all: implement lock revoke-keys command

The revoke-keys command allows nodes with tailnet lock keys
to collaborate to erase the use of a compromised key, and remove trust
in it.

Signed-off-by: Tom DNetto <tom@tailscale.com>
Updates ENG-1848

ipn/ipnlocal/network-lock.go

@@ -845,6 +845,93 @@ func (b *LocalBackend) NetworkLockAffectedSigs(keyID tkatype.KeyID) ([]tkatype.M
 	return resp.Signatures, nil
 }
 
+// NetworkLockGenerateRecoveryAUM generates an AUM which retroactively removes trust in the
+// specified keys. This AUM is signed by the current node and returned.
+//
+// If forkFrom is specified, it is used as the parent AUM to fork from. If the zero value,
+// the parent AUM is determined automatically.
+func (b *LocalBackend) NetworkLockGenerateRecoveryAUM(removeKeys []tkatype.KeyID, forkFrom tka.AUMHash) (*tka.AUM, error) {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	if b.tka == nil {
+		return nil, errNetworkLockNotActive
+	}
+	var nlPriv key.NLPrivate
+	if p := b.pm.CurrentPrefs(); p.Valid() && p.Persist().Valid() {
+		nlPriv = p.Persist().NetworkLockKey()
+	}
+	if nlPriv.IsZero() {
+		return nil, errMissingNetmap
+	}
+
+	aum, err := b.tka.authority.MakeRetroactiveRevocation(b.tka.storage, removeKeys, nlPriv.KeyID(), forkFrom)
+	if err != nil {
+		return nil, err
+	}
+
+	// Sign it ourselves.
+	aum.Signatures, err = nlPriv.SignAUM(aum.SigHash())
+	if err != nil {
+		return nil, fmt.Errorf("signing failed: %w", err)
+	}
+
+	return aum, nil
+}
+
+// NetworkLockCosignRecoveryAUM co-signs the provided recovery AUM and returns
+// the updated structure.
+//
+// The recovery AUM provided should be the output from a previous call to
+// NetworkLockGenerateRecoveryAUM or NetworkLockCosignRecoveryAUM.
+func (b *LocalBackend) NetworkLockCosignRecoveryAUM(aum *tka.AUM) (*tka.AUM, error) {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	if b.tka == nil {
+		return nil, errNetworkLockNotActive
+	}
+	var nlPriv key.NLPrivate
+	if p := b.pm.CurrentPrefs(); p.Valid() && p.Persist().Valid() {
+		nlPriv = p.Persist().NetworkLockKey()
+	}
+	if nlPriv.IsZero() {
+		return nil, errMissingNetmap
+	}
+	for _, sig := range aum.Signatures {
+		if bytes.Equal(sig.KeyID, nlPriv.KeyID()) {
+			return nil, errors.New("this node has already signed this recovery AUM")
+		}
+	}
+
+	// Sign it ourselves.
+	sigs, err := nlPriv.SignAUM(aum.SigHash())
+	if err != nil {
+		return nil, fmt.Errorf("signing failed: %w", err)
+	}
+	aum.Signatures = append(aum.Signatures, sigs...)
+
+	return aum, nil
+}
+
+func (b *LocalBackend) NetworkLockSubmitRecoveryAUM(aum *tka.AUM) error {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	if b.tka == nil {
+		return errNetworkLockNotActive
+	}
+	var ourNodeKey key.NodePublic
+	if p := b.pm.CurrentPrefs(); p.Valid() && p.Persist().Valid() && !p.Persist().PrivateNodeKey().IsZero() {
+		ourNodeKey = p.Persist().PublicNodeKey()
+	}
+	if ourNodeKey.IsZero() {
+		return errors.New("no node-key: is tailscale logged in?")
+	}
+
+	b.mu.Unlock()
+	_, err := b.tkaDoSyncSend(ourNodeKey, aum.Hash(), []tka.AUM{*aum}, false)
+	b.mu.Lock()
+	return err
+}
+
 var tkaSuffixEncoder = base64.RawStdEncoding
 
