netdev - Re: [PATCH v3] net: fix a concurrency bug in l2tp_tunnel

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Message-ID: <CAM_iQpUV-rmGdn1g7jn==53wLQ0MvM_bx4cJBo4AEDVZXPehRQ@mail.gmail.com>
Date:   Fri, 23 Apr 2021 10:38:45 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Sishuai Gong <sishuai@...due.edu>
Cc:     David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, tparkin@...alix.com,
        Matthias Schiffer <mschiffer@...verse-factory.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH v3] net: fix a concurrency bug in l2tp_tunnel_register()

On Wed, Apr 21, 2021 at 12:25 PM Sishuai Gong <sishuai@...due.edu> 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.
>
> Signed-off-by: Sishuai Gong <sishuai@...due.edu>
> Reported-by: Sishuai Gong <sishuai@...due.edu>

Reviewed-by: Cong Wang <cong.wang@...edance.com>

Thanks.