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,URIBL_BLOCKED, 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 C0821C3A5A5 for ; Tue, 3 Sep 2019 06:06:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 965F92173E for ; Tue, 3 Sep 2019 06:06:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725956AbfICGGh (ORCPT ); Tue, 3 Sep 2019 02:06:37 -0400 Received: from mx1.redhat.com ([209.132.183.28]:57806 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725848AbfICGGh (ORCPT ); Tue, 3 Sep 2019 02:06:37 -0400 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id A2EDB10C6970; Tue, 3 Sep 2019 06:06:36 +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 41C0819D70; Tue, 3 Sep 2019 06:06:29 +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> <4a5d84b7-f3cb-c4e1-d6fe-28d186a551ee@redhat.com> <5D6DFD57.7020905@huawei.com> From: Jason Wang Message-ID: <71e17457-d4bc-15be-dfb3-d0a977fd7556@redhat.com> Date: Tue, 3 Sep 2019 14:06:22 +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: <5D6DFD57.7020905@huawei.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.65]); Tue, 03 Sep 2019 06:06:36 +0000 (UTC) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 2019/9/3 下午1:42, Yang Yingliang wrote: > > > On 2019/9/3 11:03, Jason Wang wrote: >> >> 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? > Yes, but it can't fix the UAF problem. Well, it looks to me that the dev_put() in tun_put() won't release the device in this case. Thanks >> >> Thanks >> >> >>> >>>> >>>> Thanks >>>> >>>> >>>>> Thanks, >>>>> Yang >>>>> >>>>>> >>>>>> Thanks >>>>>> >>>>>> . >>>>>> >>>>> >>>>> >>>> >>>> . >>>> >>> >>> >> >> . >> > >