From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from canpmsgout07.his.huawei.com (canpmsgout07.his.huawei.com [113.46.200.222]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 022D13C942C; Fri, 18 Sep 2026 08:35:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=113.46.200.222 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789720511; cv=none; b=TkX3nipBSmpIbUP352FbkjJN6n6cecFn/UkdOR0tKkpXyYHu/E3wmpmsZjC5Cz4mEnEv56XEenvkpiTHviy0YAacpyfRqM+Z63P6+P2Zm0Wg4891fF8v507Zc/wDGtTqZOxTJw29eWMBzl2xewl+qt85MhTtYwf7mxCjVl7Kw1k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789720511; c=relaxed/simple; bh=8COvAdtMn3spnXyGgMVW42NNpWqP4tPV2ZEYwmjtTuA=; h=Subject:To:CC:References:From:Message-ID:Date:MIME-Version: In-Reply-To:Content-Type; b=MasQ9CsTgv2gHpFccQ2TkrhgP1HF+x0KSWVKLpeUnMnfQ381IH/Xk4vWrYCyJ2rdMPX6V5jFzA5bMTykdmHaNDhfCn4X4kCX3pGWDqeMir3jduBbOseQTMYoQ+BQA3JPUKVYHf+OsOAemUOc+8rlOEgIpylbSPOg3/N79MfOhDc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; dkim=pass (1024-bit key) header.d=huawei.com header.i=@huawei.com header.b=xKpFyfcQ; arc=none smtp.client-ip=113.46.200.222 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=huawei.com header.i=@huawei.com header.b="xKpFyfcQ" dkim-signature: v=1; a=rsa-sha256; d=huawei.com; s=dkim; c=relaxed/relaxed; q=dns/txt; h=From; bh=JVGWE/qK9v712s+HPMWX0MyEOLtqPkE26TNEv0rEr50=; b=xKpFyfcQwZKsvmbEx65fXN6GpNJkr+kZUUTmgLDVcKn0j2w4VgafJ6Nknr79K7SPBGpTDHdhh CNp1io2PgF5tgqJ3E/rhOrQt+DO7nDCOX8QflxK0YRdxEJm9ZJph/kG7mDDHd9LSrQx1f8+PhVu clCx4KWnDZAz8MK0kQYzSBY= Received: from mail.maildlp.com (unknown [172.19.163.214]) by canpmsgout07.his.huawei.com (SkyGuard) with ESMTPS id 4hmQdH74nGzLlSh; Fri, 18 Sep 2026 16:24:03 +0800 (CST) Received: from whupemo200011.china.huawei.com (unknown [7.152.185.179]) by mail.maildlp.com (Postfix) with ESMTPS id D534C4056C; Fri, 18 Sep 2026 16:35:03 +0800 (CST) Received: from [10.174.178.46] (10.174.178.46) by whupemo200011.china.huawei.com (7.152.185.179) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.45; Fri, 18 Sep 2026 16:35:02 +0800 Subject: Re: [PATCH v3] md: Fix the null-ptr-deref of 'mddev->private' while submitting IO To: Abd-Alrhman Masalkhi , , , , , CC: , , , References: <20260918070900.1945351-1-chengzhihao1@huawei.com> <249f987d-9d2d-8f5c-91dd-3af6baefe587@huawei.com> From: Zhihao Cheng Message-ID: <856a065c-38ef-08cd-7701-8f579212a1a3@huawei.com> Date: Fri, 18 Sep 2026 16:34:57 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: kwepems500002.china.huawei.com (7.221.188.17) To whupemo200011.china.huawei.com (7.152.185.179) 在 2026/9/18 16:20, Abd-Alrhman Masalkhi 写道: > On Fri, Sep 18, 2026 at 15:38 +0800, Zhihao Cheng wrote: >> 在 2026/9/18 15:29, Abd-Alrhman Masalkhi 写道: >>> >>> Hi Zhihao, >>> >>> On Fri, Sep 18, 2026 at 15:09 +0800, Zhihao Cheng wrote: >>>> Concurrent processes md_stop and IO submitting could trigger a >>>> null-ptr-deref of 'mddev->private': >>>> >>>> BUG: kernel NULL pointer dereference, address: 0000000000000070 >>>> RIP: 0010:_wait_barrier+0x2f/0x250 >>>> Call Trace: >>>> raid1_make_request+0x150/0xf50 >>>> md_handle_request+0x104/0x530 >>>> md_submit_bio+0x76/0x130 >>>> submit_bio+0xdd/0x250 >>>> submit_bio_wait+0x1f/0x40 >>>> __blkdev_direct_IO_simple+0x1f6/0x370 >>>> blkdev_write_iter+0x3b2/0x520 >>>> ksys_write+0x7d/0x190 >>>> >>>> P1 >>>> fd = open(/dev/md0, O_RDWR) >>>> P2 (forked from P1, fd' <= fd) >>>> write(fd) >>>> submit_bio >>>> md_handle_request >>>> raid1_make_request >>>> raid1_write_request >>>> ioctl(fd, STOP_ARRAY) >>>> mddev_set_closing_and_sync_blockdev >>>> // check passed, mddev->openers = 1, >>>> // because md_open() is only called >>>> // once in P1->open >>>> do_md_stop >>>> __md_stop >>>> mddev->private = NULL >>>> >>>> conf = mddev->private // NULL >>>> wait_barrier(conf, sector) // null-ptr-deref ! >>>> >>>> It is a common problem for raid0/1/10/5, and __md_stop could be triggered >>>> by several paths(eg. ioctl, sysfs, ->dtr). Fix it by replacing >>>> mddev_lock() with mddev_suspend_and_lock() for all __md_stop() callers. >>>> The caller dm_table_destroy() is guaranteed being invoked with device >>>> suspended, so raid_dtr() could keep using mddev_lock_nointr(). >>>> The caller array_state_store() is guaranteed by the check >>>> mddev_set_closing_and_sync_blockdev(mddev, 0). For example, someone open >>>> /dev/mdx, write something and close /dev/mdx, it won't trigger the >>>> problem, all dirty pages can be flushed before mddev->openers decrement. >>>> Besides, fail the submitting IO in md_handle_request() if the >>>> 'mddev->pers' becomes NULL. >>>> >>>> Fetch a reproducer in https://bugzilla.kernel.org/show_bug.cgi?id=222020 >>>> >>>> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") >>>> Reported-by: syzbot+3fe892ea5fc292e1353f@syzkaller.appspotmail.com >>>> Closes: https://syzkaller.appspot.com/bug?extid=3fe892ea5fc292e1353f >>>> Signed-off-by: Zhihao Cheng >>>> --- >>>> v1->v2: >>>> 1. Add 'mddev->pers != NULL' check before make_request >>>> 2. Delete dm-raid caller(->dtr) modifications >>>> 3. Move memalloc_noio_restore after mddev_unlock_and_resume >>>> v2->v3: >>>> 1. Remove modifications in array_state_store() >>>> 2. update commit msg >>>> drivers/md/md.c | 15 +++++++++++++++ >>>> 1 file changed, 15 insertions(+) >>>> >>>> diff --git a/drivers/md/md.c b/drivers/md/md.c >>>> index 680b34a63cb3..e73338c26d53 100644 >>>> --- a/drivers/md/md.c >>>> +++ b/drivers/md/md.c >>>> @@ -414,6 +414,20 @@ bool md_handle_request(struct mddev *mddev, struct bio *bio) >>>> if (!percpu_ref_tryget_live(&mddev->active_io)) >>>> goto check_suspended; >>>> } >>>> + if (!mddev->pers) { >>> Isn't this case already handled by md_submit_bio(). take a look in >>> md_submit_bio() >> Hi,Abd-Alrhman >> I understand that 'mddev == NULL || mddev->pers == NULL' in >> md_submit_bio() is a qiuck check, there still exists a small race window: >> P1 P2 >> md_submit_bio >> if (mddev == NULL || mddev->pers == NULL) >> md_ioctl >> mddev_suspend_and_lock >> do_md_stop->__md_stop >> // set mddev->pers/private as NULL >> mddev_unlock_and_resume >> md_handle_request >> if (is_suspended(mddev, bio)) >> percpu_ref_tryget_live(&mddev->active_io) >> mddev->pers // null-ptr-deref > > It makes sense. It would solve only the null pointer reference, but I > see another issue. Look at the comment before calling > mddev_set_closing_and_sync_blockdev() in md_ioctl(). it says "Need to > flush page cache, and ensure no-one else opens and writes". The > suspending happens after flushing the page cache, in this case, > there might be other writes in-flight. At present, the current implementation does not align with the expected annotations. Yu Kai privately gave me a feasible suggestion, which is to have md_ioctl operate on a character device(like /dev/mapper/control) instead of an md block device. This fix patch will serve as a temporary solution before the official implementation is merged. By the way, I don't have much time to implment it, do you have time to deal with the official solution? > >>> >>>> + /* >>>> + * The __md_stop() sets 'mddev->private' to NULL during >>>> + * the IO submitting, check 'mddev->pers' before the IO >>>> + * being processed by specific driver to avoid the >>>> + * null-ptr-deref of 'mddev->'. The check is >>>> + * safe because the IO has got the 'mddev->active_io' >>>> + * reference, and all __md_stop() callers will wait for >>>> + * the reference to be zero. >>>> + */ >>>> + bio_io_error(bio); >>>> + percpu_ref_put(&mddev->active_io); >>>> + return true; >>>> + } >>>> if (!mddev->pers->make_request(mddev, bio)) { >>>> percpu_ref_put(&mddev->active_io); >>>> if (mddev_is_dm(mddev) && mddev->pers->prepare_suspend) >>>> @@ -8299,6 +8313,7 @@ static bool md_ioctl_need_suspend(unsigned int cmd) >>>> case HOT_REMOVE_DISK: >>>> case SET_BITMAP_FILE: >>>> case SET_ARRAY_INFO: >>>> + case STOP_ARRAY: >>>> return true; >>>> default: >>>> return false; >>>> -- >>>> 2.52.0 >>>> >>> >> >