Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751612AbaKFH6r (ORCPT ); Thu, 6 Nov 2014 02:58:47 -0500 Received: from antispam.ahnlab.com ([210.121.169.55]:59179 "EHLO antispam.ahnlab.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751070AbaKFH6p (ORCPT ); Thu, 6 Nov 2014 02:58:45 -0500 X-Original-SENDERIP: 172.16.11.209 X-Original-MAILFROM: suhyun.park@ahnlab.com From: =?ks_c_5601-1987?B?udq89sf2?= To: Toshiaki Makita , Stephen Hemminger , "David S. Miller" CC: "bridge@lists.linux-foundation.org" , "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: RE: [PATCH] bridge: missing null bridge device check causing null pointer dereference (bugfix) Thread-Topic: [PATCH] bridge: missing null bridge device check causing null pointer dereference (bugfix) Thread-Index: AQHP+YqrhNePGBbJkEOg7Nz1l90pj5xSlqaAgACjdfA= Date: Thu, 6 Nov 2014 07:58:41 +0000 Message-ID: <8D1F1238A24CE743B8F3CED0F137C69E408AA087@EXMB02.ahnbang.ahnlab.com> References: <1415255192-13584-1-git-send-email-suhyun.park@ahnlab.com> <545B1E27.3080302@lab.ntt.co.jp> In-Reply-To: <545B1E27.3080302@lab.ntt.co.jp> Accept-Language: ko-KR, en-US Content-Language: ko-KR X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [172.20.32.26] Content-Type: text/plain; charset="ks_c_5601-1987" MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from base64 to 8bit by nfs id sA67wqet000986 >-----Original Message----- >From: Toshiaki Makita [mailto:makita.toshiaki@lab.ntt.co.jp] >Sent: Thursday, November 06, 2014 4:07 PM >To: ?ڼ???; Stephen Hemminger; David S. Miller >Cc: bridge@lists.linux-foundation.org; netdev@vger.kernel.org; linux- >kernel@vger.kernel.org >Subject: Re: [PATCH] bridge: missing null bridge device check causing null >pointer dereference (bugfix) > >On 2014/11/06 15:26, Su-Hyun Park wrote: >> the bridge device can be null if the bridge is being deleted while >> processing the packet, which causes the null pointer dereference in >switch statement. > >How can this happen?? >It is guarded by rcu. >netdev_rx_handler_unregister() ensures rx_handler_data is non NULL. > The RCU protect rx_handler_data, not the bridge member port. It can be NULL according to below code. static inline struct net_bridge_port *br_port_get_rcu(const struct net_device *dev) { struct net_bridge_port *port = rcu_dereference(dev->rx_handler_data); return br_port_exists(dev) ? port : NULL; } The crash happens at the below switch statement in br_handle_frame, where p is NULL. switch (p->state) >> >> crash dump snippet: >> >> <1>BUG: unable to handle kernel NULL pointer dereference at >> 0000000000000021 >> <1>IP: [] br_handle_frame+0xe6/0x270 >> >> <0>Code: 4c 0f 44 f0 89 f8 66 33 15 32 52 24 00 66 33 05 29 52 24 00 >> 09 c2 89 >> f0 66 33 05 22 52 24 00 80 e4 f0 66 09 c2 0f 84 eb 00 00 00 <41> 0f b6 >> 46 21 3c 02 74 61 3c 03 74 1d 48 89 df e8 d5 bc f0 ff >> --- >> net/bridge/br_input.c | 2 ++ >> 1 file changed, 2 insertions(+) >> >> diff --git a/net/bridge/br_input.c b/net/bridge/br_input.c index >> 6fd5522..7e899ca 100644 >> --- a/net/bridge/br_input.c >> +++ b/net/bridge/br_input.c >> @@ -176,6 +176,8 @@ rx_handler_result_t br_handle_frame(struct sk_buff >**pskb) >> return RX_HANDLER_CONSUMED; >> >> p = br_port_get_rcu(skb->dev); >> + if (!p) >> + goto drop; >> >> if (unlikely(is_link_local_ether_addr(dest))) { >> u16 fwd_mask = p->br->group_fwd_mask_required; >> > ????{.n?+???????+%?????ݶ??w??{.n?+????{??G?????{ay?ʇڙ?,j??f???h?????????z_??(?階?ݢj"???m??????G????????????&???~???iO???z??v?^?m????????????I?