Bluetooth: Fix refcount use-after-free issue
There is no lock preventing both l2cap_sock_release() and
chan->ops->close() from running at the same time.
If we consider Thread A running l2cap_chan_timeout() and Thread B running
l2cap_sock_release(), expected behavior is:
A::l2cap_chan_timeout()->l2cap_chan_close()->l2cap_sock_teardown_cb()
A::l2cap_chan_timeout()->l2cap_sock_close_cb()->l2cap_sock_kill()
B::l2cap_sock_release()->sock_orphan()
B::l2cap_sock_release()->l2cap_sock_kill()
where,
sock_orphan() clears "sk->sk_socket" and l2cap_sock_teardown_cb() marks
socket as SOCK_ZAPPED.
In l2cap_sock_kill(), there is an "if-statement" that checks if both
sock_orphan() and sock_teardown() has been run i.e. sk->sk_socket is NULL
and socket is marked as SOCK_ZAPPED. Socket is killed if the condition is
satisfied.
In the race condition, following occurs:
A::l2cap_chan_timeout()->l2cap_chan_close()->l2cap_sock_teardown_cb()
B::l2cap_sock_release()->sock_orphan()
B::l2cap_sock_release()->l2cap_sock_kill()
A::l2cap_chan_timeout()->l2cap_sock_close_cb()->l2cap_sock_kill()
In this scenario, "if-statement" is true in both B::l2cap_sock_kill() and
A::l2cap_sock_kill() and we hit "refcount: underflow; use-after-free" bug.
Similar condition occurs at other places where teardown/sock_kill is
happening:
l2cap_disconnect_rsp()->l2cap_chan_del()->l2cap_sock_teardown_cb()
l2cap_disconnect_rsp()->l2cap_sock_close_cb()->l2cap_sock_kill()
l2cap_conn_del()->l2cap_chan_del()->l2cap_sock_teardown_cb()
l2cap_conn_del()->l2cap_sock_close_cb()->l2cap_sock_kill()
l2cap_disconnect_req()->l2cap_chan_del()->l2cap_sock_teardown_cb()
l2cap_disconnect_req()->l2cap_sock_close_cb()->l2cap_sock_kill()
l2cap_sock_cleanup_listen()->l2cap_chan_close()->l2cap_sock_teardown_cb()
l2cap_sock_cleanup_listen()->l2cap_sock_kill()
Protect teardown/sock_kill and orphan/sock_kill by adding hold_lock on
l2cap channel to ensure that the socket is killed only after marked as
zapped and orphan.
Signed-off-by: Manish Mandlik <mmandlik@google.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
2 files changed
