From: Yu Kuai <yukuai3@xxxxxxxxxx>
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@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://lore.kernel.org/all/675bfb65.050a0220.1a2d0d.0006.GAE@xxxxxxxxxx/
Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
---
drivers/block/nbd.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index b1a5af69a66d..259bd57fc529 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -2179,6 +2179,7 @@ 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,
--
2.39.2
