TCP: request_sock_TCPv6: Possible SYN flooding on port 20002. Sending cookies.  Check SNMP counters.
BUG: unable to handle kernel NULL pointer dereference at 0000000000000080
IP: [<ffffffff836c8bb0>] sock_hold include/net/sock.h:584 [inline]
IP: [<ffffffff836c8bb0>] l2tp_session_create+0xc60/0x16f0 net/l2tp/l2tp_core.c:1911
PGD 1da0f1067 [  198.199571] PUD 1d8fb5067 
Oops: 0002 [#1] PREEMPT SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 0 PID: 15568 Comm: syz-executor4 Not tainted 4.9.124-g09eb2ba #83
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801bfc98000 task.stack: ffff8801b6340000
RIP: 0010:[<ffffffff836c8bb0>]  [<ffffffff836c8bb0>] sock_hold include/net/sock.h:584 [inline]
RIP: 0010:[<ffffffff836c8bb0>]  [<ffffffff836c8bb0>] l2tp_session_create+0xc60/0x16f0 net/l2tp/l2tp_core.c:1911
RSP: 0018:ffff8801b6347ac0  EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff8801bd2f4a00 RCX: 1ffff10037f9311d
RDX: 1ffff10038d9e350 RSI: ffff8801bfc988c8 RDI: ffff8801c6cf1a80
RBP: ffff8801b6347b60 R08: ffff8801bfc988e8 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff8801c6cf1958
R13: 0000000000000000 R14: ffff8801c6cf1900 R15: 0000000000000000
FS:  00007f28c3ebe700(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000080 CR3: 00000001ac7aa000 CR4: 00000000001606f0
Stack:
 ffffffff836c8e27 ffffffff836c9ec1 ffff8801a559cc48 0000000000000000
 ffff8801c6cf1900 ffff8801bd2f4b58 ffff8801c6cf1958 ffff8801bd2f4b50
 ffff8801bd2f4ab0 ffff8801c6cf1920 ffff8801a559c400 0000000000000000
Call Trace:
 [<ffffffff836cdd67>] pppol2tp_connect+0x10d7/0x18f0 net/l2tp/l2tp_ppp.c:718
 [<ffffffff8301ea38>] SYSC_connect+0x1b8/0x300 net/socket.c:1575
 [<ffffffff83021314>] SyS_connect+0x24/0x30 net/socket.c:1556
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff83a019d3>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb
Code: 00 00 49 8d be 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 7b 09 00 00 49 8b 86 80 01 00 00 <f0> ff 80 80 00 00 00 48 b8 00 00 00 00 00 fc ff df 48 8b 55 d0 
RIP  [<ffffffff836c8bb0>] sock_hold include/net/sock.h:584 [inline]
RIP  [<ffffffff836c8bb0>] l2tp_session_create+0xc60/0x16f0 net/l2tp/l2tp_core.c:1911
 RSP <ffff8801b6347ac0>
CR2: 0000000000000080
---[ end trace 956ae35d699eea8f ]---