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 1d8787067 PUD 1d8786067 PMD 0 
Oops: 0002 [#1] PREEMPT SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 1 PID: 11877 Comm: syz-executor3 Not tainted 4.4.152-ge5c5f1f #89
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801bc241800 task.stack: ffff8801cc0c0000
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:ffff8801cc0c7b48  EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff8800ba7d4500 RCX: ffffc900016a1000
RDX: 1ffff100174fa8d0 RSI: ffffffff835a4993 RDI: ffff8800ba7d4680
RBP: ffff8801cc0c7bb8 R08: 000000000000000a R09: 000000000000ffff
R10: ffffed00165a8558 R11: ffffffff8463a140 R12: ffff8800b2d42aa8
R13: ffff8801cc0c7cd0 R14: ffff8800b2d42a00 R15: ffffffff835a35c0
FS:  00007f51a42af700(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000080 CR3: 00000001d2184000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff81140a6a ffff8800ba7d4520 ffff8800b2d42b58 ffff8800b2d42a10
 ffffffff838cbee0 ffff8800b2d42ab0 ffff8800b2d42b50 ffff8800ba7d45e0
 ffffffff00000000 ffff8800a2c69980 0000000000000000 ffff8800a2c699b0
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 <ffff8801cc0c7b48>
CR2: 0000000000000080
---[ end trace 344e70e33fefabc4 ]---