syzbot

BUG: unable to handle kernel NULL pointer dereference at 0000000000000080
IP: [<ffffffff835a93b8>] sock_hold include/net/sock.h:589 [inline]
IP: [<ffffffff835a93b8>] l2tp_session_create+0x948/0x1030 net/l2tp/l2tp_core.c:1809
PGD 1d040d067 PUD 1d063a067 PMD 0 
Oops: 0002 [#1] PREEMPT SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 1 PID: 11792 Comm: syz-executor668 Not tainted 4.4.150-g5541782 #83
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801d2028000 task.stack: ffff8801d39e8000
RIP: 0010:[<ffffffff835a93b8>]  [<ffffffff835a93b8>] sock_hold include/net/sock.h:589 [inline]
RIP: 0010:[<ffffffff835a93b8>]  [<ffffffff835a93b8>] l2tp_session_create+0x948/0x1030 net/l2tp/l2tp_core.c:1809
RSP: 0018:ffff8801d39efb48  EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff8801cecb4780 RCX: 0000000000000000
RDX: 1ffff10039d96920 RSI: ffffffff835a3493 RDI: ffff8801cecb4900
RBP: ffff8801d39efbb8 R08: ffff8801d2028900 R09: 0000000000000000
R10: 0000000000000000 R11: ffffffff8463a140 R12: ffff8800b5a12fa8
R13: ffff8801d39efcd0 R14: ffff8800b5a12f00 R15: ffffffff835a2f70
FS:  00007f82ece40700(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000080 CR3: 00000001d372e000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff8114094a ffff8801cecb47a0 ffff8800b5a13058 ffff8800b5a12f10
 ffffffff838caa10 ffff8800b5a12fb0 ffff8800b5a13050 ffff8801cecb4860
 ffffffff00000000 ffff8801d1d23b80 0000000000000000 ffff8801d1d23bb0
Call Trace:
 [<ffffffff835ad7b0>] pppol2tp_connect+0x10f0/0x1910 net/l2tp/l2tp_ppp.c:725
 [<ffffffff82f266a8>] SYSC_connect+0x1b8/0x300 net/socket.c:1558
 [<ffffffff82f28fe4>] SyS_connect+0x24/0x30 net/socket.c:1539
 [<ffffffff838cb0a5>] 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  [<ffffffff835a93b8>] sock_hold include/net/sock.h:589 [inline]
RIP  [<ffffffff835a93b8>] l2tp_session_create+0x948/0x1030 net/l2tp/l2tp_core.c:1809
 RSP <ffff8801d39efb48>
CR2: 0000000000000080
---[ end trace 77cabc58318453bb ]---