linux-kernel - Re: [PATCH] ocfs2: fix use-after-free when unmounting read-only filesystem

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Message-ID: <846d9e88-2b66-1941-a791-6b3e286bdb66@linux.alibaba.com>
Date:   Tue, 23 May 2023 10:41:33 +0800
From:   Joseph Qi <joseph.qi@...ux.alibaba.com>
To:     Luís Henriques <lhenriques@...e.de>
Cc:     ocfs2-devel@....oracle.com, linux-kernel@...r.kernel.org,
        Mark Fasheh <mark@...heh.com>,
        Joel Becker <jlbec@...lplan.org>,
        Heming Zhao <heming.zhao@...e.com>
Subject: Re: [PATCH] ocfs2: fix use-after-free when unmounting read-only
 filesystem



On 5/22/23 8:23 PM, Luís Henriques wrote:
> Joseph Qi <joseph.qi@...ux.alibaba.com> writes:
> 
>> On 5/22/23 6:25 PM, Luís Henriques wrote:
>>> It's trivial to trigger a use-after-free bug in the ocfs2 quotas code using
>>> fstest generic/452.  After mounting a filesystem as read-only, quotas are
>>
>> generic/452 is for testing ext4 mounted with dax and ro.
>> But ocfs2 doesn't support dax yet.
> 
> Right, but I think it's still useful to run the 'generic' test-suite in a
> filesystem.  We can always find issues in the test itself or, in this
> case, a bug in the filesystem.
> 
>>> suspended and ocfs2_mem_dqinfo is freed through ->ocfs2_local_free_info().  When
>>> unmounting the filesystem, an UAF access to the oinfo will eventually cause a
>>> crash.
>>
>> In ocfs2_fill_super(), it won't enable quota if is a readonly mount.
>> Do you mean remount as readonly?
> 
> Yes, sorry. Instead of "mounting", the patch changelog should say
> 
>   "After remounting a filesystem as read-only..."
> 
> Cheers,

Okay, look into the code flow, it does have problem when remount with
read-only.
BTW, it seems that we can't call into quota_disable() again, which will
call free_file_info().

Thanks,
Joseph