High [CVE-2026-80521] Unlink scc_entry in unix_del_edge

In the Linux kernel, the following vulnerability has been resolved: af_unix: Unlink scc_entry in unix_del_edge(). Kyle Zeng reported that GC could free a dead SCC partially.

The scenario is as follows: 1) Create two SCCs: X -. A B ^--' 2) Run the following concurrently: 2-1) send() sk-B to sk-B from sk-X 2-2) close() both A and B At 2-1), there is a small window where unix_add_edges() publishes a new edge (B B) to GC but its skb is not queued by skb_queue_tail().

If 2-2) completes before skb_queue_tail() and GC is triggered, it judges A B as dead, but B is not freed because GC cannot collect the not-yet-queued skb holding the B B edge. X -.

A B -. This edge is visible ^--' ^..' but skb is not This itself is not a problem since the next GC run will judge B as dead as well and free it finally.

A B -. ^--' ^--' However, X's SCC forces the next GC to call unix_walk_scc_fast(), and it iterates over A through B's scc_entry. Let's unlink scc_entry before freeing the vertex in unix_del_edge().

A race condition during concurrent `send()` and `close()` operations can lead to the garbage collector (GC) partially freeing a Strongly Connected Component (SCC). This inconsistent state may cause subsequent GC operations to iterate over a partially freed entry, potentially leading to system instability or a denial of service.