linux-kernel - Re: CVE-2024-36966: erofs: reliably distinguish block based and fscache mode

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Date: Thu, 13 Jun 2024 22:02:41 +0800
From: Baokun Li <libaokun1@...wei.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC: Gao Xiang <hsiangkao@...ux.alibaba.com>, <cve@...nel.org>,
	<linux-kernel@...r.kernel.org>, <linux-cve-announce@...r.kernel.org>, Baokun
 Li <libaokun@...weicloud.com>, <yangerkun@...wei.com>
Subject: Re: CVE-2024-36966: erofs: reliably distinguish block based and
 fscache mode

On 2024/6/13 21:55, Greg Kroah-Hartman wrote:
> On Thu, Jun 13, 2024 at 07:21:14PM +0800, Baokun Li wrote:
>> On 2024/6/13 17:38, Gao Xiang wrote:
>>> Hi,
>>>
>>> (+Cc Baokun Li)
>>>
>>> On 2024/6/8 20:53, Greg Kroah-Hartman wrote:
>>>> Description
>>>> ===========
>>>>
>>>> In the Linux kernel, the following vulnerability has been resolved:
>>>>
>>>> erofs: reliably distinguish block based and fscache mode
>>>>
>>>> When erofs_kill_sb() is called in block dev based mode, s_bdev may not
>>>> have been initialised yet, and if CONFIG_EROFS_FS_ONDEMAND is enabled,
>>>> it will be mistaken for fscache mode, and then attempt to free an
>>>> anon_dev
>>>> that has never been allocated, triggering the following warning:
>>>>
>>>> ============================================
>>>> ida_free called for id=0 which is not allocated.
>>>> WARNING: CPU: 14 PID: 926 at lib/idr.c:525 ida_free+0x134/0x140
>>>> Modules linked in:
>>>> CPU: 14 PID: 926 Comm: mount Not tainted 6.9.0-rc3-dirty #630
>>>> RIP: 0010:ida_free+0x134/0x140
>>>> Call Trace:
>>>>    <TASK>
>>>>    erofs_kill_sb+0x81/0x90
>>>>    deactivate_locked_super+0x35/0x80
>>>>    get_tree_bdev+0x136/0x1e0
>>>>    vfs_get_tree+0x2c/0xf0
>>>>    do_new_mount+0x190/0x2f0
>>>>    [...]
>>>> ============================================
>>>>
>>>> Now when erofs_kill_sb() is called, erofs_sb_info must have been
>>>> initialised, so use sbi->fsid to distinguish between the two modes.
>>>>
>>>> The Linux kernel CVE team has assigned CVE-2024-36966 to this issue.
>>>>
>>>>
>>>> Affected and fixed versions
>>>> ===========================
>>>>
>>>>      Fixed in 6.6.32 with commit f9b877a7ee31
>>>>      Fixed in 6.8.11 with commit dcdd49701e42
>>>>      Fixed in 6.9 with commit 7af2ae1b1531
>>> For reference, this issue doesn't affect Linux kernel below 6.6.
>>>
>>> This behavior ("s_bdev may not be initialized in erofs_kill_sb()")
>>> is introduced due to commit aca740cecbe5 ("fs: open block device after
>>> superblock creation").
>>>
>>> In other words, previously .kill_sb() was called only after
>>> fill_super failed and problematic erofs_kill_sb() called due to
>>> setup_bdev_super() failure can only happen since Linux 6.6.
>>>
>>> Thanks,
>>> Gao Xiang
>> Exactly! I'm so sorry I forgot to add the Fixes tag.
> No worries.  I've updated the CVE database with this information and the
> json file and web site will show the new information soon when it gets
> propagated.
>
> thanks,
>
> greg k-h

Thank you very much for the update!

-- 
With Best Regards,
Baokun Li