nbd: don't allow reconnect after disconnect

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: nbd: don't allow reconnect after disconnect Following process can cause nbd_config UAF: 1) grab nbd_config temporarily; 2) nbd_genl_disconnect() flush all recv_work() and release the initial reference: nbd_genl_disconnect nbd_disconnect_and_put nbd_disconnect flush_workqueue(nbd->recv_workq) if (test_and_clear_bit(NBD_RT_HAS_CONFIG_REF, ...)) nbd_config_put -> due to step 1), reference is still not zero 3) nbd_genl_reconfigure() queue recv_work() again; nbd_genl_reconfigure config = nbd_get_config_unlocked(nbd) if (!config) -> succeed if (!test_bit(NBD_RT_BOUND, ...)) -> succeed nbd_reconnect_socket queue_work(nbd->recv_workq, &args->work) 4) step 1) release the reference; 5) Finially, recv_work() will trigger UAF: recv_work nbd_config_put(nbd) -> nbd_config is freed atomic_dec(&config->recv_threads) -> UAF Fix the problem by clearing NBD_RT_BOUND in nbd_genl_disconnect(), so that nbd_genl_reconfigure() will fail.

References

• https://git.kernel.org/stable/c/e70a578487a47d7cf058904141e586684d1c3381
• https://git.kernel.org/stable/c/6bef6222a3f6c7adb6396f77f25a3579d821b09a
• https://git.kernel.org/stable/c/e3be8862d73cac833e0fb7602636c19c6cb94b11
• https://git.kernel.org/stable/c/e7343fa33751cb07c1c56b666bf37cfca357130e
• https://git.kernel.org/stable/c/d208d2c52b652913b5eefc8ca434b0d6b757f68f
• https://git.kernel.org/stable/c/a8ee6ecde2b7bfb58c8a3afe8a9d2b848f580739
• https://git.kernel.org/stable/c/9793bd5ae4bdbdb2dde401a3cab94a6bfd05e302
• https://git.kernel.org/stable/c/844b8cdc681612ff24df62cdefddeab5772fadf1