server: set connection to TCP socket when unix and TCP used (#23463)

server/server.go

@@ -172,8 +172,11 @@ func (s *Server) newConn(conn net.Conn) *clientConn {
 	return cc
 }
 
+// isUnixSocket should ideally be a function of clientConnection!
+// But currently since unix-socket connections are forwarded to TCP when the server listens on both, it can really only be accurate on a server-level.
+// If the server is listening on both, it *must* return FALSE for remote-host authentication to be performed correctly. See #23460.
 func (s *Server) isUnixSocket() bool {
-	return s.cfg.Socket != ""
+	return s.cfg.Socket != "" && s.cfg.Port == 0
 }
 
 func (s *Server) forwardUnixSocketToTCP() {

server/tidb_test.go

@@ -248,6 +248,7 @@ func (ts *tidbTestSuite) TestStatusAPIWithTLS(c *C) {
 	cli.statusPort = getPortFromTCPAddr(server.statusListener.Addr())
 	go server.Run()
 	time.Sleep(time.Millisecond * 100)
+	c.Assert(server.isUnixSocket(), IsFalse) // If listening on tcp-only, return FALSE
 
 	// https connection should work.
 	ts.runTestStatusAPI(c)
@@ -348,6 +349,7 @@ func (ts *tidbTestSuite) TestSocketForwarding(c *C) {
 	cli.port = getPortFromTCPAddr(server.listener.Addr())
 	go server.Run()
 	time.Sleep(time.Millisecond * 100)
+	c.Assert(server.isUnixSocket(), IsFalse) // If listening on both, return FALSE
 	defer server.Close()
 
 	cli.runTestRegression(c, func(config *mysql.Config) {
@@ -371,6 +373,7 @@ func (ts *tidbTestSuite) TestSocket(c *C) {
 	c.Assert(err, IsNil)
 	go server.Run()
 	time.Sleep(time.Millisecond * 100)
+	c.Assert(server.isUnixSocket(), IsTrue) // If listening on socket-only, return TRUE
 	defer server.Close()
 
 	//a fake server client, config is override, just used to run tests