BUG: unable to handle kernel NULL pointer dereference at 0000000000000080
IP: [<ffffffff8345f5de>] sock_hold include/net/sock.h:589 [inline]
IP: [<ffffffff8345f5de>] l2tp_session_create+0x93e/0x10f0 net/l2tp/l2tp_core.c:1805
PGD 80000001cb416067 PUD 1c90a3067 PMD 0 
Oops: 0002 [#1] PREEMPT SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 1 PID: 3798 Comm: syzkaller260497 Not tainted 4.4.116-g17c7c49 #18
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801c4f2b000 task.stack: ffff8801d01d8000
RIP: 0010:[<ffffffff8345f5de>]  [<ffffffff8345f5de>] sock_hold include/net/sock.h:589 [inline]
RIP: 0010:[<ffffffff8345f5de>]  [<ffffffff8345f5de>] l2tp_session_create+0x93e/0x10f0 net/l2tp/l2tp_core.c:1805
RSP: 0018:ffff8801d01dfad0  EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff8801c5cff680 RCX: ffffffff83458bf6
RDX: 1ffff10038b9ff00 RSI: 0000000000000002 RDI: ffff8801c5cff800
RBP: ffff8801d01dfb40 R08: 000000000000000a R09: 000000000000ffff
R10: ffffffff85700640 R11: ffffffff84418180 R12: ffff8801c6b70d28
R13: ffff8801d01dfc58 R14: ffff8801c5cff760 R15: ffff8801c6b70c80
FS:  0000000000000000(0000) GS:ffff8801db300000(0063) knlGS:00000000f7714b40
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 0000000000000080 CR3: 00000001d9744000 CR4: 0000000000160670
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff8113bd9a ffff8801c5cff6a0 ffff8801c6b70dd8 ffff8801d01dfb00
 ffff8801c6b70c90 0000000000000000 ffff8801c6b70d30 ffff8801c6b70dd0
 ffffffff00000000 0000000000000000 ffff8801c4ab0880 0000000000000000
Call Trace:
 [<ffffffff8346336c>] pppol2tp_connect+0x10fc/0x1930 net/l2tp/l2tp_ppp.c:718
 [<ffffffff82dec676>] SYSC_connect+0x1b6/0x310 net/socket.c:1557
 [<ffffffff82deeee4>] SyS_connect+0x24/0x30 net/socket.c:1538
 [<ffffffff81006d74>] do_syscall_32_irqs_on arch/x86/entry/common.c:390 [inline]
 [<ffffffff81006d74>] do_fast_syscall_32+0x314/0x890 arch/x86/entry/common.c:457
 [<ffffffff837763aa>] 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 4f 07 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 b8 e8 4b 4b 
RIP  [<ffffffff8345f5de>] sock_hold include/net/sock.h:589 [inline]
RIP  [<ffffffff8345f5de>] l2tp_session_create+0x93e/0x10f0 net/l2tp/l2tp_core.c:1805
 RSP <ffff8801d01dfad0>
CR2: 0000000000000080
---[ end trace 06b82ad8d0314d3e ]---
Kernel panic - not syncing: Fatal exception
Dumping ftrace buffer:
   (ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..