CVE-2021-47163 is a vulnerability identified in the Linux kernel's Transparent Inter-Process Communication (TIPC) module. The flaw arises from improper handling of work queues during the removal of the TIPC kernel module. Specifically, when the TIPC module is removed (rmmod tipc), the UDP tunnel socket associated with it is delayed in release because sock_release() cannot be executed while holding the rtnl_lock(). This delay causes the work queue function cleanup_beareri() to be scheduled after the module has been unloaded, leading to a kernel crash due to a use-after-free or invalid function pointer dereference. The crash is triggered by repeated execution of commands that load the TIPC module, enable the UDP bearer, and then remove the module. The root cause is that the work queue function code no longer exists when the work queue attempts to run, causing a kernel paging fault. The fix introduced involves adding a wq_count member to tipc_net to track the number of scheduled work queues and ensuring that the module exit function (tipc_exit_net()) waits until all work queues have completed before allowing the module to be fully removed. This prevents the kernel from invoking non-existent code and crashing. No known exploits are reported in the wild, and the vulnerability affects Linux kernel versions prior to the patch. The vulnerability is a denial-of-service (DoS) type, causing kernel crashes and potential system instability.

For European organizations, the primary impact of CVE-2021-47163 is the risk of denial-of-service conditions on Linux systems utilizing the TIPC module, particularly those that employ UDP bearers for inter-process or inter-node communication. Systems affected may experience kernel panics and crashes, leading to service interruptions, potential data loss, and operational downtime. This can be critical for infrastructure providers, telecom operators, and enterprises relying on Linux-based servers for critical applications. Although no remote code execution or privilege escalation is indicated, repeated exploitation could disrupt services and impact availability. Organizations running containerized environments or cloud platforms with Linux kernels that include TIPC support may also be vulnerable. Given the kernel-level nature of the crash, recovery typically requires a system reboot, which could affect high-availability environments. The absence of known exploits reduces immediate risk, but the vulnerability should be addressed promptly to prevent potential exploitation or accidental triggering in production environments.

1. Apply the latest Linux kernel patches that address CVE-2021-47163 as soon as they become available from your Linux distribution vendor. This is the definitive fix preventing the kernel crash. 2. If patching is not immediately possible, consider disabling the TIPC module (modprobe -r tipc) and avoid loading it unless absolutely necessary. 3. Review and audit any scripts or automation that load and unload the TIPC module or configure UDP bearers to ensure they do not repeatedly trigger the vulnerable sequence. 4. Implement kernel crash monitoring and alerting to detect any unexpected panics related to TIPC module usage. 5. For critical systems, schedule maintenance windows to apply patches and reboot systems to clear any unstable states caused by this vulnerability. 6. Engage with Linux distribution security advisories and subscribe to relevant mailing lists to stay informed about updates and backported fixes. 7. For environments using custom or embedded Linux kernels, coordinate with vendors or maintainers to integrate the patch promptly. 8. Consider isolating or limiting access to systems that require TIPC functionality to reduce exposure.