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 1b6343067 [  183.268966] PUD 1cd787067 
Oops: 0002 [#1] PREEMPT SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 0 PID: 15740 Comm: syz-executor5 Not tainted 4.9.124-g09eb2ba #35
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801d6829800 task.stack: ffff8801bfc48000
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:ffff8801bfc4fab0  EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff8801cce8aa00 RCX: 1ffff1003ad0541d
RDX: 1ffff10039fe3e10 RSI: ffff8801d682a0c8 RDI: ffff8801cff1f080
RBP: ffff8801bfc4fb50 R08: ffff8801d682a0e8 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff8801cff1ef58
R13: 0000000000000000 R14: ffff8801cff1ef00 R15: ffff8801bfc4fc68
FS:  0000000000000000(0000) GS:ffff8801db200000(0063) knlGS:00000000f5726b40
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 0000000000000080 CR3: 00000001a4053000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 0000000000000201 ffffffff836c9ec1 ffff8801bfc4fad0 ffffffff812383ad
 ffff8801cff1ef00 ffff8801cce8ab58 ffff8801cff1ef58 ffff8801cce8ab50
 ffff8801cce8aab0 ffff8801cff1ef20 0000000000000000 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
 [<ffffffff81006da7>] do_syscall_32_irqs_on arch/x86/entry/common.c:325 [inline]
 [<ffffffff81006da7>] do_fast_syscall_32+0x2f7/0x870 arch/x86/entry/common.c:387
 [<ffffffff83a030d0>] entry_SYSENTER_compat+0x90/0xa2 arch/x86/entry/entry_64_compat.S:137
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 <ffff8801bfc4fab0>
CR2: 0000000000000080
---[ end trace 6f8140874b6f200f ]---