netdev - Re: [PATCH] net: fix a concurrency bug in l2tp_tunnel

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Date:   Tue, 27 Apr 2021 17:50:35 +0100
From:   Tom Parkin <tparkin@...alix.com>
To:     "Gong, Sishuai" <sishuai@...due.edu>
Cc:     David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Matthias Schiffer <mschiffer@...verse-factory.net>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH] net: fix a concurrency bug in l2tp_tunnel_register()

On  Tue, Apr 27, 2021 at 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@...edance.com>
> Signed-off-by: Sishuai Gong <sishuai@...due.edu>
> Reported-by: Sishuai Gong <sishuai@...due.edu>
> ---

It came through this time.  Mysterious.

Anyway, thank you for reposting.  This looks good to me :-)

-- 
Tom Parkin
Katalix Systems Ltd
https://katalix.com
Catalysts for your Embedded Linux software development

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