db: check errors in openDB

On the SQLite path openDB called db.DB() and configured the pool
before looking at the error from gorm.Open, and both backends
discarded the error from db.DB(). A failed open returned a
half-initialised *gorm.DB alongside the error, and a nil *sql.DB
from db.DB() would have been dereferenced.

Return early on either error so callers get a nil handle and the
original error.

hscontrol/db/db.go

@@ -446,16 +446,23 @@ func openDB(cfg types.DatabaseConfig) (*gorm.DB, error) {
 				Logger:      dbLogger,
 			},
 		)
+		if err != nil {
+			return nil, err
+		}
 
 		// The pure Go SQLite library does not handle locking in
 		// the same way as the C based one and we can't use the gorm
 		// connection pool as of 2022/02/23.
-		sqlDB, _ := db.DB()
+		sqlDB, err := db.DB()
+		if err != nil {
+			return nil, err
+		}
+
 		sqlDB.SetMaxIdleConns(1)
 		sqlDB.SetMaxOpenConns(1)
 		sqlDB.SetConnMaxIdleTime(time.Hour)
 
-		return db, err
+		return db, nil
 
 	case types.DatabasePostgres:
 		dbString := fmt.Sprintf(
@@ -493,7 +500,11 @@ func openDB(cfg types.DatabaseConfig) (*gorm.DB, error) {
 			return nil, err
 		}
 
-		sqlDB, _ := db.DB()
+		sqlDB, err := db.DB()
+		if err != nil {
+			return nil, err
+		}
+
 		sqlDB.SetMaxIdleConns(cfg.Postgres.MaxIdleConnections)
 		sqlDB.SetMaxOpenConns(cfg.Postgres.MaxOpenConnections)
 		sqlDB.SetConnMaxIdleTime(

hscontrol/db/db_test.go

@@ -910,3 +910,54 @@ func TestInterruptedInitSchemaRecovers(t *testing.T) {
 		require.NoError(t, err)
 	})
 }
+
+func TestOpenDBReturnsOpenError(t *testing.T) {
+	tests := []struct {
+		name string
+		cfg  func(t *testing.T) types.DatabaseConfig
+	}{
+		{
+			name: "sqlite-path-is-a-directory",
+			cfg: func(t *testing.T) types.DatabaseConfig {
+				t.Helper()
+
+				return types.DatabaseConfig{
+					Type:   types.DatabaseSqlite,
+					Sqlite: types.SqliteConfig{Path: t.TempDir()},
+				}
+			},
+		},
+		{
+			name: "postgres-unreachable-host",
+			cfg: func(t *testing.T) types.DatabaseConfig {
+				t.Helper()
+
+				return types.DatabaseConfig{
+					Type: types.DatabasePostgres,
+					Postgres: types.PostgresConfig{
+						Host: "127.0.0.1",
+						Port: 1,
+						Name: "headscale",
+						User: "headscale",
+						Ssl:  "false",
+					},
+				}
+			},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var (
+				db  *gorm.DB
+				err error
+			)
+
+			require.NotPanics(t, func() {
+				db, err = openDB(tt.cfg(t))
+			})
+			require.Error(t, err)
+			assert.Nil(t, db)
+		})
+	}
+}