prevent creating and dropping mysql and information_schema databases (#2775)

Author: jycor

enginetest/queries/information_schema_queries.go

@@ -1807,6 +1807,27 @@ from information_schema.routines where routine_schema = 'mydb' and routine_type
 			},
 		},
 	},
+	{
+		Name: "test information_schema database",
+		Assertions: []ScriptTestAssertion{
+			{
+				Query:    "show databases like 'information_schema';",
+				Expected: []sql.Row{{"information_schema"}},
+			},
+			{
+				Query:       "create database information_schema;",
+				ExpectedErr: sql.ErrDatabaseExists,
+			},
+			{
+				Query:          "drop database information_schema;",
+				ExpectedErrStr: "unable to drop database: information_schema",
+			},
+			{
+				Query:    "show databases like 'information_schema';",
+				Expected: []sql.Row{{"information_schema"}},
+			},
+		},
+	},
 }
 
 var SkippedInfoSchemaScripts = []ScriptTest{

enginetest/queries/mysql_db_queries.go

@@ -38,4 +38,25 @@ var MySqlDbTests = []ScriptTest{
 			},
 		},
 	},
+	{
+		Name: "test mysql database",
+		Assertions: []ScriptTestAssertion{
+			{
+				Query:    "show databases like 'mysql';",
+				Expected: []sql.Row{{"mysql"}},
+			},
+			{
+				Query:       "create database mysql;",
+				ExpectedErr: sql.ErrDatabaseExists,
+			},
+			{
+				Query:          "drop database mysql;",
+				ExpectedErrStr: "unable to drop database: mysql",
+			},
+			{
+				Query:    "show databases like 'mysql';",
+				Expected: []sql.Row{{"mysql"}},
+			},
+		},
+	},
 }

sql/analyzer/catalog.go

@@ -153,11 +153,13 @@ func (c *Catalog) RemoveDatabase(ctx *sql.Context, dbName string) error {
 	defer c.mu.Unlock()
 
 	mut, ok := c.DbProvider.(sql.MutableDatabaseProvider)
-	if ok {
-		return mut.DropDatabase(ctx, dbName)
-	} else {
+	if !ok {
 		return sql.ErrImmutableDatabaseProvider.New()
 	}
+	if strings.EqualFold(dbName, "information_schema") || (c.MySQLDb.Enabled() && strings.EqualFold(dbName, "mysql")) {
+		return fmt.Errorf("unable to drop database: %s", dbName)
+	}
+	return mut.DropDatabase(ctx, dbName)
 }
 
 func (c *Catalog) HasDatabase(ctx *sql.Context, db string) bool {

sql/mysql_db/privileged_database_provider.go

@@ -80,6 +80,10 @@ func (pdp PrivilegedDatabaseProvider) Database(ctx *sql.Context, name string) (s
 
 // HasDatabase implements the interface sql.DatabaseProvider.
 func (pdp PrivilegedDatabaseProvider) HasDatabase(ctx *sql.Context, name string) bool {
+	if strings.EqualFold(name, "mysql") {
+		return true
+	}
+
 	db, err := pdp.provider.Database(ctx, name)
 	if sql.ErrDatabaseNotFound.Is(err) {
 		// continue to check below, which will deny access or return not found as appropriate