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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D303BC433F5 for ; Wed, 22 Dec 2021 03:12:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238712AbhLVDMu (ORCPT ); Tue, 21 Dec 2021 22:12:50 -0500 Received: from szxga02-in.huawei.com ([45.249.212.188]:29279 "EHLO szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238670AbhLVDMt (ORCPT ); Tue, 21 Dec 2021 22:12:49 -0500 Received: from kwepemi100001.china.huawei.com (unknown [172.30.72.56]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4JJdfc1ff6zbjM8; Wed, 22 Dec 2021 11:12:24 +0800 (CST) Received: from kwepemm600009.china.huawei.com (7.193.23.164) by kwepemi100001.china.huawei.com (7.221.188.215) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2308.20; Wed, 22 Dec 2021 11:12:47 +0800 Received: from [10.174.176.73] (10.174.176.73) by kwepemm600009.china.huawei.com (7.193.23.164) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2308.20; Wed, 22 Dec 2021 11:12:46 +0800 Subject: Re: [PATCH 4/4] block, bfq: update pos_root for idle bfq_queue in bfq_bfqq_move() To: Jan Kara CC: , , , , , , , , References: <20211221032135.878550-1-yukuai3@huawei.com> <20211221032135.878550-5-yukuai3@huawei.com> <20211221115001.GD24748@quack2.suse.cz> From: "yukuai (C)" Message-ID: <6ca1e924-47fa-b94e-598c-69a9549eb68e@huawei.com> Date: Wed, 22 Dec 2021 11:12:45 +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: <20211221115001.GD24748@quack2.suse.cz> Content-Type: text/plain; charset="gbk"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.176.73] X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) To kwepemm600009.china.huawei.com (7.193.23.164) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org ÔÚ 2021/12/21 19:50, Jan Kara дµÀ: > On Tue 21-12-21 11:21:35, Yu Kuai wrote: >> During code review, we found that if bfqq is not busy in >> bfq_bfqq_move(), bfq_pos_tree_add_move() won't be called for the bfqq, >> thus bfqq->pos_root still points to the old bfqg. However, the ref >> that bfqq hold for the old bfqg will be released, so it's possible >> that the old bfqg can be freed. This is problematic because the freed >> bfqg can still be accessed by bfqq->pos_root. >> >> Fix the problem by calling bfq_pos_tree_add_move() for idle bfqq >> as well. >> >> Fixes: e21b7a0b9887 ("block, bfq: add full hierarchical scheduling and cgroups support") >> Signed-off-by: Yu Kuai > > I'm just wondering, how can it happen that !bfq_bfqq_busy() queue is in > pos_tree? Because bfq_remove_request() takes care to remove bfqq from the > pos_tree... Hi, It's right this is not a problem in common case. The problem seems to relate to queue merging and task migration. Because I once reporduced it with the same reporducer for the problem that offlined bfqg can be inserted into service tree. The uaf is exactly in bfq_remove_request->rb_rease(). However I didn't save the stack... I guess this is because bfq_del_bfqq_busy() is called from bfq_release_process_ref(), and queue merging prevert sunch bfqq to be freed, thus such bfqq is not in service tree, and it's pos_root can point to the old bfqg after bfq_bic_update_cgroup->bfq_bfqq_move. I haven't confirmed this, however, this patch itself only cleared bfqq->pos_root for idle bfqq, there should be no harm. Thanks, Kuai > > Honza > >> --- >> block/bfq-cgroup.c | 14 +++++++++----- >> 1 file changed, 9 insertions(+), 5 deletions(-) >> >> diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c >> index 8e8cf6b3d946..822dd28ecf53 100644 >> --- a/block/bfq-cgroup.c >> +++ b/block/bfq-cgroup.c >> @@ -677,7 +677,6 @@ void bfq_bfqq_move(struct bfq_data *bfqd, struct bfq_queue *bfqq, >> bfq_deactivate_bfqq(bfqd, bfqq, false, false); >> else if (entity->on_st_or_in_serv) >> bfq_put_idle_entity(bfq_entity_service_tree(entity), entity); >> - bfqg_and_blkg_put(old_parent); >> >> if (entity->parent && >> entity->parent->last_bfqq_created == bfqq) >> @@ -690,11 +689,16 @@ void bfq_bfqq_move(struct bfq_data *bfqd, struct bfq_queue *bfqq, >> /* pin down bfqg and its associated blkg */ >> bfqg_and_blkg_get(bfqg); >> >> - if (bfq_bfqq_busy(bfqq)) { >> - if (unlikely(!bfqd->nonrot_with_queueing)) >> - bfq_pos_tree_add_move(bfqd, bfqq); >> + /* >> + * Don't leave the pos_root to old bfqg, since the ref to old bfqg will >> + * be released and the bfqg might be freed. >> + */ >> + if (unlikely(!bfqd->nonrot_with_queueing)) >> + bfq_pos_tree_add_move(bfqd, bfqq); >> + bfqg_and_blkg_put(old_parent); >> + >> + if (bfq_bfqq_busy(bfqq)) >> bfq_activate_bfqq(bfqd, bfqq); >> - } >> >> if (!bfqd->in_service_queue && !bfqd->rq_in_driver) >> bfq_schedule_dispatch(bfqd); >> -- >> 2.31.1 >>