Vulnerability CVE-2022-48931
Published: 2024-08-22

Description:
In the Linux kernel, the following vulnerability has been resolved:

configfs: fix a race in configfs_{,un}register_subsystem()

When configfs_register_subsystem() or configfs_unregister_subsystem()
is executing link_group() or unlink_group(),
it is possible that two processes add or delete list concurrently.
Some unfortunate interleavings of them can cause kernel panic.

One of cases is:
A --> B --> C --> D
A <-- B <-- C <-- D

delete list_head *B | delete list_head *C
--------------------------------|-----------------------------------
configfs_unregister_subsystem | configfs_unregister_subsystem
unlink_group | unlink_group
unlink_obj | unlink_obj
list_del_init | list_del_init
__list_del_entry | __list_del_entry
__list_del | __list_del
// next == C |
next->prev = prev |
| next->prev = prev
prev->next = next |
| // prev == B
| prev->next = next

Fix this by adding mutex when calling link_group() or unlink_group(),
but parent configfs_subsystem is NULL when config_item is root.
So I create a mutex configfs_subsystem_mutex.

 References:
https://git.kernel.org/stable/c/40805099af11f68c5ca7dbcfacf455da8f99f622
https://git.kernel.org/stable/c/d1654de19d42f513b6cfe955cc77e7f427e05a77
https://git.kernel.org/stable/c/a37024f7757c25550accdebf49e497ad6ae239fe
https://git.kernel.org/stable/c/b7e2b91fcb5c78c414e33dc8d50642e307ca0c5a
https://git.kernel.org/stable/c/a7ab53d3c27dfe83bb594456b9f38a37796ec39b
https://git.kernel.org/stable/c/e7a66dd2687758718eddd79b542a95cf3aa488cc
https://git.kernel.org/stable/c/3aadfd46858b1f64d4d6a0654b863e21aabff975
https://git.kernel.org/stable/c/84ec758fb2daa236026506868c8796b0500c047d
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