[<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
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 ad421067 PUD b9b63067 PMD 0 
Oops: 0002 [#1] PREEMPT SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 0 PID: 7079 Comm: syz-executor5 Not tainted 4.4.147-ga5fc665 #16
PF_BRIDGE: RTM_SETLINK with unknown ifindex
PF_BRIDGE: RTM_SETLINK with unknown ifindex
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8800b990b000 task.stack: ffff8800ad940000
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:ffff8800ad947ad0  EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff8800ba968f00 RCX: ffffc900082fb000
RDX: 1ffff1001752d210 RSI: ffffffff835a1033 RDI: ffff8800ba969080
RBP: ffff8800ad947b40 R08: ffff8800b990b900 R09: 0000000000000000
R10: 0000000000000000 R11: ffffffff8463a1e0 R12: ffff8800ba968aa8
R13: ffff8800ad947c58 R14: ffff8800ba968a00 R15: ffffffff8359fc60
FS:  0000000000000000(0000) GS:ffff8801db200000(0063) knlGS:00000000f577cb40
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 0000000000000080 CR3: 00000000bb116000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff8113fc2a ffff8800ba968f20 ffff8800ba968b58 ffff8800ba968a10
 ffffffff838c85b0 ffff8800ba968ab0 ffff8800ba968b50 ffff8800ba968fe0
 ffffffff00000000 ffff8800b8ebe600 0000000000000000 ffff8800b8ebe630
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 <ffff8800ad947ad0>
CR2: 0000000000000080
FAULT_FLAG_ALLOW_RETRY missing 30
CPU: 1 PID: 7069 Comm: syz-executor1 Tainted: G      D         4.4.147-ga5fc665 #16
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 0000000000000000 c2cd4875c8ace335 ffff8801ce647690 ffffffff81e12a4d
 ffff8800b664ea80 ffff8801ce647818 1ffff10039cc8edf 0000000000000002
 0000000000000000 ffff8801ce647840 ffffffff81c15914 ffffffff812312c0
Call Trace:
 [<ffffffff81e12a4d>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81e12a4d>] dump_stack+0xc1/0x124 lib/dump_stack.c:51
 [<ffffffff81c15914>] handle_userfault.cold.18+0x22/0x27 fs/userfaultfd.c:316
 [<ffffffff8149f91a>] do_anonymous_page mm/memory.c:2746 [inline]
 [<ffffffff8149f91a>] handle_pte_fault mm/memory.c:3312 [inline]
 [<ffffffff8149f91a>] __handle_mm_fault mm/memory.c:3443 [inline]
 [<ffffffff8149f91a>] handle_mm_fault+0x269a/0x30b0 mm/memory.c:3472
 [<ffffffff810d9ad5>] __do_page_fault+0x365/0xa10 arch/x86/mm/fault.c:1245
 [<ffffffff810da1a7>] do_page_fault+0x27/0x30 arch/x86/mm/fault.c:1308
 [<ffffffff838ca048>] page_fault+0x28/0x30 arch/x86/entry/entry_64.S:1037
---[ end trace 70212990e1346b32 ]---