From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1753929Ab3FTHBH (ORCPT <rfc822;w@1wt.eu>);
	Thu, 20 Jun 2013 03:01:07 -0400
Received: from mail-pd0-f182.google.com ([209.85.192.182]:36492 "EHLO
	mail-pd0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751921Ab3FTHBG (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Thu, 20 Jun 2013 03:01:06 -0400
Message-ID: <51C2A8AA.5010902@gmail.com>
Date: Thu, 20 Jun 2013 15:00:58 +0800
From: xiaoming gao <gxm.linux.kernel@gmail.com>
User-Agent: Mozilla/5.0 (Windows NT 5.1; rv:17.0) Gecko/20130509 Thunderbird/17.0.6
MIME-Version: 1.0
To: Eric Dumazet <eric.dumazet@gmail.com>
CC: stephen@networkplumber.org, davem@davemloft.net,
        bridge@lists.linux-foundation.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] net bridge: add null pointer check, fix panic
References: <51C2710D.2060405@gmail.com> <51C2721B.9050603@gmail.com> <1371704129.3252.356.camel@edumazet-glaptop>
In-Reply-To: <1371704129.3252.356.camel@edumazet-glaptop>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

Eric Dumazet said, at 2013-6-20 12:55:
> On Thu, 2013-06-20 at 11:08 +0800, xiaoming gao wrote:
>> From: newtongao <newtongao@tencent.com>
>> Date: Wed, 19 Jun 2013 14:58:33 +0800
>> Subject: [PATCH] net bridge: add null pointer check,fix panic
>>
>> in kernel 3.0, br_port_get_rcu() may return NULL when network interface be deleting from bridge,
>> but in function br_handle_frame and br_handle_local_finish, the pointer didn't be checked before using,
>> so all br_port_get_rcu callers must do null check,or there occurs the null pointer panic.
>>
>> kernel 3.4 also has this bug,i have verified.
>> mainline kernel still did not  check br_port_get_rcu()'s NULL pointer, but i have not tested it yet.
> 
> Please check current version before sending a patch.
> 
> This was most probably fixed in commit 00cfec37484761a44
> ("net: add a synchronize_net() in netdev_rx_handler_unregister()")
> 
> Thanks
> 
> 
HI Eric
the problem is as follow:
br_del_if()-->del_nbp():

list_del_rcu(&p->list);
dev->priv_flags &= ~IFF_BRIDGE_PORT;

------>at this point, the nic be deleting still have rx_handler , so , may in br_handle_frame()
------>br_port_exists() will return false,so br_get_port_rcu() will return NULL
------>so in br_handle_frame , there will be a null panic.

netdev_rx_handler_unregister(dev);
synchronize_net();


i have checked commit 00cfec37484761a44, i think it didn't fix this bug..

thanks.