Re: Question: consult patch

["zhangwensheng (E)" <zhangwensheng@huaweicloud.com>]

Hi Lee

I'm sorry I didn't fully understand you. did you mean the CVE
was caused by a commit which was applied to an internal kernel
version?  What commitment can be displayed? and I know that
mainline do not have the problem because of some code refactoring,
But are there any problems with some other stable branches?

thank you very much!
Wensheng

在 2022/8/12 15:26, Lee Jones 写道:
> On Fri, 12 Aug 2022, zhangwensheng (E) wrote:
>
>> Hi
>>
>> In CVE list last week, there is a new cve reported in asop 4.14 like below:
>> Reference link: https://lore.kernel.org/all/CAODzB9rgMexvLjE=WuTm+SN8SfUggaZgWG-aBcy6cotppju6mw@mail.gmail.com/T/
>>
>> ---
>> CVE-2022-20158: mm: backing-dev: Take a reference to the bdi in use to
>> prevent UAF
>>
>> CVSS v3 score is not assigned.
>>
>> AOSP kernel 4.14 contains following 2 patches.
>> - 69e8f03c5ced3e4e6fb4181f4dac185104e3420b ("mm: backing-dev: Take a
>> reference to the bdi in use to prevent UAF")
>> - 80d91b86a199798ee2321a0ab0f09e6e12764678 ("fs: explicitly unregister
>> per-superblock BDIs")
>>
>> The first commit 69e8f03("mm: backing-dev: Take a reference to the bdi
>> in use to prevent UAF") is not merged in the mainline and stable
>> kernels.
>> Commit 80d91b8 was merged in 5.16-rc1(commit hash is
>> 0b3ea0926afb8dde70cfab00316ae0a70b93a7cc) which requires commit
>> c6fd3ac ("mm: export bdi_unregister") that exports symbol of
>> bdi_unregister().
>>
>> Fixed status
>> mainline: [0b3ea0926afb8dde70cfab00316ae0a70b93a7cc]
>> ---
>>
>> As mentioned above, patch 69e8f03c5ced ("mm: backing-dev: Take a
>> reference to the bdi in use to prevent UAF") in asop 4.14 can fix
>> a null dereference problem, form my analysis, may like below:
>>
>> blk_cleanup_queue
>>      blk_put_queue
>>          kobject_put(&q->kobj)
>>                  blk_release_queue
>>                      blk_exit_queue
>>                          bdi_put
>>                              release_bdi  // bdi -> null
>> del_gendisk
>>      bdi_unregister(disk->queue->backing_dev_info) // null -> reference
>>
>>  From my analysis, In asop 4.14 kernel, in loop_remove function, there is
>> such a timing that executing "blk_cleanup_queue" first and then
>> "del_gendisk".
>> but because of the refcnt of queue will add by hte line
>> "WARN_ON_ONCE(!blk_get_queue(disk->queue));" in "device_add_disk", which may
>> not result in "bdi_put" releasing bdi  in "blk_cleanup_queue".
>>
>> I'm not sure where the problem is, so I want to ask Lee Jones who sent this
>> patch
>> for clarification.
>>
>> Thanks!
>>
>> Wensheng
>>
>> 在 2022/8/12 13:44, Christoph Hellwig 写道:
>>> On Fri, Aug 12, 2022 at 11:34:59AM +0800, zhangwensheng (E) wrote:
>>>> Hi Lee ：
>>>>       I saw your patch because of CVE-2022-20158, the patch like below:
>>>>
>>>> ---
>>>>       mm: backing-dev: Take a reference to the bdi in use to prevent UAF
>>> I can't see that patch anywhere, and I've not seen an bug report for it.
>>>
>>>>       Because of a distinct lack of locking and/or reference taking,
>>>>       blk_cleanup_queue() puts the final taken reference to the bdi, which
>>> .. and blk_cleanup_queue also is gone upstream.
>>>
>>> What am I missing?
> The issue reported in the aforementioned CVE was caused by a commit
> which was applied to an internal, device specific repository.  One
> that has never existed in Mainline.  I failed to reproduce the KASAN
> report in any upstream or stable tree without the offending patch
> applied.  The issue was fixed in all affected internal trees.
>