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=-16.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,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 AB4BCC433F5 for ; Thu, 16 Sep 2021 08:47:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 960D96120C for ; Thu, 16 Sep 2021 08:47:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235186AbhIPIsm (ORCPT ); Thu, 16 Sep 2021 04:48:42 -0400 Received: from szxga02-in.huawei.com ([45.249.212.188]:15424 "EHLO szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235249AbhIPIsj (ORCPT ); Thu, 16 Sep 2021 04:48:39 -0400 Received: from dggemv711-chm.china.huawei.com (unknown [172.30.72.57]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4H99b11KqXzRFwZ; Thu, 16 Sep 2021 16:43:09 +0800 (CST) Received: from dggema762-chm.china.huawei.com (10.1.198.204) by dggemv711-chm.china.huawei.com (10.1.198.66) 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 16:47:09 +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 16:47:09 +0800 Subject: Re: [PATCH v7 6/6] nbd: fix uaf in nbd_handle_reply() To: Ming Lei CC: , , , , , , References: <20210915092010.2087371-1-yukuai3@huawei.com> <20210915092010.2087371-7-yukuai3@huawei.com> From: "yukuai (C)" Message-ID: Date: Thu, 16 Sep 2021 16:47:08 +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-block@vger.kernel.org On 2021/09/16 16:04, Ming Lei wrote: > On Wed, Sep 15, 2021 at 05:20:10PM +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 | 18 ++++++++++++++++++ >> 1 file changed, 18 insertions(+) >> >> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c >> index 9a7bbf8ebe74..3e8b70b5d4f9 100644 >> --- a/drivers/block/nbd.c >> +++ b/drivers/block/nbd.c >> @@ -824,6 +824,7 @@ 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; >> @@ -834,7 +835,24 @@ static void recv_work(struct work_struct *work) >> if (nbd_read_reply(nbd, args->index, &reply)) >> break; >> >> + /* >> + * Grab ref of q_usage_counter can prevent request being freed >> + * during nbd_handle_reply(). If q_usage_counter is zero, then >> + * no request is inflight, which means something is wrong since >> + * we expect to find a request to complete here. >> + */ > > The above comment is wrong, the purpose is simply for avoiding request > pool freed, such as elevator switching won't happen once > ->q_usage_counter is grabbed. So no any request UAF can be triggered > when calling into nbd_handle_reply(). Do you mean the comment about q_usage_counter is zero is wrong ? > >> + 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); >> + /* >> + * It's safe to drop ref before request completion, inflight >> + * request will ensure q_usage_counter won't be zero. >> + */ > > The above comment is useless actually. Will remove the comments. Thanks, Kuai >