ksmbd: call rcu_barrier() in ksmbd_server_exit()

commit eb307d09fe15844fdaebeb8cc8c9b9e925430aa5 upstream.

racy issue is triggered the bug by racing between closing a connection
and rmmod. In ksmbd, rcu_barrier() is not called at module unload time,
so nothing prevents ksmbd from getting unloaded while it still has RCU
callbacks pending. It leads to trigger unintended execution of kernel
code locally and use to defeat protections such as Kernel Lockdown

Cc: stable@vger.kernel.org
Reported-by: zdi-disclosures@trendmicro.com # ZDI-CAN-20477
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/ksmbd/server.c b/fs/ksmbd/server.c
index 0d8242789dc8fd7a4e39d0ca52bd6e0263275dca..cd8a873347a7990fba67e16c9390a5173fd91a00 100644 (file)
--- a/fs/ksmbd/server.c
+++ b/fs/ksmbd/server.c
@@ -606,6 +606,7 @@ err_unregister:
 static void __exit ksmbd_server_exit(void)
 {
        ksmbd_server_shutdown();
+       rcu_barrier();
        ksmbd_release_inode_hash();
 }