Re: [PATCH net-next v2 01/16] l2tp: update sk_user_data while holding sk_callback_lock

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.