CVE-2025-68319

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

netconsole: Acquire su_mutex before navigating configs hierarchy

There is a race between operations that iterate over the userdata

cg_children list and concurrent add/remove of userdata items through

configfs. The update_userdata() function iterates over the

nt->userdata_group.cg_children list, and count_extradata_entries() also

iterates over this same list to count nodes.

Quoting from Documentation/filesystems/configfs.rst:

> A subsystem can navigate the cg_children list and the ci_parent pointer

> to see the tree created by the subsystem. This can race with configfs'

> management of the hierarchy, so configfs uses the subsystem mutex to

> protect modifications. Whenever a subsystem wants to navigate the

> hierarchy, it must do so under the protection of the subsystem

> mutex.

Without proper locking, if a userdata item is added or removed

concurrently while these functions are iterating, the list can be

accessed in an inconsistent state. For example, the list_for_each() loop

can reach a node that is being removed from the list by list_del_init()

which sets the nodes' .next pointer to point to itself, so the loop will

never end (or reach the WARN_ON_ONCE in update_userdata() ).

Fix this by holding the configfs subsystem mutex (su_mutex) during all

operations that iterate over cg_children.

This includes:

- userdatum_value_store() which calls update_userdata() to iterate over

cg_children

- All sysdata_*_enabled_store() functions which call

count_extradata_entries() to iterate over cg_children

The su_mutex must be acquired before dynamic_netconsole_mutex to avoid

potential lock ordering issues, as configfs operations may already hold

su_mutex when calling into our code.