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

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Message-ID: <20210428152319.163ef732@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Wed, 28 Apr 2021 15:23:23 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     "Gong, Sishuai" <sishuai@...due.edu>
Cc:     David Miller <davem@...emloft.net>,
        "tparkin@...alix.com" <tparkin@...alix.com>,
        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 Wed, 28 Apr 2021 12:45:34 -0700 Jakub Kicinski wrote:
> 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@...edance.com>
> > Signed-off-by: Sishuai Gong <sishuai@...due.edu>
> > Reported-by: Sishuai Gong <sishuai@...due.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?

Ignore me, this patch has already been merged.