[PATCH 2/3] tun: Drain eBPF RCU callbacks on module exit

[Jiale Yao]

Replacing or clearing a TUN eBPF program defers its destruction to
tun_prog_free(). In the device teardown path, tun_free_netdev() can queue
this callback as a private destructor. The rcu_barrier() in
netdev_run_todo() runs before private destructors, so it cannot drain the
new callback.

After the last file or persistent-device reference is released, tun can
therefore unload before the callback runs. Drain outstanding callbacks at
the end of module cleanup so they cannot execute from freed module text.

Fixes: 96f84061620c ("tun: add eBPF based queue selection method")
Signed-off-by: Jiale Yao <yaojiale02@xxxxxxx>
---
 drivers/net/tun.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 5a302709a68a..bde5032bf4f4 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -3855,6 +3855,7 @@ static void __exit tun_cleanup(void)
 	misc_deregister(&tun_miscdev);
 	rtnl_link_unregister(&tun_link_ops);
 	unregister_netdevice_notifier(&tun_notifier_block);
+	rcu_barrier();
 }
 
 /* Get an underlying socket object from tun file.  Returns error unless file is
-- 
2.34.1