Messages in this thread | | | Date | Fri, 12 Aug 2022 15:38:55 +0800 | Subject | Re: Question: consult patch | From | "zhangwensheng (E)" <> |
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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. >
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