From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Wang Subject: Re: [PATCH 5/6] vhost_net: fix use after free of vq->ubufs Date: Tue, 17 Apr 2012 18:47:04 +0800 Message-ID: <4F8D4A28.7030802@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> <20120417102220.GC20905@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, xma@us.ibm.com, davem@davemloft.net, linux-kernel@vger.kernel.org, ebiederm@xmission.com To: "Michael S. Tsirkin" Return-path: In-Reply-To: <20120417102220.GC20905@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On 04/17/2012 06:22 PM, Michael S. Tsirkin wrote: > 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; Yes, It's more is simpler.