From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 549E9C3A5A7 for ; Tue, 3 Sep 2019 03:07:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2E6D222CF7 for ; Tue, 3 Sep 2019 03:07:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726157AbfICDDm (ORCPT ); Mon, 2 Sep 2019 23:03:42 -0400 Received: from mx1.redhat.com ([209.132.183.28]:41496 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725816AbfICDDl (ORCPT ); Mon, 2 Sep 2019 23:03:41 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 01423307CDFC; Tue, 3 Sep 2019 03:03:41 +0000 (UTC) Received: from [10.72.12.109] (ovpn-12-109.pek2.redhat.com [10.72.12.109]) by smtp.corp.redhat.com (Postfix) with ESMTP id 67749608AB; Tue, 3 Sep 2019 03:03:37 +0000 (UTC) Subject: Re: [PATCH v3] tun: fix use-after-free when register netdev failed To: Yang Yingliang Cc: David Miller , netdev@vger.kernel.org, eric dumazet , xiyou wangcong , weiyongjun1@huawei.com References: <1566221479-16094-1-git-send-email-yangyingliang@huawei.com> <20190819.182522.414877916903078544.davem@davemloft.net> <5D5E3133.2070108@huawei.com> <5D5E90C3.50306@huawei.com> <1676209666.10068041.1566529505528.JavaMail.zimbra@redhat.com> <5D5FB3B6.5080800@huawei.com> <1be732b2-6eda-4ea6-772d-780694557910@redhat.com> <5D6DC5BF.5020009@huawei.com> From: Jason Wang Message-ID: <4a5d84b7-f3cb-c4e1-d6fe-28d186a551ee@redhat.com> Date: Tue, 3 Sep 2019 11:03:36 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <5D6DC5BF.5020009@huawei.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.49]); Tue, 03 Sep 2019 03:03:41 +0000 (UTC) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 2019/9/3 上午9:45, Yang Yingliang wrote: > > > On 2019/9/2 13:32, Jason Wang wrote: >> >> On 2019/8/23 下午5:36, Yang Yingliang wrote: >>> >>> >>> On 2019/8/23 11:05, Jason Wang wrote: >>>> ----- Original Message ----- >>>>> >>>>> On 2019/8/22 14:07, Yang Yingliang wrote: >>>>>> >>>>>> On 2019/8/22 10:13, Jason Wang wrote: >>>>>>> On 2019/8/20 上午10:28, Jason Wang wrote: >>>>>>>> On 2019/8/20 上午9:25, David Miller wrote: >>>>>>>>> From: Yang Yingliang >>>>>>>>> Date: Mon, 19 Aug 2019 21:31:19 +0800 >>>>>>>>> >>>>>>>>>> Call tun_attach() after register_netdevice() to make sure >>>>>>>>>> tfile->tun >>>>>>>>>> is not published until the netdevice is registered. So the >>>>>>>>>> read/write >>>>>>>>>> thread can not use the tun pointer that may freed by >>>>>>>>>> free_netdev(). >>>>>>>>>> (The tun and dev pointer are allocated by alloc_netdev_mqs(), >>>>>>>>>> they >>>>>>>>>> can >>>>>>>>>> be freed by netdev_freemem().) >>>>>>>>> register_netdevice() must always be the last operation in the >>>>>>>>> order of >>>>>>>>> network device setup. >>>>>>>>> >>>>>>>>> At the point register_netdevice() is called, the device is >>>>>>>>> visible >>>>>>>>> globally >>>>>>>>> and therefore all of it's software state must be fully >>>>>>>>> initialized and >>>>>>>>> ready for us. >>>>>>>>> >>>>>>>>> You're going to have to find another solution to these problems. >>>>>>>> >>>>>>>> The device is loosely coupled with sockets/queues. Each side is >>>>>>>> allowed to be go away without caring the other side. So in this >>>>>>>> case, there's a small window that network stack think the >>>>>>>> device has >>>>>>>> one queue but actually not, the code can then safely drop them. >>>>>>>> Maybe it's ok here with some comments? >>>>>>>> >>>>>>>> Or if not, we can try to hold the device before tun_attach and >>>>>>>> drop >>>>>>>> it after register_netdevice(). >>>>>>> >>>>>>> Hi Yang: >>>>>>> >>>>>>> I think maybe we can try to hold refcnt instead of playing real num >>>>>>> queues here. Do you want to post a V4? >>>>>> I think the refcnt can prevent freeing the memory in this case. >>>>>> When register_netdevice() failed, free_netdev() will be called >>>>>> directly, >>>>>> dev->pcpu_refcnt and dev are freed without checking refcnt of dev. >>>>> How about using patch-v1 that using a flag to check whether the >>>>> device >>>>> registered successfully. >>>>> >>>> As I said, it lacks sufficient locks or barriers. To be clear, I meant >>>> something like (compile-test only): >>>> >>>> diff --git a/drivers/net/tun.c b/drivers/net/tun.c >>>> index db16d7a13e00..e52678f9f049 100644 >>>> --- a/drivers/net/tun.c >>>> +++ b/drivers/net/tun.c >>>> @@ -2828,6 +2828,7 @@ static int tun_set_iff(struct net *net, >>>> struct file *file, struct ifreq *ifr) >>>>                                (ifr->ifr_flags & TUN_FEATURES); >>>>                    INIT_LIST_HEAD(&tun->disabled); >>>> +               dev_hold(dev); >>>>                  err = tun_attach(tun, file, false, ifr->ifr_flags >>>> & IFF_NAPI, >>>>                                   ifr->ifr_flags & IFF_NAPI_FRAGS); >>>>                  if (err < 0) >>>> @@ -2836,6 +2837,7 @@ static int tun_set_iff(struct net *net, >>>> struct file *file, struct ifreq *ifr) >>>>                  err = register_netdevice(tun->dev); >>>>                  if (err < 0) >>>>                          goto err_detach; >>>> +               dev_put(dev); >>>>          } >>>>            netif_carrier_on(tun->dev); >>>> @@ -2852,11 +2854,13 @@ static int tun_set_iff(struct net *net, >>>> struct file *file, struct ifreq *ifr) >>>>          return 0; >>>>     err_detach: >>>> +       dev_put(dev); >>>>          tun_detach_all(dev); >>>>          /* register_netdevice() already called tun_free_netdev() */ >>>>          goto err_free_dev; >>>>     err_free_flow: >>>> +       dev_put(dev); >>>>          tun_flow_uninit(tun); >>>>          security_tun_dev_free_security(tun->security); >>>>   err_free_stat: >>>> >>>> What's your thought? >>> >>> The dev pointer are freed without checking the refcount in >>> free_netdev() called by err_free_dev >>> >>> path, so I don't understand how the refcount protects this pointer. >>> >> >> The refcount are guaranteed to be zero there, isn't it? > No, it's not. > > err_free_dev: >         free_netdev(dev); > > void free_netdev(struct net_device *dev) > { > ... >         /* pcpu_refcnt can be freed without checking refcount */ >         free_percpu(dev->pcpu_refcnt); >         dev->pcpu_refcnt = NULL; > >         /*  Compatibility with error handling in drivers */ >         if (dev->reg_state == NETREG_UNINITIALIZED) { >                 /* dev can be freed without checking refcount */ >                 netdev_freemem(dev); >                 return; >         } > ... > } Right, but what I meant is in my patch, when code reaches free_netdev() the refcnt is zero. What did I miss? Thanks > >> >> Thanks >> >> >>> Thanks, >>> Yang >>> >>>> >>>> Thanks >>>> >>>> . >>>> >>> >>> >> >> . >> > >