From: Damien Le Moal <dlemoal@kernel.org>
To: Zizhi Wo <wozizhi@huaweicloud.com>,
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
Subject: Re: [PATCH V2 3/6] null_blk: register configfs subsystem after creating default devices
Date: Tue, 7 Jul 2026 13:18:00 +0900 [thread overview]
Message-ID: <ca15dc52-d2ee-4fef-8c3d-6b8425e7afb7@kernel.org> (raw)
In-Reply-To: <20260707025542.1299859-4-wozizhi@huaweicloud.com>
On 7/7/26 11:55, Zizhi Wo wrote:
> From: Zizhi Wo <wozizhi@huawei.com>
>
> 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] <TASK>
> [ 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/<name> 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 <wozizhi@huawei.com>
Looks good.
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
--
Damien Le Moal
Western Digital Research
next prev parent reply other threads:[~2026-07-07 4:18 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-07 2:55 [PATCH V2 0/6] null_blk: fix init/exit races, leaks and cleanup Zizhi Wo
2026-07-07 2:55 ` [PATCH V2 1/6] null_blk: use DEFINE_MUTEX for the file-scope mutex Zizhi Wo
2026-07-07 4:07 ` Damien Le Moal
2026-07-07 2:55 ` [PATCH V2 2/6] null_blk: give the file-scope mutex a descriptive name Zizhi Wo
2026-07-07 4:16 ` Damien Le Moal
2026-07-07 6:24 ` Zizhi Wo
2026-07-07 6:28 ` Damien Le Moal
2026-07-07 6:45 ` Zizhi Wo
2026-07-07 2:55 ` [PATCH V2 3/6] null_blk: register configfs subsystem after creating default devices Zizhi Wo
2026-07-07 4:18 ` Damien Le Moal [this message]
2026-07-07 2:55 ` [PATCH V2 4/6] null_blk: move unregister_blkdev() after destroying dev in null_exit() Zizhi Wo
2026-07-07 4:19 ` Damien Le Moal
2026-07-07 2:55 ` [PATCH V2 5/6] null_blk: don't locklessly overwrite dev state after apply_fn Zizhi Wo
2026-07-07 3:38 ` Zizhi Wo
2026-07-07 4:21 ` Damien Le Moal
2026-07-07 7:33 ` Nilay Shroff
2026-07-07 8:24 ` Zizhi Wo
2026-07-07 2:55 ` [PATCH V2 6/6] null_blk: free global tag_set on init error path Zizhi Wo
2026-07-07 4:24 ` Damien Le Moal
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