CVE-2025-39860 — Bluetooth: Fix use-after-free in l2cap_sock_cleanup_listen()

Affected: Linux, Siemens RUGGEDCOM RST2428P, Siemens SCALANCE XC-300/XR-300/XC-400/XR-500WG/XR-500 family, Siemens SCALANCE XCH328, Siemens SCALANCE XCM324, Siemens SCALANCE XCM328, Siemens SCALANCE XCM332, Siemens SCALANCE XRH334 (24 V DC, 8xFO, CC), Siemens SCALANCE XRM334 (230 V AC, 12xFO), Siemens SCALANCE XRM334 (230 V AC, 8xFO) and 8 more

In the Linux kernel, the following vulnerability has been resolved:

Bluetooth: Fix use-after-free in l2cap_sock_cleanup_listen()

syzbot reported the splat below without a repro.

In the splat, a single thread calling bt_accept_dequeue() freed sk and touched it after that.

The root cause would be the racy l2cap_sock_cleanup_listen() call added by the cited commit.

bt_accept_dequeue() is called under lock_sock() except for l2cap_sock_release().

Two threads could see the same socket during the list iteration in bt_accept_dequeue():

CPU1 CPU2 (close()) ---- ---- sock_hold(sk) sock_hold(sk); lock_sock(sk) <-- block close() sock_put(sk) bt_accept_unlink(sk) sock_put(sk) <-- refcnt by bt_accept_enqueue() release_sock(sk) lock_sock(sk) sock_put(sk) bt_accept_unlink(sk) sock_put(sk) <-- last refcnt bt_accept_unlink(sk) <-- UAF

Depending on the timing, the other thread could show up in the "Freed by task" part.

Let's call l2cap_sock_cleanup_listen() under lock_sock() in l2cap_sock_release().

[0]: BUG: KASAN: slab-use-after-free in debug_spin_lock_before kernel/locking/spinlock_debug.c:86 [inline] BUG: KASAN: slab-use-after-free in do_raw_spin_lock+0x26f/0x2b0 kernel/locking/spinlock_debug.c:115 Read of size 4 at addr ffff88803b7eb1c4 by ta…

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CVE-2025-39860 — Bluetooth: Fix use-after-free in l2cap_sock_cleanup_listen()