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?
.
