From 608eb95284540e1e1ad8b969b6d767a7592647d4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Markus=20M=C3=A4kel=C3=A4?= <markus.makela@mariadb.com>
Date: Thu, 2 Jul 2020 08:11:16 +0300
Subject: [PATCH] MXS-3055: Prevent sending of an extra COM_QUIT

If the protocol routes a COM_QUIT packet to the backend, it must not
generate a packet when it is shutting down. This could cause unexpected
write errors if the backend server managed to close the socket before the
write was done.
---
 include/maxscale/protocol/mysql.hh                  |  1 +
 .../protocol/MySQL/mariadbbackend/mysql_backend.cc  | 13 +++++++++++--
 server/modules/protocol/MySQL/mysql_common.cc       |  1 +
 3 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/include/maxscale/protocol/mysql.hh b/include/maxscale/protocol/mysql.hh
index 5dc4ee79b..4ae7f3a9a 100644
--- a/include/maxscale/protocol/mysql.hh
+++ b/include/maxscale/protocol/mysql.hh
@@ -340,6 +340,7 @@ typedef struct
     bool                   collect_result;              /*< Collect the next result set as one buffer */
     bool                   changing_user;
     bool                   track_state;     /*< Track session state */
+    bool                   send_com_quit;
     uint32_t               num_eof_packets; /*< Encountered eof packet number, used for check
                                              * packet type */
     bool large_query;                       /*< Whether to ignore the command byte of the next
diff --git a/server/modules/protocol/MySQL/mariadbbackend/mysql_backend.cc b/server/modules/protocol/MySQL/mariadbbackend/mysql_backend.cc
index af303d157..d50b25fe3 100644
--- a/server/modules/protocol/MySQL/mariadbbackend/mysql_backend.cc
+++ b/server/modules/protocol/MySQL/mariadbbackend/mysql_backend.cc
@@ -1286,6 +1286,12 @@ static int gw_MySQLWrite_backend(DCB* dcb, GWBUF* queue)
             }
             else
             {
+
+                if (cmd == MXS_COM_QUIT)
+                {
+                    backend_protocol->send_com_quit = false;
+                }
+
                 if (GWBUF_IS_IGNORABLE(queue))
                 {
                     /** The response to this command should be ignored */
@@ -1398,8 +1404,11 @@ static int gw_backend_close(DCB* dcb)
     mxb_assert(dcb->session || dcb->persistentstart);
     MySQLProtocol* proto = (MySQLProtocol*)dcb->protocol;
 
-    /** Send COM_QUIT to the backend being closed */
-    dcb_write(dcb, mysql_create_com_quit(NULL, 0));
+    if (proto->send_com_quit && proto->protocol_auth_state == MXS_AUTH_STATE_COMPLETE)
+    {
+        // Send a COM_QUIT to the backend being closed, we haven't routed one to it yet.
+        dcb_write(dcb, mysql_create_com_quit(NULL, 0));
+    }
 
     /** Free protocol data */
     mysql_protocol_done(dcb);
diff --git a/server/modules/protocol/MySQL/mysql_common.cc b/server/modules/protocol/MySQL/mysql_common.cc
index 6cb64747c..af501f8f4 100644
--- a/server/modules/protocol/MySQL/mysql_common.cc
+++ b/server/modules/protocol/MySQL/mysql_common.cc
@@ -64,6 +64,7 @@ MySQLProtocol* mysql_protocol_init(DCB* dcb, int fd)
     p->num_eof_packets = 0;
     p->large_query = false;
     p->track_state = false;
+    p->send_com_quit = true;
     /*< Assign fd with protocol */
     p->fd = fd;
     p->owner_dcb = dcb;