In the Linux kernel, the following vulnerability has been resolved:
Bluetooth: L2CAP: use chan timer to close channels in cleanup_listen()
l2cap_chan_close() removes the channel from conn->chan_l, which must be done under conn->lock. cleanup_listen() runs under the parent sk_lock, so acquiring conn->lock would invert the established conn->lock -> chan->lock -> sk_lock order.
Instead of calling l2cap_chan_close() directly, schedule l2cap_chan_timeout with delay 0 to close the channel asynchronously. The timeout handler already acquires conn->lock and chan->lock in the correct order.
The timer is only armed when chan->conn is still set: if it is already NULL, l2cap_conn_del() has already processed this channel (l2cap_chan_del + l2cap_sock_teardown_cb + l2cap_sock_close_cb), so there is nothing left to do. If l2cap_conn_del() races in after the timer is armed, __clear_chan_timer() inside l2cap_chan_del() cancels it; if the timer has already fired, the handler returns harmlessly because chan->conn was cleared.
References
- https://git.kernel.org/stable/c/3634cbdc2eb414b69ffa752ddbe5e0458518e321
- https://git.kernel.org/stable/c/50dfec218808b148ab4247b1858031b7a32015c5
- https://git.kernel.org/stable/c/7555fd885a0603f50e49a655850a1f2bd8a25398
- https://git.kernel.org/stable/c/859d3ace791ed878ae9ba5522c7844d960da8f88
- https://git.kernel.org/stable/c/89dec92041717b027216e110599e4f6d6c921b79
- https://git.kernel.org/stable/c/8c8e620467a7b51562dbcefbd1f09f288d7d710d
- https://git.kernel.org/stable/c/deb8493a8fa599f6c95e2465b12bfdfb7f94a1d9
- https://git.kernel.org/stable/c/e1c100e2d61bd8c718b7d91fe3e050780a9bf72d