From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752221Ab2DQKWN (ORCPT ); Tue, 17 Apr 2012 06:22:13 -0400 Received: from mx1.redhat.com ([209.132.183.28]:16743 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751334Ab2DQKWL (ORCPT ); Tue, 17 Apr 2012 06:22:11 -0400 Date: Tue, 17 Apr 2012 13:22:20 +0300 From: "Michael S. Tsirkin" To: Jason Wang Cc: netdev@vger.kernel.org, xma@us.ibm.com, davem@davemloft.net, linux-kernel@vger.kernel.org, ebiederm@xmission.com Subject: Re: [PATCH 5/6] vhost_net: fix use after free of vq->ubufs Message-ID: <20120417102220.GC20905@redhat.com> References: <20120416060749.14140.19433.stgit@intel-e5620-16-2.englab.nay.redhat.com> <20120416060825.14140.32069.stgit@intel-e5620-16-2.englab.nay.redhat.com> <20120416132841.GB13113@redhat.com> <4F8CE14E.5080508@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4F8CE14E.5080508@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 17, 2012 at 11:19:42AM +0800, Jason Wang wrote: > On 04/16/2012 09:28 PM, Michael S. Tsirkin wrote: > >On Mon, Apr 16, 2012 at 02:08:25PM +0800, Jason Wang wrote: > >>When zerocopy socket is used, ubufs pointer were used in handle_tx() > >>without any validation. This would cause NULL pointer deference after > >>it has been freed in vhost_net_set_backend(). Fix this by check the > >>pointer before using it. > >> > >>Signed-off-by: Jason Wang > > > >OK so it's NULL dereference and not user after free :) > >Also could you clarify how does this happen pls? > >Don't we always initialize ubufs when vhost_sock_zcopy is set? > > The problem happens when we want to disable backend. At this time > ubufs were assigned to NULL and it may be dereferenced by > handle_tx(): Heh, I see. How about - zcopy = vhost_sock_zcopy(sock); + zcopy = vq->ubufs; -- MST