l2tp_core: tunl 4: sockfd_lookup(fd=5) returned -9
BUG: unable to handle kernel NULL pointer dereference at 0000000000000080
IP: [<ffffffff835aa438>] sock_hold include/net/sock.h:589 [inline]
IP: [<ffffffff835aa438>] l2tp_session_create+0x948/0x1030 net/l2tp/l2tp_core.c:1809
PGD b5fc4067 PUD b917a067 PMD 0 
Oops: 0002 [#1] PREEMPT SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 0 PID: 16480 Comm: syz-executor0 Not tainted 4.4.151-ge917467 #20
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8800b7498000 task.stack: ffff8800af8e0000
RIP: 0010:[<ffffffff835aa438>]  [<ffffffff835aa438>] sock_hold include/net/sock.h:589 [inline]
RIP: 0010:[<ffffffff835aa438>]  [<ffffffff835aa438>] l2tp_session_create+0x948/0x1030 net/l2tp/l2tp_core.c:1809
RSP: 0018:ffff8800af8e7ad0  EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff8800b2b7e780 RCX: 0000000000000006
RDX: 1ffff1001656fd20 RSI: ffffffff835a4543 RDI: ffff8800b2b7e900
RBP: ffff8800af8e7b40 R08: ffff8800b7498900 R09: 0000000000000000
R10: 0000000000000000 R11: ffffffff8463a140 R12: ffff8801d1de1728
R13: ffff8800af8e7c58 R14: ffff8801d1de1680 R15: ffffffff835a3170
FS:  0000000000000000(0000) GS:ffff8801db200000(0063) knlGS:00000000f771db40
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 0000000000000080 CR3: 00000000ba93c000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff81140a6a ffff8800b2b7e7a0 ffff8801d1de17d8 ffff8801d1de1690
 ffffffff838cba90 ffff8801d1de1730 ffff8801d1de17d0 ffff8800b2b7e860
 ffffffff00000000 ffff8801cf196600 0000000000000000 ffff8801cf196630
Call Trace:
 [<ffffffff835ae830>] pppol2tp_connect+0x10f0/0x1910 net/l2tp/l2tp_ppp.c:725
 [<ffffffff82f27758>] SYSC_connect+0x1b8/0x300 net/socket.c:1558
 [<ffffffff82f2a094>] SyS_connect+0x24/0x30 net/socket.c:1539
 [<ffffffff81006d94>] do_syscall_32_irqs_on arch/x86/entry/common.c:393 [inline]
 [<ffffffff81006d94>] do_fast_syscall_32+0x324/0x8b0 arch/x86/entry/common.c:460
 [<ffffffff838cda83>] sysenter_flags_fixed+0xd/0x1a
Code: 00 00 48 8d bb 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 36 06 00 00 48 8b 83 80 01 00 00 <f0> ff 80 80 00 00 00 48 8d 43 20 48 89 c7 48 89 45 b0 e8 f1 13 
RIP  [<ffffffff835aa438>] sock_hold include/net/sock.h:589 [inline]
RIP  [<ffffffff835aa438>] l2tp_session_create+0x948/0x1030 net/l2tp/l2tp_core.c:1809
 RSP <ffff8800af8e7ad0>
CR2: 0000000000000080
---[ end trace e9d7be6b6c172b5e ]---