CVE-2025-21823 is a medium severity vulnerability in the Linux kernel's batman-adv module related to the handling of the ELP metric worker. The issue arises from the previous design where per-interface neighbor metric workers could continue running even after interfaces were removed or the module unloaded, potentially causing invalid memory accesses. The fix involves removing the per-interface neighbor metric worker and consolidating metric gathering within the interface worker, using RCU locking mechanisms carefully to avoid deadlocks and ensure proper cleanup.