BUG: unable to handle kernel NULL pointer dereference at 0000000000000080
IP: [<ffffffff835a2f18>] sock_hold include/net/sock.h:589 [inline]
IP: [<ffffffff835a2f18>] l2tp_session_create+0x948/0x1030 net/l2tp/l2tp_core.c:1809
PGD 1cff04067 PUD 1d394d067 PMD 0 
Oops: 0002 [#1] PREEMPT SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 0 PID: 6668 Comm: syz-executor1 Not tainted 4.4.141-g8ddb600 #12
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8800a366b000 task.stack: ffff8800a3670000
RIP: 0010:[<ffffffff835a2f18>]  [<ffffffff835a2f18>] sock_hold include/net/sock.h:589 [inline]
RIP: 0010:[<ffffffff835a2f18>]  [<ffffffff835a2f18>] l2tp_session_create+0x948/0x1030 net/l2tp/l2tp_core.c:1809
RSP: 0018:ffff8800a3677ad0  EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff8800aefc4500 RCX: ffffc9000464d000
RDX: 1ffff10015df88d0 RSI: ffffffff8359cff3 RDI: ffff8800aefc4680
RBP: ffff8800a3677b40 R08: ffff8800a366b900 R09: 0000000000000000
R10: 0000000000000000 R11: ffffffff84638f60 R12: ffff8800aefc4328
R13: ffff8800a3677c58 R14: ffff8800aefc4280 R15: ffffffff8359bc20
FS:  0000000000000000(0000) GS:ffff8801db200000(0063) knlGS:00000000f574cb40
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 0000000000000080 CR3: 00000001c9b61000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff8113daa1 ffff8800aefc4520 ffff8800aefc43d8 ffff8800aefc4290
 ffffffff838c4510 ffff8800aefc4330 ffff8800aefc43d0 ffff8800aefc45e0
 a74904fb00000000 ffff8800af442a80 0000000000000000 ffff8800af442ab0
Call Trace:
 [<ffffffff835a7310>] pppol2tp_connect+0x10f0/0x1910 net/l2tp/l2tp_ppp.c:725
 [<ffffffff82f20b18>] SYSC_connect+0x1b8/0x300 net/socket.c:1557
 [<ffffffff82f23454>] SyS_connect+0x24/0x30 net/socket.c:1538
 [<ffffffff81006d96>] do_syscall_32_irqs_on arch/x86/entry/common.c:393 [inline]
 [<ffffffff81006d96>] do_fast_syscall_32+0x326/0x8b0 arch/x86/entry/common.c:460
 [<ffffffff838c64ea>] sysenter_flags_fixed+0xd/0x17
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 91 13 
RIP  [<ffffffff835a2f18>] sock_hold include/net/sock.h:589 [inline]
RIP  [<ffffffff835a2f18>] l2tp_session_create+0x948/0x1030 net/l2tp/l2tp_core.c:1809
 RSP <ffff8800a3677ad0>
CR2: 0000000000000080
device lo entered promiscuous mode
TCP: request_sock_TCPv6: Possible SYN flooding on port 20002. Sending cookies.  Check SNMP counters.
device lo left promiscuous mode
device lo entered promiscuous mode
---[ end trace 52d4c30df29c3291 ]---