 // NetworkLockWrapPreauthKey wraps a pre-auth key with information to

ipn/ipnlocal/network-lock_test.go

@@ -994,3 +994,129 @@ func TestTKAAffectedSigs(t *testing.T) {
 		})
 	}
 }
+
+func TestTKARecoverCompromisedKeyFlow(t *testing.T) {
+	nodePriv := key.NewNode()
+	nlPriv := key.NewNLPrivate()
+	cosignPriv := key.NewNLPrivate()
+	compromisedPriv := key.NewNLPrivate()
+
+	pm := must.Get(newProfileManager(new(mem.Store), t.Logf))
+	must.Do(pm.SetPrefs((&ipn.Prefs{
+		Persist: &persist.Persist{
+			PrivateNodeKey: nodePriv,
+			NetworkLockKey: nlPriv,
+		},
+	}).View()))
+
+	// Make a fake TKA authority, to seed local state.
+	disablementSecret := bytes.Repeat([]byte{0xa5}, 32)
+	key := tka.Key{Kind: tka.Key25519, Public: nlPriv.Public().Verifier(), Votes: 2}
+	cosignKey := tka.Key{Kind: tka.Key25519, Public: cosignPriv.Public().Verifier(), Votes: 2}
+	compromisedKey := tka.Key{Kind: tka.Key25519, Public: compromisedPriv.Public().Verifier(), Votes: 1}
+
+	temp := t.TempDir()
+	tkaPath := filepath.Join(temp, "tka-profile", string(pm.CurrentProfile().ID))
+	os.Mkdir(tkaPath, 0755)
+	chonk, err := tka.ChonkDir(tkaPath)
+	if err != nil {
+		t.Fatal(err)
+	}
+	authority, _, err := tka.Create(chonk, tka.State{
+		Keys:               []tka.Key{key, compromisedKey, cosignKey},
+		DisablementSecrets: [][]byte{tka.DisablementKDF(disablementSecret)},
+	}, nlPriv)
+	if err != nil {
+		t.Fatalf("tka.Create() failed: %v", err)
+	}
+
+	ts, client := fakeNoiseServer(t, http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		defer r.Body.Close()
+		switch r.URL.Path {
+		case "/machine/tka/sync/send":
+			body := new(tailcfg.TKASyncSendRequest)
+			if err := json.NewDecoder(r.Body).Decode(body); err != nil {
+				t.Fatal(err)
+			}
+			t.Logf("got sync send:\n%+v", body)
+
+			var remoteHead tka.AUMHash
+			if err := remoteHead.UnmarshalText([]byte(body.Head)); err != nil {
+				t.Fatalf("head unmarshal: %v", err)
+			}
+			toApply := make([]tka.AUM, len(body.MissingAUMs))
+			for i, a := range body.MissingAUMs {
+				if err := toApply[i].Unserialize(a); err != nil {
+					t.Fatalf("decoding missingAUM[%d]: %v", i, err)
+				}
+			}
+
+			// Apply the recovery AUM to an authority to make sure it works.
+			if err := authority.Inform(chonk, toApply); err != nil {
+				t.Errorf("recovery AUM could not be applied: %v", err)
+			}
+			// Make sure the key we removed isn't trusted.
+			if authority.KeyTrusted(compromisedPriv.KeyID()) {
+				t.Error("compromised key was not removed from tka")
+			}
+
+			w.WriteHeader(200)
+			if err := json.NewEncoder(w).Encode(tailcfg.TKASubmitSignatureResponse{}); err != nil {
+				t.Fatal(err)
+			}
+
+		default:
+			t.Errorf("unhandled endpoint path: %v", r.URL.Path)
+			w.WriteHeader(404)
+		}
+	}))
+	defer ts.Close()
+	cc := fakeControlClient(t, client)
+	b := LocalBackend{
+		varRoot: temp,
+		cc:      cc,
+		ccAuto:  cc,
+		logf:    t.Logf,
+		tka: &tkaState{
+			authority: authority,
+			storage:   chonk,
+		},
+		pm:    pm,
+		store: pm.Store(),
+	}
+
+	aum, err := b.NetworkLockGenerateRecoveryAUM([]tkatype.KeyID{compromisedPriv.KeyID()}, tka.AUMHash{})
+	if err != nil {
+		t.Fatalf("NetworkLockGenerateRecoveryAUM() failed: %v", err)
+	}
+
+	// Cosign using the cosigning key.
+	{
+		pm := must.Get(newProfileManager(new(mem.Store), t.Logf))
+		must.Do(pm.SetPrefs((&ipn.Prefs{
+			Persist: &persist.Persist{
+				PrivateNodeKey: nodePriv,
+				NetworkLockKey: cosignPriv,
+			},
+		}).View()))
+		b := LocalBackend{
+			varRoot: temp,
+			logf:    t.Logf,
+			tka: &tkaState{
+				authority: authority,
+				storage:   chonk,
+			},
+			pm:    pm,
+			store: pm.Store(),
+		}
+		if aum, err = b.NetworkLockCosignRecoveryAUM(aum); err != nil {
+			t.Fatalf("NetworkLockCosignRecoveryAUM() failed: %v", err)
+		}
+	}
+
+	// Finally, submit the recovery AUM. Validation is done
+	// in the fake control handler.
+	if err := b.NetworkLockSubmitRecoveryAUM(aum); err != nil {
+		t.Errorf("NetworkLockSubmitRecoveryAUM() failed: %v", err)
+	}
+}