cherry pick pingcap#33703 to release-5.2

Signed-off-by: ti-srebot <[email protected]>

server/conn.go

@@ -2184,8 +2184,13 @@ func (cc *clientConn) handleChangeUser(ctx context.Context, data []byte) error {
 	if err != nil {
 		logutil.Logger(ctx).Debug("close old context failed", zap.Error(err))
 	}
+<<<<<<< HEAD
 	err = cc.openSessionAndDoAuth(pass)
 	if err != nil {
+=======
+	cc.ctx = nil
+	if err := cc.openSessionAndDoAuth(pass, ""); err != nil {
+>>>>>>> 9fecc8a9b... server: set 'clientConn.ctx = nil' to clean the context when changeUser. (#33703)
 		return err
 	}
 	return cc.handleCommonConnectionReset(ctx)

server/conn_test.go

@@ -41,6 +41,7 @@ import (
 	"github.com/tikv/client-go/v2/testutils"
 )
 
+<<<<<<< HEAD
 type ConnTestSuite struct {
 	dom   *domain.Domain
 	store kv.Storage
@@ -75,6 +76,128 @@ func (ts *ConnTestSuite) TearDownSuite(c *C) {
 
 func (ts *ConnTestSuite) TestMalformHandshakeHeader(c *C) {
 	c.Parallel()
+=======
+type Issue33699CheckType struct {
+	name              string
+	defVal            string
+	setVal            string
+	isSessionVariable bool
+}
+
+func (c *Issue33699CheckType) toSetSessionVar() string {
+	if c.isSessionVariable {
+		return fmt.Sprintf("set session %s=%s", c.name, c.setVal)
+	}
+	return fmt.Sprintf("set @%s=%s", c.name, c.setVal)
+}
+
+func (c *Issue33699CheckType) toGetSessionVar() string {
+	if c.isSessionVariable {
+		return fmt.Sprintf("select @@session.%s", c.name)
+	}
+	return fmt.Sprintf("select @%s", c.name)
+}
+
+func TestIssue33699(t *testing.T) {
+	store, clean := testkit.CreateMockStore(t)
+	defer clean()
+
+	var outBuffer bytes.Buffer
+	tidbdrv := NewTiDBDriver(store)
+	cfg := newTestConfig()
+	cfg.Port, cfg.Status.StatusPort = 0, 0
+	cfg.Status.ReportStatus = false
+	server, err := NewServer(cfg, tidbdrv)
+	require.NoError(t, err)
+	defer server.Close()
+
+	cc := &clientConn{
+		connectionID: 1,
+		salt:         []byte{0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F, 0x10, 0x11, 0x12, 0x13, 0x14},
+		server:       server,
+		pkt: &packetIO{
+			bufWriter: bufio.NewWriter(&outBuffer),
+		},
+		collation:  mysql.DefaultCollationID,
+		peerHost:   "localhost",
+		alloc:      arena.NewAllocator(512),
+		chunkAlloc: chunk.NewAllocator(),
+		capability: mysql.ClientProtocol41,
+	}
+
+	tk := testkit.NewTestKit(t, store)
+	ctx := &TiDBContext{Session: tk.Session()}
+	cc.ctx = ctx
+
+	// change user.
+	doChangeUser := func() {
+		userData := append([]byte("root"), 0x0, 0x0)
+		userData = append(userData, []byte("test")...)
+		userData = append(userData, 0x0)
+		changeUserReq := dispatchInput{
+			com: mysql.ComChangeUser,
+			in:  userData,
+			err: nil,
+			out: []byte{0x7, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x2, 0x0, 0x0, 0x0},
+		}
+		inBytes := append([]byte{changeUserReq.com}, changeUserReq.in...)
+		err = cc.dispatch(context.Background(), inBytes)
+		require.Equal(t, changeUserReq.err, err)
+		if err == nil {
+			err = cc.flush(context.TODO())
+			require.NoError(t, err)
+			require.Equal(t, changeUserReq.out, outBuffer.Bytes())
+		} else {
+			_ = cc.flush(context.TODO())
+		}
+		outBuffer.Reset()
+	}
+	// check variable.
+	checks := []Issue33699CheckType{
+		{ // self define.
+			"a",
+			"<nil>",
+			"1",
+			false,
+		},
+		{ // session variable
+			"net_read_timeout",
+			"30",
+			"1234",
+			true,
+		},
+		{
+			"net_write_timeout",
+			"60",
+			"1234",
+			true,
+		},
+	}
+
+	// default;
+	for _, ck := range checks {
+		tk.MustQuery(ck.toGetSessionVar()).Check(testkit.Rows(ck.defVal))
+	}
+	// set;
+	for _, ck := range checks {
+		tk.MustExec(ck.toSetSessionVar())
+	}
+	// check after set.
+	for _, ck := range checks {
+		tk.MustQuery(ck.toGetSessionVar()).Check(testkit.Rows(ck.setVal))
+	}
+	doChangeUser()
+	require.NotEqual(t, ctx, cc.ctx)
+	require.NotEqual(t, ctx.Session, cc.ctx.Session)
+	// new session,so values is defaults;
+	tk.SetSession(cc.ctx.Session) // set new session.
+	for _, ck := range checks {
+		tk.MustQuery(ck.toGetSessionVar()).Check(testkit.Rows(ck.defVal))
+	}
+}
+
+func TestMalformHandshakeHeader(t *testing.T) {
+>>>>>>> 9fecc8a9b... server: set 'clientConn.ctx = nil' to clean the context when changeUser. (#33703)
 	data := []byte{0x00}
 	var p handshakeResponse41
 	_, err := parseHandshakeResponseHeader(context.Background(), &p, data)