5.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Yu Kuai yukuai3@huawei.com
[ Upstream commit 844b8cdc681612ff24df62cdefddeab5772fadf1 ]
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.
Fixes: b7aa3d39385d ("nbd: add a reconfigure netlink command") Reported-by: syzbot+6b0df248918b92c33e6a@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/675bfb65.050a0220.1a2d0d.0006.GAE@google.com/ Signed-off-by: Yu Kuai yukuai3@huawei.com Reviewed-by: Christoph Hellwig hch@lst.de Link: https://lore.kernel.org/r/20250103092859.3574648-1-yukuai1@huaweicloud.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/block/nbd.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c index f2d847ffcbc75..a3a0f09a4f47d 100644 --- a/drivers/block/nbd.c +++ b/drivers/block/nbd.c @@ -2039,6 +2039,7 @@ static void nbd_disconnect_and_put(struct nbd_device *nbd) flush_workqueue(nbd->recv_workq); nbd_clear_que(nbd); nbd->task_setup = NULL; + clear_bit(NBD_RT_BOUND, &nbd->config->runtime_flags); mutex_unlock(&nbd->config_lock);
if (test_and_clear_bit(NBD_RT_HAS_CONFIG_REF,