BUG: unable to handle kernel NULL pointer dereference at 0000000000000080
IP: [<ffffffff835aa438>] sock_hold include/net/sock.h:589 [inline]
IP: [<ffffffff835aa438>] l2tp_session_create+0x948/0x1030 net/l2tp/l2tp_core.c:1809
PGD 1cc285067 PUD 1cc0c8067 PMD 0 
Oops: 0002 [#1] PREEMPT SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 0 PID: 15736 Comm: syz-executor5 Not tainted 4.4.151-g37af2ff #85
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801d3c23000 task.stack: ffff8800bafc8000
RIP: 0010:[<ffffffff835aa438>]  [<ffffffff835aa438>] sock_hold include/net/sock.h:589 [inline]
RIP: 0010:[<ffffffff835aa438>]  [<ffffffff835aa438>] l2tp_session_create+0x948/0x1030 net/l2tp/l2tp_core.c:1809
RSP: 0018:ffff8800bafcfb48  EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff8801c8112f00 RCX: ffffc90004896000
RDX: 1ffff10039022610 RSI: ffffffff835a4543 RDI: ffff8801c8113080
RBP: ffff8800bafcfbb8 R08: ffff8801d3c23900 R09: 0000000000000000
R10: 0000000000000000 R11: ffffffff8463a140 R12: ffff8801d22feaa8
R13: ffff8800bafcfcd0 R14: ffff8801d22fea00 R15: ffffffff835a3170
FS:  00007fcde4759700(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000080 CR3: 00000001c846c000 CR4: 00000000001606f0
Stack:
 ffffffff81140a6a ffff8801c8112f20 ffff8801d22feb58 ffff8801d22fea10
 ffffffff838cba90 ffff8801d22feab0 ffff8801d22feb50 ffff8801c8112fe0
 bc0533b900000000 ffff8800a2404c80 0000000000000000 ffff8800a2404cb0
Call Trace:
 [<ffffffff835ae830>] pppol2tp_connect+0x10f0/0x1910 net/l2tp/l2tp_ppp.c:725
 [<ffffffff82f27758>] SYSC_connect+0x1b8/0x300 net/socket.c:1558
 [<ffffffff82f2a094>] SyS_connect+0x24/0x30 net/socket.c:1539
 [<ffffffff838cc125>] 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 [  250.283221] netlink: 3 bytes leftover after parsing attributes in process `syz-executor2'.
netlink: 3 bytes leftover after parsing attributes in process `syz-executor2'.
netlink: 3 bytes leftover after parsing attributes in process `syz-executor2'.
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  [<ffffffff835aa438>] sock_hold include/net/sock.h:589 [inline]
RIP  [<ffffffff835aa438>] l2tp_session_create+0x948/0x1030 net/l2tp/l2tp_core.c:1809
 RSP <ffff8800bafcfb48>
CR2: 0000000000000080
netlink: 4 bytes leftover after parsing attributes in process `syz-executor7'.
netlink: 4 bytes leftover after parsing attributes in process `syz-executor7'.
binder: undelivered TRANSACTION_ERROR: 29201
---[ end trace 0e50c6a76b2dca73 ]---