BUG: unable to handle kernel NULL pointer dereference at 0000000000000080
IP: [<ffffffff835a0b08>] sock_hold include/net/sock.h:589 [inline]
IP: [<ffffffff835a0b08>] l2tp_session_create+0x948/0x1030 net/l2tp/l2tp_core.c:1809
PGD 1d8023067 PUD 1d846b067 PMD 0 
Oops: 0002 [#1] PREEMPT SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 0 PID: 4620 Comm: syz-executor056 Not tainted 4.4.140-g789274d #67
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801d7843000 task.stack: ffff8801d7260000
RIP: 0010:[<ffffffff835a0b08>]  [<ffffffff835a0b08>] sock_hold include/net/sock.h:589 [inline]
RIP: 0010:[<ffffffff835a0b08>]  [<ffffffff835a0b08>] l2tp_session_create+0x948/0x1030 net/l2tp/l2tp_core.c:1809
RSP: 0018:ffff8801d7267b48  EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff8801cf5fdb80 RCX: 0000000000000006
RDX: 1ffff10039ebfba0 RSI: ffffffff8359abe3 RDI: ffff8801cf5fdd00
RBP: ffff8801d7267bb8 R08: ffff8801d7843900 R09: 0000000000000000
R10: 0000000000000000 R11: ffffffff84638de0 R12: ffff8801d6e80d28
R13: ffff8801d7267cd0 R14: ffff8801d6e80c80 R15: ffffffff83599810
FS:  00007fee9ea05700(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000080 CR3: 00000001d87f2000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff8113da8a ffff8801cf5fdba0 ffff8801d6e80dd8 ffff8801d6e80c90
 ffffffff838c2100 ffff8801d6e80d30 ffff8801d6e80dd0 ffff8801cf5fdc60
 ffffffff00000000 ffff8801d79d8880 0000000000000000 ffff8801d79d88b0
Call Trace:
 [<ffffffff835a4f00>] pppol2tp_connect+0x10f0/0x1910 net/l2tp/l2tp_ppp.c:725
 [<ffffffff82f1e828>] SYSC_connect+0x1b8/0x300 net/socket.c:1557
 [<ffffffff82f21164>] SyS_connect+0x24/0x30 net/socket.c:1538
 [<ffffffff838c27a5>] 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 91 13 
RIP  [<ffffffff835a0b08>] sock_hold include/net/sock.h:589 [inline]
RIP  [<ffffffff835a0b08>] l2tp_session_create+0x948/0x1030 net/l2tp/l2tp_core.c:1809
 RSP <ffff8801d7267b48>
CR2: 0000000000000080
---[ end trace 96360d70ad2be9cc ]---