Bug#16372: Server crashes when test 'conc_sys' is running

Concurrent read and update of privilege structures (like simultaneous
run of SHOW GRANTS and ADD USER) could result in server crash.

Ensure that proper locking of ACL structures is done.

No test case is provided because this bug can't be reproduced
deterministically.

sql/sql_acl.cc

@@ -894,6 +894,8 @@ static void acl_update_user(const char *user, const char *host,
 			    USER_RESOURCES  *mqh,
 			    ulong privileges)
 {
+  safe_mutex_assert_owner(&acl_cache->lock);
+
   for (uint i=0 ; i < acl_users.elements ; i++)
   {
     ACL_USER *acl_user=dynamic_element(&acl_users,i,ACL_USER*);
@@ -942,6 +944,9 @@ static void acl_insert_user(const char *user, const char *host,
 			    ulong privileges)
 {
   ACL_USER acl_user;
+
+  safe_mutex_assert_owner(&acl_cache->lock);
+
   acl_user.user=*user ? strdup_root(&mem,user) : 0;
   update_hostname(&acl_user.host, *host ? strdup_root(&mem, host): 0);
   acl_user.access=privileges;
@@ -973,6 +978,8 @@ static void acl_insert_user(const char *user, const char *host,
 static void acl_update_db(const char *user, const char *host, const char *db,
 			  ulong privileges)
 {
+  safe_mutex_assert_owner(&acl_cache->lock);
+
   for (uint i=0 ; i < acl_dbs.elements ; i++)
   {
     ACL_DB *acl_db=dynamic_element(&acl_dbs,i,ACL_DB*);
@@ -1358,6 +1365,9 @@ find_acl_user(const char *host, const char *user, my_bool exact)
 {
   DBUG_ENTER("find_acl_user");
   DBUG_PRINT("enter",("host: '%s'  user: '%s'",host,user));
+
+  safe_mutex_assert_owner(&acl_cache->lock);
+
   for (uint i=0 ; i < acl_users.elements ; i++)
   {
     ACL_USER *acl_user=dynamic_element(&acl_users,i,ACL_USER*);
@@ -1370,7 +1380,7 @@ find_acl_user(const char *host, const char *user, my_bool exact)
     if (!acl_user->user && !user[0] ||
 	acl_user->user && !strcmp(user,acl_user->user))
     {
-      if (exact ? !my_strcasecmp(&my_charset_latin1, host,
+      if (exact ? !my_strcasecmp(system_charset_info, host,
                                  acl_user->host.hostname ?
 				 acl_user->host.hostname : "") :
           compare_hostname(&acl_user->host,host,host))
@@ -2445,6 +2455,7 @@ int mysql_table_grant(THD *thd, TABLE_LIST *table_list,
     create_new_users= test_if_create_new_users(thd);
   int result=0;
   rw_wrlock(&LOCK_grant);
+  pthread_mutex_lock(&acl_cache->lock);
   MEM_ROOT *old_root= thd->mem_root;
   thd->mem_root= &memex;
 
@@ -2460,10 +2471,8 @@ int mysql_table_grant(THD *thd, TABLE_LIST *table_list,
       continue;
     }
     /* Create user if needed */
-    pthread_mutex_lock(&acl_cache->lock);
     error=replace_user_table(thd, tables[0].table, *Str,
 			     0, revoke_grant, create_new_users);
-    pthread_mutex_unlock(&acl_cache->lock);
     if (error)
     {
       result= -1;				// Remember error
@@ -2552,6 +2561,7 @@ int mysql_table_grant(THD *thd, TABLE_LIST *table_list,
   }
   grant_option=TRUE;
   thd->mem_root= old_root;
+  pthread_mutex_unlock(&acl_cache->lock);
   rw_unlock(&LOCK_grant);
   if (!result)
     send_ok(thd);
@@ -3203,6 +3213,9 @@ int mysql_show_grants(THD *thd,LEX_USER *lex_user)
     DBUG_RETURN(-1);
   }
 
+  rw_rdlock(&LOCK_grant);
+  VOID(pthread_mutex_lock(&acl_cache->lock));
+
   for (counter=0 ; counter < acl_users.elements ; counter++)
   {
     const char *user,*host;
@@ -3217,6 +3230,9 @@ int mysql_show_grants(THD *thd,LEX_USER *lex_user)
   }
   if (counter == acl_users.elements)
   {
+    VOID(pthread_mutex_unlock(&acl_cache->lock));
+    rw_unlock(&LOCK_grant);
+
     my_error(ER_NONEXISTING_GRANT, MYF(0),
              lex_user->user.str, lex_user->host.str);
     DBUG_RETURN(-1);
@@ -3230,10 +3246,12 @@ int mysql_show_grants(THD *thd,LEX_USER *lex_user)
 	  lex_user->host.str,NullS);
   field_list.push_back(field);
   if (protocol->send_fields(&field_list,1))
-    DBUG_RETURN(-1);
+  {
+    VOID(pthread_mutex_unlock(&acl_cache->lock));
+    rw_unlock(&LOCK_grant);
 
-  rw_wrlock(&LOCK_grant);
-  VOID(pthread_mutex_lock(&acl_cache->lock));
+    DBUG_RETURN(-1);
+  }
 
   /* Add first global access grants */
   {
@@ -3540,10 +3558,15 @@ void get_privilege_desc(char *to, uint max_length, ulong access)
 void get_mqh(const char *user, const char *host, USER_CONN *uc)
 {
   ACL_USER *acl_user;
+
+  pthread_mutex_lock(&acl_cache->lock);
+
   if (initialized && (acl_user= find_acl_user(host,user, FALSE)))
     uc->user_resources= acl_user->user_resource;
   else
     bzero((char*) &uc->user_resources, sizeof(uc->user_resources));
+
+  pthread_mutex_unlock(&acl_cache->lock);
 }
 
 int open_grant_tables(THD *thd, TABLE_LIST *tables)
@@ -3602,6 +3625,8 @@ ACL_USER *check_acl_user(LEX_USER *user_name,
   ACL_USER *acl_user= 0;
   uint counter;
 
+  safe_mutex_assert_owner(&acl_cache->lock);
+
   for (counter= 0 ; counter < acl_users.elements ; counter++)
   {
     const char *user,*host;