Note: Versions mentioned in the description apply only to the upstream kernel-debug-modules package and not the kernel-debug-modules package as distributed by Centos. See How to fix? for Centos:8 relevant fixed versions and status.

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

tipc: wait and exit until all work queues are done

On some host, a crash could be triggered simply by repeating these commands several times:

modprobe tipc

tipc bearer enable media udp name UDP1 localip 127.0.0.1

rmmod tipc

[] BUG: unable to handle kernel paging request at ffffffffc096bb00 [] Workqueue: events 0xffffffffc096bb00 [] Call Trace: [] ? process_one_work+0x1a7/0x360 [] ? worker_thread+0x30/0x390 [] ? create_worker+0x1a0/0x1a0 [] ? kthread+0x116/0x130 [] ? kthread_flush_work_fn+0x10/0x10 [] ? ret_from_fork+0x35/0x40

When removing the TIPC module, the UDP tunnel sock will be delayed to release in a work queue as sock_release() can't be done in rtnl_lock(). If the work queue is schedule to run after the TIPC module is removed, kernel will crash as the work queue function cleanup_beareri() code no longer exists when trying to invoke it.

To fix it, this patch introduce a member wq_count in tipc_net to track the numbers of work queues in schedule, and wait and exit until all work queues are done in tipc_exit_net().

• https://access.redhat.com/security/cve/CVE-2021-47163
• https://git.kernel.org/stable/c/04c26faa51d1e2fe71cf13c45791f5174c37f986
• https://git.kernel.org/stable/c/5195ec5e365a2a9331bfeb585b613a6e94f98dba
• https://git.kernel.org/stable/c/b9f5b7ad4ac3af006443f535b1ce7bff1d130d7d
• https://git.kernel.org/stable/c/d1f76dfadaf8f47ed1753f97dbcbd41c16215ffa