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 808F7C433EF for ; Wed, 13 Apr 2022 05:22:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232392AbiDMFY2 (ORCPT ); Wed, 13 Apr 2022 01:24:28 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33260 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232101AbiDMFY1 (ORCPT ); Wed, 13 Apr 2022 01:24:27 -0400 Received: from mail-ej1-x632.google.com (mail-ej1-x632.google.com [IPv6:2a00:1450:4864:20::632]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0FB664F9D2 for ; Tue, 12 Apr 2022 22:22:05 -0700 (PDT) Received: by mail-ej1-x632.google.com with SMTP id s18so1720412ejr.0 for ; Tue, 12 Apr 2022 22:22:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ionos.com; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=cdeKgFpJvLEHvH552w4sygZi2El7+LZAqARF9ocqxh0=; b=fzSQIPniJYDY30ggsApkSEApxWiKMzzhpvMzBJS8rVogyZ8l60Y3vB8cBRQNiedonu +Wacz2pWLsJ5+U6hyR6/tWngywcmoyvySanIDj1DsHAAwiWJKGP/M4q8HAVJ1gmL6Rj1 VWiAAKJfB4I/tJEB3nmvF7/GWitViZh+XBv2mPHVVcGe0E2f+gmkH0WNR0Y1VTYv+IDJ i3RIGrkWN4lWO8NZ4rLnk9pdXS67dRI5bEWxnj1aqvrnhaQpe1Ieh5RdtMK9xGFI+mwe ng/YyaEBL2/o1XadAYEeZMqgHWBb9DJxtQgbnrxjq1KgxpNbMDpMFQqes7MvHZKalF56 VsIg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=cdeKgFpJvLEHvH552w4sygZi2El7+LZAqARF9ocqxh0=; b=JZg9/C3lN2WeSs/BtK/MtVvCQAv06apI/lxc4LuKXDy4zHMWHBbGjBRsRguGXZXU3+ JwwwzuBRxR9NFT3si26tZ/StjY65jwjVvZTC9XfZyXHyhqwm4oyAqtI6tr+m6th+oyBL kjiZ1hDNpuU530akCWzZ7WDU/N6GmvXrAYF1nqVRy6nsFshE0a0LrtBs6lOvdAyNKUFH lRhkL3KAoxIjKopNVNTjKv/EPAY8ps+UANt+38qdftQloHrlKBRnbrj+Pw7iz6FAws3J Jl/y411jGYzlUewdgykXJ8JbWMWLnn4B0pNDcodi/hOVRysckohsz1H7/NTzssa0KG/H lWHg== X-Gm-Message-State: AOAM531v95ovFCjbBU8sl2qcWX5RNXzzpI/GcoecW58pJGJCaNlha+SB kOAGhhgicrIlWg28/hEfc3upNZRkKpGpAkd3Myspsg== X-Google-Smtp-Source: ABdhPJyND6FFswxqjiYBspCBqGztxwB0CpNUo2ZkpeAMIz1dajivfwDzobMyhVC8cy3Rv+CQe34QgULBKeOvwZts0EA= X-Received: by 2002:a17:906:d552:b0:6e8:4ee4:748 with SMTP id cr18-20020a170906d55200b006e84ee40748mr22356949ejc.58.1649827323519; Tue, 12 Apr 2022 22:22:03 -0700 (PDT) MIME-Version: 1.0 References: <55006f3b-9571-9167-eaf0-6a2caec747ad@I-love.SAKURA.ne.jp> In-Reply-To: <55006f3b-9571-9167-eaf0-6a2caec747ad@I-love.SAKURA.ne.jp> From: Jinpu Wang Date: Wed, 13 Apr 2022 07:21:52 +0200 Message-ID: Subject: Re: [PATCH] block/rnbd: client: avoid flush_workqueue(system_long_wq) usage To: Tetsuo Handa Cc: "Md. Haris Iqbal" , Jens Axboe , linux-block Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org Hi Tetsuo, On Wed, Apr 13, 2022 at 12:18 AM Tetsuo Handa wrote: > > On 2022/04/12 22:46, Tetsuo Handa wrote: > > Flushing system-wide workqueues is dangerous and will be forbidden. > > > > Since system_long_wq is used only inside rnbd_destroy_sessions(), > > let's use list_head than creating a local workqueue for tracking > > work_struct to flush. > > > > Link: https://lkml.kernel.org/r/49925af7-78a8-a3dd-bce6-cfc02e1a9236@I-love.SAKURA.ne.jp > > > > Signed-off-by: Tetsuo Handa > > --- > > Notice: This patch is only compile tested. Please test before applying. > > > > drivers/block/rnbd/rnbd-clt.c | 5 ++++- > > drivers/block/rnbd/rnbd-clt.h | 1 + > > 2 files changed, 5 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/block/rnbd/rnbd-clt.c b/drivers/block/rnbd/rnbd-clt.c > > index b66e8840b94b..b14e7c15133e 100644 > > --- a/drivers/block/rnbd/rnbd-clt.c > > +++ b/drivers/block/rnbd/rnbd-clt.c > > @@ -1730,6 +1730,7 @@ static void rnbd_destroy_sessions(void) > > { > > struct rnbd_clt_session *sess, *sn; > > struct rnbd_clt_dev *dev, *tn; > > + LIST_HEAD(list); > > > > /* Firstly forbid access through sysfs interface */ > > rnbd_clt_destroy_sysfs_files(); > > @@ -1762,11 +1763,13 @@ static void rnbd_destroy_sessions(void) > > */ > > INIT_WORK(&dev->unmap_on_rmmod_work, unmap_device_work); > > queue_work(system_long_wq, &dev->unmap_on_rmmod_work); > > + list_add_tail(&dev->unmap_on_rmmod_list, &list); > > } > > rnbd_clt_put_sess(sess); > > } > > /* Wait for all scheduled unmap works */ > > - flush_workqueue(system_long_wq); > > + list_for_each_entry(dev, &list, unmap_on_rmmod_list) > > + flush_work(&dev->unmap_on_rmmod_work); > > Since kfree(dev) might be called from unmap_device_work(), this seems unsafe. > We need rnbd_clt_get_dev() before queue_work() and rnbd_clt_put_dev() after flush_work() > in order to make dev->unmap_on_rmmod_list traversal safe... you are right, unmap_device_work could free the dev structure, lead to UAF. simply add rnbd_clt_get_dev and put_dev will lead to following WARN_ON to be triggered. > > > WARN_ON(!list_empty(&sess_list)); > > } I feel the simple approach is to replace the gloable system_long_wq with a local workqueue for rnbd_client. Thanks! > > > > diff --git a/drivers/block/rnbd/rnbd-clt.h b/drivers/block/rnbd/rnbd-clt.h > > index 2e2e8c4a85c1..a6d704abda61 100644 > > --- a/drivers/block/rnbd/rnbd-clt.h > > +++ b/drivers/block/rnbd/rnbd-clt.h > > @@ -136,6 +136,7 @@ struct rnbd_clt_dev { > > char *blk_symlink_name; > > refcount_t refcount; > > struct work_struct unmap_on_rmmod_work; > > + struct list_head unmap_on_rmmod_list; > > }; > > > > /* rnbd-clt.c */ >