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=-16.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 8E21DC433EF for ; Thu, 16 Sep 2021 13:55:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 76D3461056 for ; Thu, 16 Sep 2021 13:55:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237207AbhIPN4Y (ORCPT ); Thu, 16 Sep 2021 09:56:24 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:40329 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238063AbhIPN4X (ORCPT ); Thu, 16 Sep 2021 09:56:23 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1631800502; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=O5MT7htep4lfFb5DF7TWazpr34VmiixYifF4+r3+XCo=; b=iOGAzUsMlmbqmiM+CnTPp4eCK3EbQtycFctwYVbQ9vnxZXWkdYfKZ+HYtP89ZNNWJsPIEv zHHQIQHFtAgY9fpFt/kKBtTC5j9Z6Myo3nrnKxl2fye56RC29iBsGPwhoM0w31CeP3ANuT WVAggWcH3/fnW1qfFCT66YYyLTxLhg4= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-368-iEVy8uiXOMe8szfMmGzbTA-1; Thu, 16 Sep 2021 09:55:01 -0400 X-MC-Unique: iEVy8uiXOMe8szfMmGzbTA-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id EF79C802947; Thu, 16 Sep 2021 13:54:59 +0000 (UTC) Received: from T590 (ovpn-12-89.pek2.redhat.com [10.72.12.89]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 77A675C1D5; Thu, 16 Sep 2021 13:54:49 +0000 (UTC) Date: Thu, 16 Sep 2021 21:55:01 +0800 From: Ming Lei To: "yukuai (C)" Cc: josef@toxicpanda.com, axboe@kernel.dk, hch@infradead.org, linux-block@vger.kernel.org, nbd@other.debian.org, linux-kernel@vger.kernel.org, yi.zhang@huawei.com Subject: Re: [patch v8 7/7] nbd: fix uaf in nbd_handle_reply() Message-ID: References: <20210916093350.1410403-1-yukuai3@huawei.com> <20210916093350.1410403-8-yukuai3@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org 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. Thanks, Ming