In the Linux kernel, the following vulnerability has been resolved:
Bluetooth: fix UAF in l2cap_sock_cleanup_listen() vs l2cap_conn_del()
bt_accept_dequeue() unlinks a not-yet-accepted child from the parent accept queue and release_sock()s it before returning, so the returned sk has no caller reference and is unlocked.
l2cap_sock_cleanup_listen() walks these children on listening-socket close. A concurrent HCI disconnect drives hci_rx_work -> l2cap_conn_del() which runs l2cap_chan_del() + l2cap_sock_kill() and frees the child sk and its l2cap_chan; cleanup_listen() then uses both:
BUG: KASAN: slab-use-after-free in l2cap_sock_kill l2cap_sock_kill / l2cap_sock_cleanup_listen / __x64_sys_close Freed by: l2cap_conn_del -> l2cap_sock_close_cb -> l2cap_sock_kill
This is distinct from the two fixes already in this area: commit e83f5e24da741 (Bluetooth: serialize accept_q access) serialises the accept_q list/poll and takes temporary refs inside bt_accept_dequeue(), and CVE-2025-39860 serialises the userspace close()/accept() race by calling cleanup_listen() under lock_sock() in l2cap_sock_release(). Neither covers l2cap_conn_del() running from hci_rx_work, so this UAF still reproduces on current bluetooth/master.
Take the reference at the source: bt_accept_dequeue() does sock_hold() while sk is still locked, before release_sock(); callers sock_put(). cleanup_listen() pins the chan with l2cap_chan_hold_unless_zero() under a brief child sk lock (serialising vs l2cap_sock_teardown_cb()), drops it before l2cap_chan_lock(), and skips a duplicate l2cap_sock_kill() on SOCK_DEAD. conn->lock is not taken here: cleanup_listen() runs under the parent sk lock and that would invert conn->lock -> chan->lock -> sk_lock (lockdep).
KASAN/SMP: an unprivileged listen/close vs HCI-disconnect race produced 12 use-after-free reports per run before this change; 0, and no lockdep report, over 1600+ raced iterations after it on bluetooth/master.
References
- https://git.kernel.org/stable/c/407217734835d21d4e0105ebf347860dc1806f88
- https://git.kernel.org/stable/c/5d86d2f1b4d9a508c441d3e45277ae1a73cfed57
- https://git.kernel.org/stable/c/751de6ec671fe75ad9cf65a0638d2a06b6a5984d
- https://git.kernel.org/stable/c/7eebd4c2c86f573af87ff165d08a83432eb0b919
- https://git.kernel.org/stable/c/87c543e2f78d0871f271df92dab98901bbd5b6f5
- https://git.kernel.org/stable/c/a5ca86a6097a8b030ca3226cd300b17ed330f966
- https://git.kernel.org/stable/c/ab1513597c6cf17cd1ad2a21e3b045421b48e022
- https://git.kernel.org/stable/c/added1213395071470a900cc845a042fb51882a6