BUG: unable to handle kernel NULL pointer dereference at 0000000000000080
IP: [<ffffffff835a6d48>] sock_hold include/net/sock.h:589 [inline]
IP: [<ffffffff835a6d48>] l2tp_session_create+0x948/0x1030 net/l2tp/l2tp_core.c:1809
PGD b2309067 PUD b0cfe067 PMD 0 
Oops: 0002 [#1] PREEMPT SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 1 PID: 7935 Comm: syz-executor4 Not tainted 4.4.146-g1396226 #79
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801bd0a4800 task.stack: ffff8800bba40000
RIP: 0010:[<ffffffff835a6d48>]  [<ffffffff835a6d48>] sock_hold include/net/sock.h:589 [inline]
RIP: 0010:[<ffffffff835a6d48>]  [<ffffffff835a6d48>] l2tp_session_create+0x948/0x1030 net/l2tp/l2tp_core.c:1809
RSP: 0018:ffff8800bba47b48  EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff8800b0ca7b80 RCX: ffffc90006273000
RDX: 1ffff10016194fa0 RSI: ffffffff835a0e23 RDI: ffff8800b0ca7d00
RBP: ffff8800bba47bb8 R08: ffff8801bd0a5100 R09: 0000000000000000
R10: 0000000000000000 R11: ffffffff8463a1e0 R12: ffff8801d88325a8
R13: ffff8800bba47cd0 R14: ffff8801d8832500 R15: ffffffff835a0900
FS:  00007f117126a700(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000080 CR3: 00000000bb154000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff8113fc2a ffff8800b0ca7ba0 ffff8801d8832658 ffff8801d8832510
 ffffffff838c83a0 ffff8801d88325b0 ffff8801d8832650 ffff8800b0ca7c60
 4865272d00000000 ffff8801cc763b80 0000000000000000 ffff8801cc763bb0
Call Trace:
 [<ffffffff835ab140>] pppol2tp_connect+0x10f0/0x1910 net/l2tp/l2tp_ppp.c:725
 [<ffffffff82f240b8>] SYSC_connect+0x1b8/0x300 net/socket.c:1558
 [<ffffffff82f269f4>] SyS_connect+0x24/0x30 net/socket.c:1539
 [<ffffffff838c8a25>] entry_SYSCALL_64_fastpath+0x22/0x9e
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  [<ffffffff835a6d48>] sock_hold include/net/sock.h:589 [inline]
RIP  [<ffffffff835a6d48>] l2tp_session_create+0x948/0x1030 net/l2tp/l2tp_core.c:1809
 RSP <ffff8800bba47b48>
CR2: 0000000000000080
---[ end trace 718745aa40dc6ae9 ]---