In the Linux kernel, the following vulnerability has been resolved:
ksmbd: fix use-after-free in SMB request handling
A race condition exists between SMB request handling in
ksmbd_conn_handler_loop() and the freeing of ksmbd_conn in the
workqueue handler handle_ksmbd_work(). This leads to a UAF.
- KASAN: slab-use-after-free Read in handle_ksmbd_work
- KASAN: slab-use-after-free in rtlock_slowlock_locked
This race condition arises as follows:
ksmbd_conn_handler_loop()waits forconn->r_countto reach zero:
wait_event(conn->r_count_q, atomic_read(&conn->r_count) == 0);
- Meanwhile,
handle_ksmbd_work()decrementsconn->r_countusing
atomic_dec_return(&conn->r_count), and if it reaches zero, calls
ksmbd_conn_free(), which frees conn.
- However, after
handle_ksmbd_work()decrementsconn->r_count,
conn->r_count_q in the following line:
waitqueue_active(&conn->r_count_q) or wake_up(&conn->r_count_q)
This results in a UAF, as conn has already been freed.The discovery of this UAF can be referenced in the following PR for syzkaller's support for SMB requests.