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@xxxxxxxxxxxxxx/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. -- DEPRECATED: Please use lee@xxxxxxxxxx
