Bug#11765252 - READ OF FREED MEMORY WHEN "USE DB" AND

               "SHOW PROCESSLIST"

Analysis:
----------
The problem here is, if one connection changes its
default db and at the same time another connection executes
"SHOW PROCESSLIST", when it wants to read db of the another
connection then there is a chance of accessing the invalid
memory. 

The db name stored in THD is not guarded while changing user
DB and while reading the user DB in "SHOW PROCESSLIST".
So, if THD.db is freed by thd "owner" thread and if another
thread executing "SHOW PROCESSLIST" statement tries to read
and copy THD.db at the same time then we may endup in the issue
reported here.

Fix:
----------
Used mutex "LOCK_thd_data" to guard THD.db while freeing it
and while copying it to processlist.

mysql-test/include/have_valgrind.inc

+# include/have_valgrind.inc
+#
+# If some test should be run with only valgrind then skip it while running test
+# without it.
+#
+
+if (!$VALGRIND_TEST) {
+  --skip Need "--valgrind" 
+}
+
+

sql/sql_class.h

 /*
-   Copyright (c) 2000, 2012, Oracle and/or its affiliates. All rights reserved.
+   Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -2284,6 +2284,12 @@ public:
   */
   bool set_db(const char *new_db, size_t new_db_len)
   {
+    /*
+      Acquiring mutex LOCK_thd_data as we either free the memory allocated
+      for the database and reallocate the memory for the new db or memcpy
+      the new_db to the db.
+    */
+    pthread_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);
@@ -2293,6 +2299,7 @@ public:
       db= new_db ? my_strndup(new_db, new_db_len, MYF(MY_WME)) : NULL;
     }
     db_length= db ? new_db_len : 0;
+    pthread_mutex_unlock(&LOCK_thd_data);
     return new_db && !db;
   }
 

sql/sql_db.cc

 /*
-   Copyright (c) 2000, 2012, Oracle and/or its affiliates. All rights reserved.
+   Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -1469,10 +1469,12 @@ static void mysql_change_db_impl(THD *thd,
       we just call THD::reset_db(). Since THD::reset_db() does not releases
       the previous database name, we should do it explicitly.
     */
-
-    x_free(thd->db);
-
+    pthread_mutex_lock(&thd->LOCK_thd_data);
+    if (thd->db)
+      x_free(thd->db);
+    DEBUG_SYNC(thd, "after_freeing_thd_db");
     thd->reset_db(new_db_name->str, new_db_name->length);
+    pthread_mutex_unlock(&thd->LOCK_thd_data);
   }
 
   /* 2. Update security context. */

sql/sql_parse.cc

@@ -1231,7 +1231,9 @@ bool dispatch_command(enum enum_server_command command, THD *thd,
       if (save_user_connect)
 	decrease_user_connections(save_user_connect);
 #endif /* NO_EMBEDDED_ACCESS_CHECKS */
+      pthread_mutex_lock(&thd->LOCK_thd_data);
       x_free(save_db);
+      pthread_mutex_unlock(&thd->LOCK_thd_data);
       x_free(save_security_ctx.user);
     }
     break;

sql/sql_show.cc

-/* Copyright (c) 2000, 2012, Oracle and/or its affiliates. All rights reserved.
+/* Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -1847,8 +1847,6 @@ void mysqld_list_processes(THD *thd,const char *user, bool verbose)
 	  thd_info->host= thd->strdup(tmp_sctx->host_or_ip[0] ? 
                                       tmp_sctx->host_or_ip : 
                                       tmp_sctx->host ? tmp_sctx->host : "");
-        if ((thd_info->db=tmp->db))             // Safe test
-          thd_info->db=thd->strdup(thd_info->db);
         thd_info->command=(int) tmp->command;
         if ((mysys_var= tmp->mysys_var))
           pthread_mutex_lock(&mysys_var->mutex);
@@ -1871,6 +1869,7 @@ void mysqld_list_processes(THD *thd,const char *user, bool verbose)
           pthread_mutex_unlock(&mysys_var->mutex);
 
         thd_info->start_time= tmp->start_time;
+
         thd_info->query=0;
         /* Lock THD mutex that protects its data when looking at it. */
         pthread_mutex_lock(&tmp->LOCK_thd_data);
@@ -1879,7 +1878,11 @@ void mysqld_list_processes(THD *thd,const char *user, bool verbose)
           uint length= min(max_query_length, tmp->query_length());
           thd_info->query= (char*) thd->strmake(tmp->query(),length);
         }
+
+        if ((thd_info->db= tmp->db))             // Safe test
+          thd_info->db= thd->strdup(thd_info->db);
         pthread_mutex_unlock(&tmp->LOCK_thd_data);
+
         thread_infos.append(thd_info);
       }
     }
@@ -1934,7 +1937,7 @@ int fill_schema_processlist(THD* thd, TABLE_LIST* tables, COND* cond)
     {
       Security_context *tmp_sctx= tmp->security_ctx;
       struct st_my_thread_var *mysys_var;
-      const char *val;
+      const char *val, *db;
 
       if ((!tmp->vio_ok() && !tmp->system_thread) ||
           (user && (!tmp_sctx->user || strcmp(tmp_sctx->user, user))))
@@ -1959,13 +1962,6 @@ int fill_schema_processlist(THD* thd, TABLE_LIST* tables, COND* cond)
       else
         table->field[2]->store(tmp_sctx->host_or_ip,
                                strlen(tmp_sctx->host_or_ip), cs);
-      /* DB */
-      if (tmp->db)
-      {
-        table->field[3]->store(tmp->db, strlen(tmp->db), cs);
-        table->field[3]->set_notnull();
-      }
-
       if ((mysys_var= tmp->mysys_var))
         pthread_mutex_lock(&mysys_var->mutex);
       /* COMMAND */
@@ -2011,6 +2007,13 @@ int fill_schema_processlist(THD* thd, TABLE_LIST* tables, COND* cond)
                                    tmp->query_length()), cs);
         table->field[7]->set_notnull();
       }
+
+      /* DB */
+      if ((db= tmp->db))
+      {
+        table->field[3]->store(db, strlen(db), cs);
+        table->field[3]->set_notnull();
+      }
       pthread_mutex_unlock(&tmp->LOCK_thd_data);
 
       if (schema_table_store_record(thd, table))