BUG: unable to handle kernel NULL pointer dereference at 0000000000000080
IP: [<ffffffff835a67f8>] sock_hold include/net/sock.h:589 [inline]
IP: [<ffffffff835a67f8>] l2tp_session_create+0x948/0x1030 net/l2tp/l2tp_core.c:1809
PGD bb05d067 PUD ad092067 PMD 0 
Oops: 0002 [#1] PREEMPT SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 1 PID: 14790 Comm: syz-executor6 Not tainted 4.4.145-g2241aa9 #78
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8800ad49c800 task.stack: ffff8801d7308000
RIP: 0010:[<ffffffff835a67f8>]  [<ffffffff835a67f8>] sock_hold include/net/sock.h:589 [inline]
RIP: 0010:[<ffffffff835a67f8>]  [<ffffffff835a67f8>] l2tp_session_create+0x948/0x1030 net/l2tp/l2tp_core.c:1809
RSP: 0018:ffff8801d730fb48  EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff8800b7a6e500 RCX: ffffc900050be000
RDX: 1ffff10016f4dcd0 RSI: ffffffff835a08d3 RDI: ffff8800b7a6e680
RBP: ffff8801d730fbb8 R08: ffff8800ad49d100 R09: 0000000000000000
R10: 0000000000000000 R11: ffffffff8463a1e0 R12: ffff8800b7a6f228
R13: ffff8801d730fcd0 R14: ffff8800b7a6f180 R15: ffffffff835a03b0
FS:  00007fdfa6a96700(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000080 CR3: 00000000ae389000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff8113fc2a ffff8800b7a6e520 ffff8800b7a6f2d8 ffff8800b7a6f190
 ffffffff838c7e40 ffff8800b7a6f230 ffff8800b7a6f2d0 ffff8800b7a6e5e0
 5167f42400000000 ffff8800b69aaa80 0000000000000000 ffff8800b69aaab0
Call Trace:
 [<ffffffff835aabf0>] pppol2tp_connect+0x10f0/0x1910 net/l2tp/l2tp_ppp.c:725
 [<ffffffff82f23798>] SYSC_connect+0x1b8/0x300 net/socket.c:1557
 [<ffffffff82f260d4>] SyS_connect+0x24/0x30 net/socket.c:1538
 [<ffffffff838c84e5>] 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 e1 13 
RIP  [<ffffffff835a67f8>] sock_hold include/net/sock.h:589 [inline]
RIP  [<ffffffff835a67f8>] l2tp_session_create+0x948/0x1030 net/l2tp/l2tp_core.c:1809
 RSP <ffff8801d730fb48>
CR2: 0000000000000080
---[ end trace 10645af18e75532a ]---