ksmbd: fix use-after-free in session logoff

ksmbd: fix use-after-free in session logoff

commit 2fc9feff45d92a92cd5f96487655d5be23fb7e2b upstream.

The sess->user object can currently be in use by another thread, for
example if another connection has sent a session setup request to
bind to the session being free'd. The handler for that connection could
be in the smb2_sess_setup function which makes use of sess->user.

Signed-off-by: Sean Heelan <seanheelan@gmail.com>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Nazar Kalashnikov <sivartiwe@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>