Re: [PATCH] net: fix a concurrency bug in l2tp_tunnel_register()

[Jakub Kicinski <kuba@kernel.org>]

On Tue, 27 Apr 2021 15:04:24 +0000 Gong, Sishuai wrote:
> l2tp_tunnel_register() registers a tunnel without fully
> initializing its attribute. This can allow another kernel thread
> running l2tp_xmit_core() to access the uninitialized data and
> then cause a kernel NULL pointer dereference error, as shown below.
> 
> Thread 1    Thread 2
> //l2tp_tunnel_register()
> list_add_rcu(&tunnel->list, &pn->l2tp_tunnel_list);
>            //pppol2tp_connect()
>            tunnel = l2tp_tunnel_get(sock_net(sk), info.tunnel_id);
>            // Fetch the new tunnel
>            ...
>            //l2tp_xmit_core()
>            struct sock *sk = tunnel->sock;
>            ...
>            bh_lock_sock(sk);
>            //Null pointer error happens
> tunnel->sock = sk;
> 
> Fix this bug by initializing tunnel->sock before adding the
> tunnel into l2tp_tunnel_list.
> 
> Reviewed-by: Cong Wang <cong.wang@bytedance.com>
> Signed-off-by: Sishuai Gong <sishuai@purdue.edu>
> Reported-by: Sishuai Gong <sishuai@purdue.edu>

Thanks for the patch! Unfortunately the patch in the email is
corrupted, looks like something removed spaces at the start of 
the lines which are expected in patches, e.g.:

»       pn·=·l2tp_pernet(net);$
$
+»      sk·=·sock->sk;$

Should have been:

 »      pn·=·l2tp_pernet(net);$
 $
+»      sk·=·sock->sk;$

Could you try to resend once more with git-send-email or via 
a different mail server?