executor: let flush privileges do nothing when skip-grant-table is configured

executor/executor_test.go

@@ -96,6 +96,7 @@ var _ = Suite(&testUpdateSuite{})
 var _ = Suite(&testOOMSuite{})
 var _ = Suite(&testPointGetSuite{})
 var _ = Suite(&testRecoverTable{})
+var _ = Suite(&testFlushSuite{})
 
 type testSuite struct {
 	cluster   *mocktikv.Cluster

executor/simple.go

@@ -812,6 +812,13 @@ func (e *SimpleExec) executeFlush(s *ast.FlushStmt) error {
 			return errors.New("FLUSH TABLES WITH READ LOCK is not supported.  Please use @@tidb_snapshot")
 		}
 	case ast.FlushPrivileges:
+		// If skip-grant-table is configured, do not flush privileges.
+		// Because LoadPrivilegeLoop does not run and the privilege Handle is nil,
+		// Call dom.PrivilegeHandle().Update would panic.
+		if config.GetGlobalConfig().Security.SkipGrantTable {
+			return nil
+		}
+
 		dom := domain.GetDomain(e.ctx)
 		sysSessionPool := dom.SysSessionPool()
 		ctx, err := sysSessionPool.Get()

executor/simple_test.go

@@ -16,17 +16,19 @@ package executor_test
 import (
 	"context"
 
-	"github.com/pingcap/tidb/planner/core"
-
 	. "github.com/pingcap/check"
 	"github.com/pingcap/parser/auth"
 	"github.com/pingcap/parser/model"
 	"github.com/pingcap/parser/mysql"
 	"github.com/pingcap/parser/terror"
+	"github.com/pingcap/tidb/config"
 	"github.com/pingcap/tidb/domain"
 	"github.com/pingcap/tidb/executor"
+	"github.com/pingcap/tidb/planner/core"
 	"github.com/pingcap/tidb/session"
 	"github.com/pingcap/tidb/sessionctx"
+	"github.com/pingcap/tidb/store/mockstore"
+	"github.com/pingcap/tidb/store/mockstore/mocktikv"
 	"github.com/pingcap/tidb/util/testkit"
 	"github.com/pingcap/tidb/util/testutil"
 )
@@ -394,6 +396,31 @@ func (s *testSuite3) TestFlushPrivileges(c *C) {
 	// After flush.
 	_, err = se.Execute(ctx, `SELECT Password FROM mysql.User WHERE User="testflush" and Host="localhost"`)
 	c.Check(err, IsNil)
+
+}
+
+type testFlushSuite struct{}
+
+func (s *testFlushSuite) TestFlushPrivilegesPanic(c *C) {
+	// Run in a separate suite because this test need to set SkipGrantTable config.
+	cluster := mocktikv.NewCluster()
+	mocktikv.BootstrapWithSingleStore(cluster)
+	mvccStore := mocktikv.MustNewMVCCStore()
+	store, err := mockstore.NewMockTikvStore(
+		mockstore.WithCluster(cluster),
+		mockstore.WithMVCCStore(mvccStore),
+	)
+	c.Assert(err, IsNil)
+	defer store.Close()
+
+	config.GetGlobalConfig().Security.SkipGrantTable = true
+	dom, err := session.BootstrapSession(store)
+	c.Assert(err, IsNil)
+	defer dom.Close()
+
+	tk := testkit.NewTestKit(c, store)
+	tk.MustExec("FLUSH PRIVILEGES")
+	config.GetGlobalConfig().Security.SkipGrantTable = false
 }
 
 func (s *testSuite3) TestDropStats(c *C) {