server: log bcrypt cost if > 12, error on runtime > 10s

The bcrypt hashing algorithm runtime grows exponentially with cost,
and might cause a timeout if the cost is too high. Notifying the user
of high cost and of long running calculations will help with tuning
and debugging.

server/api.go

@@ -21,6 +21,9 @@ import (
 // to determine if the server supports specific features.
 const apiVersion = 2
 
+// recCost is the recommended bcrypt cost, which balances hash strength and time
+const recCost = 12
+
 // NewAPI returns a server which implements the gRPC API interface.
 func NewAPI(s storage.Storage, logger logrus.FieldLogger) api.DexServer {
 	return dexAPI{
@@ -80,16 +83,16 @@ func (d dexAPI) DeleteClient(ctx context.Context, req *api.DeleteClientReq) (*ap
 	return &api.DeleteClientResp{}, nil
 }
 
-// checkCost returns an error if the hash provided does not meet minimum cost requirement
-func checkCost(hash []byte) error {
+// checkCost returns an error if the hash provided does not meet minimum cost requirement, and the actual bcrypt cost
+func checkCost(hash []byte) (int, error) {
 	actual, err := bcrypt.Cost(hash)
 	if err != nil {
-		return fmt.Errorf("parsing bcrypt hash: %v", err)
+		return 0, fmt.Errorf("parsing bcrypt hash: %v", err)
 	}
 	if actual < bcrypt.DefaultCost {
-		return fmt.Errorf("given hash cost = %d, does not meet minimum cost requirement = %d", actual, bcrypt.DefaultCost)
+		return actual, fmt.Errorf("given hash cost = %d, does not meet minimum cost requirement = %d", actual, bcrypt.DefaultCost)
 	}
-	return nil
+	return actual, nil
 }
 
 func (d dexAPI) CreatePassword(ctx context.Context, req *api.CreatePasswordReq) (*api.CreatePasswordResp, error) {
@@ -100,9 +103,13 @@ func (d dexAPI) CreatePassword(ctx context.Context, req *api.CreatePasswordReq)
 		return nil, errors.New("no user ID supplied")
 	}
 	if req.Password.Hash != nil {
-		if err := checkCost(req.Password.Hash); err != nil {
+		cost, err := checkCost(req.Password.Hash)
+		if err != nil {
 			return nil, err
 		}
+		if cost > recCost {
+			d.logger.Warnln("bcrypt cost = %d, password encryption might timeout. Recommended bcrypt cost is 12", cost)
+		}
 	} else {
 		return nil, errors.New("no hash of password supplied")
 	}
@@ -133,9 +140,13 @@ func (d dexAPI) UpdatePassword(ctx context.Context, req *api.UpdatePasswordReq)
 	}
 
 	if req.NewHash != nil {
-		if err := checkCost(req.NewHash); err != nil {
+		cost, err := checkCost(req.NewHash)
+		if err != nil {
 			return nil, err
 		}
+		if cost > recCost {
+			d.logger.Warnln("bcrypt cost = %d, password encryption might timeout. Recommended bcrypt cost is 12", cost)
+		}
 	}
 
 	updater := func(old storage.Password) (storage.Password, error) {

server/api_test.go

@@ -119,6 +119,69 @@ func TestPassword(t *testing.T) {
 
 }
 
+// Ensures checkCost returns expected values
+func TestCheckCost(t *testing.T) {
+	logger := &logrus.Logger{
+		Out:       os.Stderr,
+		Formatter: &logrus.TextFormatter{DisableColors: true},
+		Level:     logrus.DebugLevel,
+	}
+
+	s := memory.New(logger)
+	client := newAPI(s, logger, t)
+	defer client.Close()
+
+	tests := []struct {
+		name         string
+		inputHash    []byte
+		expectedCost int
+		wantErr      bool
+	}{
+		{
+			name: "valid cost",
+			// bcrypt hash of the value "test1" with cost 12
+			inputHash:    []byte("$2a$12$M2Ot95Qty1MuQdubh1acWOiYadJDzeVg3ve4n5b.dgcgPdjCseKx2"),
+			expectedCost: recCost,
+		},
+		{
+			name:      "invalid hash",
+			inputHash: []byte(""),
+			wantErr:   true,
+		},
+		{
+			name: "cost below default",
+			// bcrypt hash of the value "test1" with cost 4
+			inputHash: []byte("$2a$04$8bSTbuVCLpKzaqB3BmgI7edDigG5tIQKkjYUu/mEO9gQgIkw9m7eG"),
+			wantErr:   true,
+		},
+		{
+			name: "cost above recommendation",
+			// bcrypt hash of the value "test1" with cost 20
+			inputHash:    []byte("$2a$20$yODn5quqK9MZdePqYLs6Y.Jr4cOO1P0aXsKz0eTa2rxOmu8e7ETpi"),
+			expectedCost: 20,
+		},
+	}
+
+	for _, tc := range tests {
+		cost, err := checkCost(tc.inputHash)
+		if err != nil {
+			if !tc.wantErr {
+				t.Errorf("%s: %s", tc.name, err)
+			}
+			continue
+		}
+
+		if tc.wantErr {
+			t.Errorf("%s: expected err", tc.name)
+			continue
+		}
+
+		if cost != tc.expectedCost {
+			t.Errorf("%s: exepcted cost = %d but got cost = %d", tc.name, tc.expectedCost, cost)
+		}
+	}
+}
+
 // Attempts to list and revoke an exisiting refresh token.
 func TestRefreshToken(t *testing.T) {
 	logger := &logrus.Logger{

