From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Miller <davem@davemloft.net>
Subject: Re: [PATCH net-next v2 01/16] l2tp: update sk_user_data while
 holding sk_callback_lock
Date: Mon, 12 Feb 2018 11:21:29 -0500 (EST)
Message-ID: <20180212.112129.1458610223636502379.davem@davemloft.net>
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From: James Chapman <jchapman@katalix.com>
Date: Mon, 12 Feb 2018 10:11:05 +0000

> Since L2TP hooks on sockets opened by userspace using sk_user_data, we
> may race with other socket families that attempt to use the same
> socket.
> 
> This problem was discovered by syzbot using AF_KCM. KCM has since been
> modified to use only TCP sockets to avoid hitting this issue but we
> should prevent such races in L2TP anyway.
> 
> Fixes: c8fffcea0a079 ("l2tp: Refactor l2tp core driver to make use of the common UDP tunnel function")
> Reported-by: syzbot+8865eaff7f9acd593945@syzkaller.appspotmail.com

Yikes.  Where is your signoff James?

> Kernel BUG at net/l2tp/l2tp_ppp.c:176!
> invalid opcode: 0000 [#1] SMP KASAN
> Dumping ftrace buffer:
>    (ftrace buffer empty)

And this oops dump should be before the various
fixes/reported-by/signed-off-by tags.

Thanks.