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

[Joseph Qi <joseph.qi@linux.alibaba.com>]

On 5/22/23 8:23 PM, Luís Henriques wrote:
> Joseph Qi <joseph.qi@linux.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