Re: Question: consult patch

[Lee Jones <lee.jones@linaro.org>]

> thank you very much!

Please refrain from top-posting.

> 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.
> 
> 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?

Yes, CVE-2022-20158 pertains to an issue on an internal repo.

Mainline and Stable were unaffected.

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