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 AE59FC3A5A5 for ; Tue, 3 Sep 2019 05:43:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 87ED8216C8 for ; Tue, 3 Sep 2019 05:43:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726738AbfICFnC (ORCPT ); Tue, 3 Sep 2019 01:43:02 -0400 Received: from szxga07-in.huawei.com ([45.249.212.35]:57272 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725878AbfICFnC (ORCPT ); Tue, 3 Sep 2019 01:43:02 -0400 Received: from DGGEMS409-HUB.china.huawei.com (unknown [172.30.72.58]) by Forcepoint Email with ESMTP id A19E1EBA214DD7CEB273; Tue, 3 Sep 2019 13:42:59 +0800 (CST) Received: from [127.0.0.1] (10.133.205.80) by DGGEMS409-HUB.china.huawei.com (10.3.19.209) with Microsoft SMTP Server id 14.3.439.0; Tue, 3 Sep 2019 13:42:48 +0800 Subject: Re: [PATCH v3] tun: fix use-after-free when register netdev failed To: Jason Wang 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> CC: David Miller , , eric dumazet , xiyou wangcong , From: Yang Yingliang Message-ID: <5D6DFD57.7020905@huawei.com> Date: Tue, 3 Sep 2019 13:42:47 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1 MIME-Version: 1.0 In-Reply-To: <4a5d84b7-f3cb-c4e1-d6fe-28d186a551ee@redhat.com> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.133.205.80] X-CFilter-Loop: Reflected Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org 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. > > Thanks > > >> >>> >>> Thanks >>> >>> >>>> Thanks, >>>> Yang >>>> >>>>> >>>>> Thanks >>>>> >>>>> . >>>>> >>>> >>>> >>> >>> . >>> >> >> > > . >