BUG: unable to handle kernel NULL pointer dereference at 0000000000000080
IP: [<ffffffff835a6f58>] sock_hold include/net/sock.h:589 [inline]
IP: [<ffffffff835a6f58>] l2tp_session_create+0x948/0x1030 net/l2tp/l2tp_core.c:1809
PGD b4a5a067 PUD baf84067 PMD 0 
Oops: 0002 [#1] PREEMPT SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 0 PID: 32230 Comm: syz-executor6 Not tainted 4.4.147-ga5fc665 #16
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801cd0a9800 task.stack: ffff8800b0a68000
RIP: 0010:[<ffffffff835a6f58>]  [<ffffffff835a6f58>] sock_hold include/net/sock.h:589 [inline]
RIP: 0010:[<ffffffff835a6f58>]  [<ffffffff835a6f58>] l2tp_session_create+0x948/0x1030 net/l2tp/l2tp_core.c:1809
RSP: 0018:ffff8800b0a6fad0  EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff8800b9180000 RCX: ffffc9000328b000
RDX: 1ffff10017230030 RSI: ffffffff835a1033 RDI: ffff8800b9180180
RBP: ffff8800b0a6fb40 R08: ffff8801cd0aa100 R09: 0000000000000000
R10: 0000000000000000 R11: ffffffff8463a1e0 R12: ffff8801cac3d9a8
R13: ffff8800b0a6fc58 R14: ffff8801cac3d900 R15: ffffffff8359fc60
FS:  0000000000000000(0000) GS:ffff8801db200000(0063) knlGS:00000000f572ab40
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 0000000000000080 CR3: 00000000a61f9000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff8113fc2a ffff8800b9180020 ffff8801cac3da58 ffff8801cac3d910
 ffffffff838c85b0 ffff8801cac3d9b0 ffff8801cac3da50 ffff8800b91800e0
 ffffffff00000000 ffff8801d06b9100 0000000000000000 ffff8801d06b9130
Call Trace:
 [<ffffffff835ab350>] pppol2tp_connect+0x10f0/0x1910 net/l2tp/l2tp_ppp.c:725
 [<ffffffff82f24298>] SYSC_connect+0x1b8/0x300 net/socket.c:1558
 [<ffffffff82f26bd4>] 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
 [<ffffffff838ca5c3>] 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  [<ffffffff835a6f58>] sock_hold include/net/sock.h:589 [inline]
RIP  [<ffffffff835a6f58>] l2tp_session_create+0x948/0x1030 net/l2tp/l2tp_core.c:1809
 RSP <ffff8800b0a6fad0>
CR2: 0000000000000080
---[ end trace 6eb5cf4c2b7e8efc ]---