server/server.go

@@ -288,9 +288,25 @@ func (db passwordDB) Login(ctx context.Context, s connector.Scopes, email, passw
 		}
 		return connector.Identity{}, false, nil
 	}
-	if err := bcrypt.CompareHashAndPassword(p.Hash, []byte(password)); err != nil {
+
+	// Return an error if password-hash comparison takes longer than 10 seconds
+	errCh := make(chan error, 1)
+	go func() {
+		errCh <- bcrypt.CompareHashAndPassword(p.Hash, []byte(password))
+	}()
+	select {
+	case err = <-errCh:
+		if err != nil {
 			return connector.Identity{}, false, nil
 		}
+	case <-time.After(time.Second * 10):
+		var cost int
+		if cost, err = bcrypt.Cost(p.Hash); err == nil {
+			err = fmt.Errorf("password-hash comparison timeout: your bcrypt cost = %d, recommended cost = %d", cost, recCost)
+		}
+		return connector.Identity{}, false, err
+	}
+
 	return connector.Identity{
 		UserID:        p.UserID,
 		Username:      p.Username,

server/server_test.go

@@ -896,6 +896,116 @@ func TestPasswordDB(t *testing.T) {
 
 }
 
+// A warning message should be logged if password-hash comparison takes longer than 10s
+func TestLoginTimeout(t *testing.T) {
+	s := memory.New(logger)
+	conn := newPasswordDB(s)
+
+	pw := "test1"
+
+	tests := []struct {
+		name, email, password string
+		pwHash                []byte
+		wantIdentity          connector.Identity
+		wantInvalid           bool
+		wantedErr             string
+	}{
+		{
+			name:     "valid password min cost",
+			email:    "jane@example.com",
+			password: pw,
+			// bcrypt hash of the value "test1" with cost 4
+			pwHash: []byte("$2a$04$lGqOe5gnlpsfreQ1OJHxGOO7f5FyyESyICkswSFATM1cnBVgCyyuG"),
+			wantIdentity: connector.Identity{
+				Email:         "jane@example.com",
+				Username:      "jane",
+				UserID:        "foobar",
+				EmailVerified: true,
+			},
+		},
+		{
+			name:     "valid password reccomended cost",
+			email:    "jane@example.com",
+			password: pw,
+			// bcrypt hash of the value "test1" with cost 12
+			pwHash: []byte("$2a$12$VZNNjuCUGX2NG5S1ci.3Ku9mI9DmA9XeXyrr7YzJuyTxuVBGdRAbm"),
+			wantIdentity: connector.Identity{
+				Email:         "jane@example.com",
+				Username:      "jane",
+				UserID:        "foobar",
+				EmailVerified: true,
+			},
+		},
+		{
+			name:     "valid password timeout cost",
+			email:    "jane@example.com",
+			password: pw,
+			// bcrypt hash of the value "test1" with cost 20
+			pwHash:    []byte("$2a$20$yODn5quqK9MZdePqYLs6Y.Jr4cOO1P0aXsKz0eTa2rxOmu8e7ETpi"),
+			wantedErr: fmt.Sprintf("password-hash comparison timeout: your bcrypt cost = 20, recommended cost = %d", recCost),
+		},
+		{
+			name:     "invalid password min cost",
+			email:    "jane@example.com",
+			password: pw,
+			// bcrypt hash of the value "test2" with cost 4
+			pwHash:      []byte("$2a$04$pX8wwwpxw8xlXrToYaEgZemK0JIibMZYXPsgau7aPDoGyHPF73br."),
+			wantInvalid: true,
+		},
+		{
+			name:     "invalid password timeout cost",
+			email:    "jane@example.com",
+			password: pw,
+			// bcrypt hash of the value "test2" with cost 20
+			pwHash:    []byte("$2a$20$WBD9cs63Zf0zqS99yyrQhODoDXphWw8MlYqVYRiftJH.lRJ1stnAa"),
+			wantedErr: fmt.Sprintf("password-hash comparison timeout: your bcrypt cost = 20, recommended cost = %d", recCost),
+		},
+	}
+
+	sEmail, sUsername, sUserID := "jane@example.com", "jane", "foobar"
+	for _, tc := range tests {
+		// Clean up before new test case
+		s.DeletePassword(sEmail)
+
+		s.CreatePassword(storage.Password{
+			Email:    sEmail,
+			Username: sUsername,
+			UserID:   sUserID,
+			Hash:     tc.pwHash,
+		})
+
+		ident, valid, err := conn.Login(context.Background(), connector.Scopes{}, tc.email, tc.password)
+		if err != nil {
+			if err.Error() != tc.wantedErr {
+				t.Errorf("%s: error was incorrect:\n%v", tc.name, err)
+			}
+			continue
+		}
+
+		if tc.wantedErr != "" {
+			t.Errorf("%s: expected error", tc.name)
+			continue
+		}
+
+		if !valid {
+			if !tc.wantInvalid {
+				t.Errorf("%s: expected valid response", tc.name)
+			}
+			continue
+		}
+
+		if tc.wantInvalid {
+			t.Errorf("%s: expected invalid response", tc.name)
+			continue
+		}
+
+		if diff := pretty.Compare(tc.wantIdentity, ident); diff != "" {
+			t.Errorf("%s: %s", tc.email, diff)
+		}
+	}
+
+}
+
 type storageWithKeysTrigger struct {
 	storage.Storage
 	f func()