MDEV-4422 SHOW PROCESSLIST reference to THD::db not protected against simultaneous updates

protect THD::db with THD::LOCK_thd_data

1 files changed, 10 insertions, 2 deletions

diff --git a/sql/sql_class.h b/sql/sql_class.h
index 52acba682a2..b11e18777d5 100644
--- a/sql/sql_class.h
+++ b/sql/sql_class.h
@@ -1605,6 +1605,7 @@ public:
     Protects THD data accessed from other threads:
     - thd->query and thd->query_length (used by SHOW ENGINE
       INNODB STATUS and SHOW PROCESSLIST
+    - thd->db and thd->db_length (used in SHOW PROCESSLIST)
     - thd->mysys_var (used by KILL statement and shutdown).
     Is locked when THD is deleted.
   */
@@ -2838,6 +2839,7 @@ public:
   */
   bool set_db(const char *new_db, size_t new_db_len)
   {
+    mysql_mutex_lock(&LOCK_thd_data);
     /* Do not reallocate memory if current chunk is big enough. */
     if (db && new_db && db_length >= new_db_len)
       memcpy(db, new_db, new_db_len+1);
@@ -2850,6 +2852,7 @@ public:
         db= NULL;
     }
     db_length= db ? new_db_len : 0;
+    mysql_mutex_unlock(&LOCK_thd_data);
     return new_db && !db;
   }
 
@@ -2866,8 +2869,13 @@ public:
   */
   void reset_db(char *new_db, size_t new_db_len)
   {
-    db= new_db;
-    db_length= new_db_len;
+    if (new_db != db || new_db_len != db_length)
+    {
+      mysql_mutex_lock(&LOCK_thd_data);
+      db= new_db;
+      db_length= new_db_len;
+      mysql_mutex_unlock(&LOCK_thd_data);
+    }
   }
   /*
     Copy the current database to the argument. Use the current arena to