CVE-2026-74587sctp: fix use-after-free of cached ASCONF chunk

Official description

In the Linux kernel, the following vulnerability has been resolved: sctp: fix use-after-free of cached ASCONF chunk addip_last_asconf caches the outstanding outbound ASCONF chunk. The normal ASCONF-ACK completion path releases the chunk and clears the pointer. However, sctp_asconf_queue_teardown() releases the cached chunk without clearing addip_last_asconf. During peer restart handling, sctp_sf_do_dupcook_a() queues SCTP_CMD_PURGE_ASCONF_QUEUE, which invokes sctp_asconf_queue_teardown() while the association remains alive and leaves the pointer dangling. A delayed authenticated ASCONF-ACK can then reach sctp_sf_do_asconf_ack(), which accesses the stale chunk and passes it to sctp_process_asconf_ack(), causing a use-after-free and a second release. Clearing the pointer exposes a race with T4 expiry. Peer restart handling queues the timer stop before the purge, but SCTP_CMD_TIMER_STOP uses timer_delete(), which does not wait for a callback already running on another CPU. Such a callback can reach sctp_sf_t4_timer_expire() after the purge and dereference NULL. Clear addip_last_asconf after releasing the cached chunk, and make sctp_sf_t4_timer_expire() consume a stale T4 expiry if no outstanding ASCONF remains.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/10459b03e2d9ee12435e96f587de4d4cacdbf435
• https://git.kernel.org/stable/c/e1bb114e09372fd6e03387ced9ef566da336ed6c
• https://git.kernel.org/stable/c/179676f0166230c80053a392303485b37c93dd33
• https://git.kernel.org/stable/c/dc67d528c2fa939cec7fe3bf7f3089c8d281ca3d
• https://git.kernel.org/stable/c/618b5c6d049896fcfabb91afc072954c92cb2693
• https://git.kernel.org/stable/c/07daf4f9750104960a1d60831b2353c0d41f35fb
• https://git.kernel.org/stable/c/d949992bc3f00027a2c755e860a11950c75f6073
• https://git.kernel.org/stable/c/8c283e7b56adce00193837f3311b06662466fb21