BUG: unable to handle kernel NULL pointer dereference at 0000000000000080
IP: [<ffffffff8359d10c>] l2tp_session_free+0x11c/0x200 net/l2tp/l2tp_core.c:1671
PGD 1d9012067 PUD 1d2c67067 PMD 0 
Oops: 0002 [#1] PREEMPT SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 0 PID: 4 Comm: kworker/0:0 Not tainted 4.4.140-g789274d #67
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: sock_diag_events sock_diag_broadcast_destroy_work
task: ffff8801d99ac800 task.stack: ffff8801d99f0000
RIP: 0010:[<ffffffff8359d10c>]  [<ffffffff8359d10c>] l2tp_session_free+0x11c/0x200 net/l2tp/l2tp_core.c:1671
RSP: 0018:ffff8801d99f7b28  EFLAGS: 00010246
RAX: dffffc0000000000 RBX: ffff8800a71fcc80 RCX: 0000000000000000
RDX: 1ffff10016515a10 RSI: ffffffff8359d0e1 RDI: ffff8800b28ad080
RBP: ffff8801d99f7b48 R08: ffff8801d99ad128 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff8800b28acf00
R13: ffff8800a71fcc88 R14: 0000000000000000 R15: ffff8800b28acf58
FS:  0000000000000000(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000080 CR3: 00000001da25b000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffff8800a71fcd28 dffffc0000000000 ffff8800a71fcc80 ffffffff835a6bc0
 ffff8801d99f7ba0 ffffffff8359f519 ffff8800b28acfd8 ffffed00165159eb
 ffff8800b28acf58 ffff8800b28acf20 ffff8800b28acf00 ffff8800adc9abc0
Call Trace:
 [<ffffffff8359f519>] l2tp_session_dec_refcount_1 net/l2tp/l2tp_core.h:293 [inline]
 [<ffffffff8359f519>] l2tp_tunnel_closeall+0x2b9/0x350 net/l2tp/l2tp_core.c:1279
 [<ffffffff8359fd02>] l2tp_tunnel_destruct+0x2f2/0x590 net/l2tp/l2tp_core.c:1230
 [<ffffffff82f2ef9c>] sk_destruct+0x4c/0x4c0 net/core/sock.c:1447
 [<ffffffff82fcc15a>] sock_diag_broadcast_destroy_work+0x21a/0x390 net/core/sock_diag.c:153
 [<ffffffff81181f8f>] process_one_work+0x7df/0x1600 kernel/workqueue.c:2064
 [<ffffffff81182e89>] worker_thread+0xd9/0xfc0 kernel/workqueue.c:2196
 [<ffffffff81190998>] kthread+0x268/0x300 kernel/kthread.c:211
 [<ffffffff838c2bd5>] ret_from_fork+0x55/0x80 arch/x86/entry/entry_64.S:510
Code: 49 8d bc 24 80 01 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 d0 00 00 00 4d 8b b4 24 80 01 00 00 <f0> 41 ff 8e 80 00 00 00 74 64 e8 d5 43 db fd e8 d0 43 db fd 4c 
RIP  [<ffffffff8359d10c>] l2tp_session_free+0x11c/0x200 net/l2tp/l2tp_core.c:1671
 RSP <ffff8801d99f7b28>
CR2: 0000000000000080
---[ end trace 85ae10db66767a42 ]---