BUG: unable to handle kernel NULL pointer dereference at 0000000000000080
IP: [<ffffffff835aa888>] sock_hold include/net/sock.h:589 [inline]
IP: [<ffffffff835aa888>] l2tp_session_create+0x948/0x1030 net/l2tp/l2tp_core.c:1809
PGD 1d6059067 PUD 1cb920067 PMD 0 
Oops: 0002 [#1] PREEMPT SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 1 PID: 4140 Comm: syz-executor5 Not tainted 4.4.152-ge5c5f1f #89
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801d8774800 task.stack: ffff8801bca08000
RIP: 0010:[<ffffffff835aa888>]  [<ffffffff835aa888>] sock_hold include/net/sock.h:589 [inline]
RIP: 0010:[<ffffffff835aa888>]  [<ffffffff835aa888>] l2tp_session_create+0x948/0x1030 net/l2tp/l2tp_core.c:1809
RSP: 0018:ffff8801bca0fb48  EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff8801d70c7180 RCX: ffffc90007056000
RDX: 1ffff1003ae18e60 RSI: ffffffff835a4993 RDI: ffff8801d70c7300
RBP: ffff8801bca0fbb8 R08: 000000000000000a R09: 000000000000ffff
R10: ffffed0039409558 R11: ffffffff8463a140 R12: ffff8801ca04aaa8
R13: ffff8801bca0fcd0 R14: ffff8801ca04aa00 R15: ffffffff835a35c0
FS:  00007f3f0f8a4700(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000080 CR3: 00000001ca5e8000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff81140a6a ffff8801d70c71a0 ffff8801ca04ab58 ffff8801ca04aa10
 ffffffff838cbee0 ffff8801ca04aab0 ffff8801ca04ab50 ffff8801d70c7260
 ffffffff00000000 ffff8801d07c6e80 0000000000000000 ffff8801d07c6eb0
Call Trace:
 [<ffffffff835aec80>] pppol2tp_connect+0x10f0/0x1910 net/l2tp/l2tp_ppp.c:725
 [<ffffffff82f27bf8>] SYSC_connect+0x1b8/0x300 net/socket.c:1570
 [<ffffffff82f2a544>] SyS_connect+0x24/0x30 net/socket.c:1551
 [<ffffffff838cc565>] 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  [<ffffffff835aa888>] sock_hold include/net/sock.h:589 [inline]
RIP  [<ffffffff835aa888>] l2tp_session_create+0x948/0x1030 net/l2tp/l2tp_core.c:1809
 RSP <ffff8801bca0fb48>
CR2: 0000000000000080
---[ end trace 24fc0466b63b0d37 ]---