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 GC run will judge B as dead as well and free it finally. X -. A B -. ^--' ^--' However, X's SCC forces the 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().
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Introduced by 4090fa3 , fixed by 594d905
Severity score breakdown
CVSS version: CVSS v3.0
Base score 7.8 · High
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
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