Race condition

In the Linux kernel, the following vulnerability has been resolved:

ksmbd: fix race condition between session lookup and expire

Thread A + Thread B
ksmbd_session_lookup | smb2_sess_setup
sess = xa_load |
|
| xa_erase(&conn->sessions, sess->id);
|
| ksmbd_session_destroy(sess) –> kfree(sess)
|
// UAF! |
sess->last_active = jiffies |
+

This patch add rwsem to fix race condition between ksmbd_session_lookup
and ksmbd_expire_session.