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 ac588067 PUD adb43067 PMD 0 
Oops: 0002 [#1] PREEMPT SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 0 PID: 6875 Comm: syz-executor1 Not tainted 4.4.145-g2241aa9 #14
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8800a220b000 task.stack: ffff8800a2288000
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:ffff8800a228fad0  EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff8801d477a500 RCX: ffffc90004e99000
RDX: 1ffff1003a8ef4d0 RSI: ffffffff835a08d3 RDI: ffff8801d477a680
RBP: ffff8800a228fb40 R08: ffff8800a220b900 R09: 0000000000000000
R10: 0000000000000000 R11: ffffffff8463a1e0 R12: ffff8800b6b95c28
R13: ffff8800a228fc58 R14: ffff8800b6b95b80 R15: ffffffff835a03b0
FS:  0000000000000000(0000) GS:ffff8801db200000(0063) knlGS:00000000f574eb40
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 0000000000000080 CR3: 00000000b9875000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff8113fc2a ffff8801d477a520 ffff8800b6b95cd8 ffff8800b6b95b90
 ffffffff838c7e40 ffff8800b6b95c30 ffff8800b6b95cd0 ffff8801d477a5e0
 ffffffff00000000 ffff8800ac429980 0000000000000000 ffff8800ac4299b0
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
 [<ffffffff81006d94>] do_syscall_32_irqs_on arch/x86/entry/common.c:393 [inline]
 [<ffffffff81006d94>] do_fast_syscall_32+0x324/0x8b0 arch/x86/entry/common.c:460
 [<ffffffff838c9e43>] sysenter_flags_fixed+0xd/0x1a
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 <ffff8800a228fad0>
CR2: 0000000000000080
---[ end trace 077cfdb0eec56848 ]---