From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 DC18D70836; Tue, 7 Jul 2026 04:18:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783397884; cv=none; b=iz1V46cyudpVAeLxIHByhGVs9DzvhWxxl/HsmUKu4RXila3Q1bXJEXBDc0kS6qWInTzHg/AVZVtKbQGHeDIRMbfcOaZBy85tnbHbd9Sa+kfTWM+UAO+J0smv4l+cYmEUS2OdB1kvqqkZzovTK9My17/b52gWCHnHN1LG/RTMlvQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783397884; c=relaxed/simple; bh=QF8mVjX8IIrE/53BB1Ev0Shy7PrSJ7cJTRxaJKnhcbc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=dMNDySVoOO5O3seRQXyT6gn8OfqTDPEX2zS6ml+7Ty0jnkNYPznsA3mWaSgfuzjzf5/aJh0y6Q42TRTy/SRaHNzu/zVs5D47mbww3WjY9mEz8CYetHwRpMx9AdQKUih86RUOnrcfqvLJD213OI/hBS7ybUi9Y2ff/Z/1zzjypEs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=cJt3gv+M; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="cJt3gv+M" Received: by smtp.kernel.org (Postfix) with ESMTPSA id BD6541F000E9; Tue, 7 Jul 2026 04:18:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783397883; bh=SNRxr4zQ6HOifpngaa6brHBRqw26BzuaHAbkvSeDAeU=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=cJt3gv+MyYvh9dBwqNiO6L+gHRpGI15cHu3O/3s1HirJgkjB7664f/dBL1NHNXRv7 faOZTO4RlKSfO1QON0TaqfEO8lkjZGRmzwwSfxhnnHlPzpeT5alYVaH0lU3QajH7fO hElcjsaIzJZZGKbwCsWZA/oRDwzOoG7iFDxqk2qVRXbNJ3mcbHVK/Ub8krYXfs4ZQO 9s8ynO32mOpkscjYBmciUy8ITYlOS21oOBJJpQssGQnULRtgpRuy2W+n9uVVixYBzA ahE4bzaSVGQfkqHUN+vPdSAWYakZN1H8ktjdW5E7ZiARnYwXb+o89mSSV9SPoYgdeO v5leB388HOdWQ== Message-ID: Date: Tue, 7 Jul 2026 13:18:00 +0900 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V2 3/6] null_blk: register configfs subsystem after creating default devices To: Zizhi Wo , axboe@kernel.dk, nilay@linux.ibm.com, linux-block@vger.kernel.org, kch@nvidia.com, johannes.thumshirn@wdc.com, kbusch@kernel.org, bvanassche@acm.org Cc: linux-kernel@vger.kernel.org, yangerkun@huawei.com, chengzhihao1@huawei.com, wozizhi@huawei.com References: <20260707025542.1299859-1-wozizhi@huaweicloud.com> <20260707025542.1299859-4-wozizhi@huaweicloud.com> Content-Language: en-US From: Damien Le Moal Organization: Western Digital Research In-Reply-To: <20260707025542.1299859-4-wozizhi@huaweicloud.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/7/26 11:55, Zizhi Wo wrote: > From: Zizhi Wo > > In null_init(), configfs_register_subsystem() currently runs before > register_blkdev(), so when null_blk is built as a module, a racing mkdir() > + poweron from userspace can reach null_add_dev() while null_major is still > 0. __add_disk() then hits WARN_ON(disk->minors) (major=0 with minors!=0) > and fails: > > [root@fedora ~]# [ 2366.521436] WARNING: block/genhd.c:476 at __add_disk+0x8a7/0xde0, > [ 2366.523552] Modules linked in: null_blk(+) nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib > [ 2366.529081] CPU: 26 UID: 0 PID: 1600 Comm: sh Not tainted 7.2.0-rc1+ #66 PREEMPT(full) > ...... > [ 2366.547251] Call Trace: > [ 2366.547575] > [ 2366.547831] ? _raw_spin_lock+0x84/0xe0 > [ 2366.548260] add_disk_fwnode+0x114/0x560 > [ 2366.548739] null_add_dev+0x102d/0x1b80 [null_blk] > [ 2366.549310] ? __pfx_null_add_dev+0x10/0x10 [null_blk] > [ 2366.549906] ? mutex_lock+0xde/0x1c0 > [ 2366.550361] ? __pfx_mutex_lock+0x10/0x10 > [ 2366.550827] nullb_device_power_store+0x1e7/0x280 [null_blk] > [ 2366.551499] ? __pfx_nullb_device_power_store+0x10/0x10 [null_blk] > [ 2366.552177] ? __kmalloc_cache_noprof+0x1f5/0x470 > [ 2366.552748] ? configfs_write_iter+0x35c/0x4e0 > [ 2366.553242] configfs_write_iter+0x286/0x4e0 > [ 2366.553787] vfs_write+0x52d/0xd00 > [ 2366.554169] ? __pfx_vfs_write+0x10/0x10 > [ 2366.554679] ? __pfx___css_rstat_updated+0x10/0x10 > [ 2366.555196] ? fdget_pos+0x1cf/0x4c0 > [ 2366.555649] ksys_write+0xfc/0x1d0 > ...... > > Additionally, the err_dev path destroys all devices on nullb_list while > configfs is still registered. If a racing mkdir() + poweron puts a user > device on the list, null_destroy_dev()->null_free_dev() kfrees the user > device's nullb_device but /sys/kernel/config/nullb/ is still > reachable. Any userspace access to the item will trigger a UAF. > > For simplicity, move configfs_register_subsystem() to the end to solve > the problems above. This also mirrors null_exit(). > > Fixes: 3bf2bd20734e ("nullb: add configfs interface") > Signed-off-by: Zizhi Wo Looks good. Reviewed-by: Damien Le Moal -- Damien Le Moal Western Digital Research