ksmbd: fix slab-use-after-free in ksmbd_smb2_session_create

There is a race condition between ksmbd_smb2_session_create and
ksmbd_expire_session. This patch add missing sessions_table_lock
while adding/deleting session from global session table.

Cc: [email protected] # v5.15+
Reported-by: Norbert Szetei <[email protected]>
Signed-off-by: Namjae Jeon <[email protected]>

mgmt/user_session.c

@@ -175,6 +175,7 @@ static void ksmbd_expire_session(struct ksmbd_conn *conn)
 	unsigned long id;
 	struct ksmbd_session *sess;
 
+	down_write(&sessions_table_lock);
 	down_write(&conn->session_lock);
 	xa_for_each(&conn->sessions, id, sess) {
 		if (atomic_read(&sess->refcnt) == 0 &&
@@ -193,6 +194,7 @@ static void ksmbd_expire_session(struct ksmbd_conn *conn)
 		}
 	}
 	up_write(&conn->session_lock);
+	up_write(&sessions_table_lock);
 }
 
 int ksmbd_session_register(struct ksmbd_conn *conn,
@@ -239,7 +241,6 @@ void ksmbd_sessions_deregister(struct ksmbd_conn *conn)
 			}
 		}
 	}
-	up_write(&sessions_table_lock);
 
 	down_write(&conn->session_lock);
 	xa_for_each(&conn->sessions, id, sess) {
@@ -264,6 +265,7 @@ void ksmbd_sessions_deregister(struct ksmbd_conn *conn)
 		}
 	}
 	up_write(&conn->session_lock);
+	up_write(&sessions_table_lock);
 }
 
 struct ksmbd_session *ksmbd_session_lookup(struct ksmbd_conn *conn,