BUG#15775 "drop user" command does not refresh acl_check_hosts

   - DROP USER command didn't reload the acl_check_hosts cache causing subsequent 
     connect's via TCP to fail randomly.
   - 4.1 version

mysql-test/r/grant2.result

@@ -131,3 +131,15 @@ lock table mysql.user write;
  revoke all on *.* from 'mysqltest_1'@'localhost';
 unlock tables;
 drop user 'mysqltest_1'@'localhost';
+insert into mysql.user (user, host) values
+('mysqltest_1', 'host1'),
+('mysqltest_2', 'host2'),
+('mysqltest_3', 'host3'),
+('mysqltest_4', 'host4'),
+('mysqltest_5', 'host5'),
+('mysqltest_6', 'host6'),
+('mysqltest_7', 'host7');
+flush privileges;
+drop user mysqltest_3@host3;
+drop user mysqltest_1@host1, mysqltest_2@host2, mysqltest_4@host4,
+mysqltest_5@host5, mysqltest_6@host6, mysqltest_7@host7;

mysql-test/t/grant2.test

@@ -206,4 +206,37 @@ drop user 'mysqltest_1'@'localhost';
 disconnect con2root;
 disconnect con3root;
 
+#
+# Bug #15775: "drop user" command does not refresh acl_check_hosts
+#
+
+# Create some test users
+insert into mysql.user (user, host) values
+	('mysqltest_1', 'host1'),
+	('mysqltest_2', 'host2'),
+	('mysqltest_3', 'host3'),
+	('mysqltest_4', 'host4'),
+	('mysqltest_5', 'host5'),
+	('mysqltest_6', 'host6'),
+	('mysqltest_7', 'host7');
+flush privileges;
+
+# Drop one user
+drop user mysqltest_3@host3;
+
+# This connect failed before fix since the acl_check_hosts list was corrupted by the "drop user"
+connect (con8,127.0.0.1,root,,test,$MASTER_MYPORT,);
+disconnect con8;
+connection default;
+
+# Clean up - Drop all of the remaining users at once
+drop user mysqltest_1@host1, mysqltest_2@host2, mysqltest_4@host4,
+  mysqltest_5@host5, mysqltest_6@host6, mysqltest_7@host7;
+
+# Check that it's still possible to connect
+connect (con9,127.0.0.1,root,,test,$MASTER_MYPORT,);
+disconnect con9;
+connection default;
+
+
 # End of 4.1 tests

sql/sql_acl.cc

@@ -1151,7 +1151,7 @@ static void init_check_host(void)
 	if (j == acl_wild_hosts.elements)	// If new
 	  (void) push_dynamic(&acl_wild_hosts,(char*) &acl_user->host);
       }
-      else if (!hash_search(&acl_check_hosts,(byte*) &acl_user->host,
+      else if (!hash_search(&acl_check_hosts,(byte*) acl_user->host.hostname,
 			    (uint) strlen(acl_user->host.hostname)))
       {
 	if (my_hash_insert(&acl_check_hosts,(byte*) acl_user))
@@ -3719,17 +3719,25 @@ int mysql_drop_user(THD *thd, List <LEX_USER> &list)
 						     record[0])))
       {
 	tables[0].table->file->print_error(error, MYF(0));
-	DBUG_RETURN(-1);
+	result= -1;
+	goto end;
       }
       delete_dynamic_element(&acl_users, acl_userd);
     }
   }
 
+  if (result)
+    my_error(ER_DROP_USER, MYF(0));
+
+end:
+  /* Reload acl_check_hosts as its memory is mapped to acl_user */
+  delete_dynamic(&acl_wild_hosts);
+  hash_free(&acl_check_hosts);
+  init_check_host();
+
   VOID(pthread_mutex_unlock(&acl_cache->lock));
   rw_unlock(&LOCK_grant);
   close_thread_tables(thd);
-  if (result)
-    my_error(ER_DROP_USER, MYF(0));
   DBUG_RETURN(result);
 }