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[23.128.96.18]) by mx.google.com with ESMTP id a4si2911632ilt.54.2021.09.16.07.08.26; Thu, 16 Sep 2021 07:09:07 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=huawei.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238163AbhIPOHK (ORCPT + 99 others); Thu, 16 Sep 2021 10:07:10 -0400 Received: from szxga02-in.huawei.com ([45.249.212.188]:9888 "EHLO szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235474AbhIPOHJ (ORCPT ); Thu, 16 Sep 2021 10:07:09 -0400 Received: from dggemv704-chm.china.huawei.com (unknown [172.30.72.55]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4H9Jf6474tz8yPn; Thu, 16 Sep 2021 22:01:18 +0800 (CST) Received: from dggema762-chm.china.huawei.com (10.1.198.204) by dggemv704-chm.china.huawei.com (10.3.19.47) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256) id 15.1.2308.8; Thu, 16 Sep 2021 22:05:46 +0800 Received: from [10.174.176.73] (10.174.176.73) by dggema762-chm.china.huawei.com (10.1.198.204) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.2308.8; Thu, 16 Sep 2021 22:05:45 +0800 Subject: Re: [patch v8 7/7] nbd: fix uaf in nbd_handle_reply() To: Ming Lei CC: , , , , , , References: <20210916093350.1410403-1-yukuai3@huawei.com> <20210916093350.1410403-8-yukuai3@huawei.com> From: "yukuai (C)" Message-ID: <66441ad9-629e-e50b-5d81-67edb79e51f2@huawei.com> Date: Thu, 16 Sep 2021 22:05:44 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="gbk"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.176.73] X-ClientProxiedBy: dggems703-chm.china.huawei.com (10.3.19.180) To dggema762-chm.china.huawei.com (10.1.198.204) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021/09/16 21:55, Ming Lei write: > On Thu, Sep 16, 2021 at 09:10:37PM +0800, yukuai (C) wrote: >> On 2021/09/16 20:58, Ming Lei wrote: >>> On Thu, Sep 16, 2021 at 05:33:50PM +0800, Yu Kuai wrote: >>>> There is a problem that nbd_handle_reply() might access freed request: >>>> >>>> 1) At first, a normal io is submitted and completed with scheduler: >>>> >>>> internel_tag = blk_mq_get_tag -> get tag from sched_tags >>>> blk_mq_rq_ctx_init >>>> sched_tags->rq[internel_tag] = sched_tag->static_rq[internel_tag] >>>> ... >>>> blk_mq_get_driver_tag >>>> __blk_mq_get_driver_tag -> get tag from tags >>>> tags->rq[tag] = sched_tag->static_rq[internel_tag] >>>> >>>> So, both tags->rq[tag] and sched_tags->rq[internel_tag] are pointing >>>> to the request: sched_tags->static_rq[internal_tag]. Even if the >>>> io is finished. >>>> >>>> 2) nbd server send a reply with random tag directly: >>>> >>>> recv_work >>>> nbd_handle_reply >>>> blk_mq_tag_to_rq(tags, tag) >>>> rq = tags->rq[tag] >>>> >>>> 3) if the sched_tags->static_rq is freed: >>>> >>>> blk_mq_sched_free_requests >>>> blk_mq_free_rqs(q->tag_set, hctx->sched_tags, i) >>>> -> step 2) access rq before clearing rq mapping >>>> blk_mq_clear_rq_mapping(set, tags, hctx_idx); >>>> __free_pages() -> rq is freed here >>>> >>>> 4) Then, nbd continue to use the freed request in nbd_handle_reply >>>> >>>> Fix the problem by get 'q_usage_counter' before blk_mq_tag_to_rq(), >>>> thus request is ensured not to be freed because 'q_usage_counter' is >>>> not zero. >>>> >>>> Signed-off-by: Yu Kuai >>>> --- >>>> drivers/block/nbd.c | 14 ++++++++++++++ >>>> 1 file changed, 14 insertions(+) >>>> >>>> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c >>>> index 69dc5eac9ad3..b3a47fc6237f 100644 >>>> --- a/drivers/block/nbd.c >>>> +++ b/drivers/block/nbd.c >>>> @@ -825,6 +825,7 @@ static void recv_work(struct work_struct *work) >>>> work); >>>> struct nbd_device *nbd = args->nbd; >>>> struct nbd_config *config = nbd->config; >>>> + struct request_queue *q = nbd->disk->queue; >>>> struct nbd_sock *nsock; >>>> struct nbd_cmd *cmd; >>>> struct request *rq; >>>> @@ -835,7 +836,20 @@ static void recv_work(struct work_struct *work) >>>> if (nbd_read_reply(nbd, args->index, &reply)) >>>> break; >>>> + /* >>>> + * Grab .q_usage_counter so request pool won't go away, then no >>>> + * request use-after-free is possible during nbd_handle_reply(). >>>> + * If queue is frozen, there won't be any inflight requests, we >>>> + * needn't to handle the incoming garbage message. >>>> + */ >>>> + if (!percpu_ref_tryget(&q->q_usage_counter)) { >>>> + dev_err(disk_to_dev(nbd->disk), "%s: no io inflight\n", >>>> + __func__); >>>> + break; >>>> + } >>>> + >>>> cmd = nbd_handle_reply(nbd, args->index, &reply); >>>> + percpu_ref_put(&q->q_usage_counter); >>>> if (IS_ERR(cmd)) >>>> break; >>> >>> The refcount needs to be grabbed when completing the request because >>> the request may be completed from other code path, then the request pool >>> will be freed from that code path when the request is referred. >> >> Hi, >> >> The request can't complete concurrently, thus put ref here is safe. >> >> There used to be a commet here that I tried to explain it... It's fine >> to me to move it behind anyway. > > Never see such comment. cmd->lock isn't held here, so I believe > concurrent completion is possible here. > After patch 2, __test_and_clear_bit(NBD_CMD_INFLIGHT) must pass while cmd->lock is held before completing the request, thus request completion won't concurrent... Thanks, Kuai