CVE-2021-47163: 
Linux Kernel vulnerability analysis and mitigation

A vulnerability in the Linux kernel's TIPC (Transparent Inter-Process Communication) module has been identified as CVE-2021-47163. The issue occurs when removing the TIPC module while UDP tunnel sockets are still being processed. The vulnerability was discovered when a crash could be triggered by repeatedly loading and unloading the TIPC module with UDP bearer enabled (Kernel Git).

The vulnerability stems from a race condition in the TIPC module's cleanup process. When removing the TIPC module, the UDP tunnel socket is scheduled for delayed release in a work queue since sock_release() cannot be executed while holding the rtnl_lock(). If the work queue executes after the TIPC module is removed, the kernel crashes because the cleanup_beareri() function no longer exists when the system attempts to invoke it (Kernel Git).

When successfully exploited, this vulnerability results in a kernel crash, leading to a denial of service condition. The issue can be triggered by executing a specific sequence of commands involving the loading and unloading of the TIPC module with UDP bearer configuration (Kernel Git).

The vulnerability can be triggered by executing the following sequence of commands: 'modprobe tipc', 'tipc bearer enable media udp name UDP1 localip 127.0.0.1', and 'rmmod tipc'. The issue is reproducible on affected systems when these commands are repeated several times (Kernel Git).

The issue has been fixed by introducing a wq_count member in tipc_net to track the number of work queues scheduled. The fix ensures that the system waits for all work queues to complete before allowing the TIPC module to exit, preventing the race condition (Kernel Git).