ksmbd: call rcu_barrier() in ksmbd_server_exit()

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>

diff --git a/fs/ksmbd/server.c b/fs/ksmbd/server.c
index 2ebf698..f9b2e0f 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();
 }