:  "\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\tn\x88\xf1\xff\xff\xff\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\tn\x88\xf1\xff\xff\xff\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00",
 		},
 	}
 	for _, tt := range tests {