BUG: unable to handle kernel NULL pointer dereference at 0000000000000080
IP: [<ffffffff835a1078>] sock_hold include/net/sock.h:589 [inline]
IP: [<ffffffff835a1078>] l2tp_session_create+0x948/0x1030 net/l2tp/l2tp_core.c:1809
PGD 1d3a50067 PUD 1cc852067 PMD 0 
Oops: 0002 [#1] PREEMPT SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 1 PID: 1778 Comm: syz-executor2 Not tainted 4.4.141-g9664bde #75
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8800ac731800 task.stack: ffff8801c0e30000
RIP: 0010:[<ffffffff835a1078>]  [<ffffffff835a1078>] sock_hold include/net/sock.h:589 [inline]
RIP: 0010:[<ffffffff835a1078>]  [<ffffffff835a1078>] l2tp_session_create+0x948/0x1030 net/l2tp/l2tp_core.c:1809
RSP: 0018:ffff8801c0e37b48  EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff8800b6aaea00 RCX: ffffc900000c7000
RDX: 1ffff10016d55d70 RSI: ffffffff8359b153 RDI: ffff8800b6aaeb80
RBP: ffff8801c0e37bb8 R08: ffff8800ac732100 R09: 0000000000000000
R10: 0000000000000000 R11: ffffffff84638de0 R12: ffff8800b6aaf228
R13: ffff8801c0e37cd0 R14: ffff8800b6aaf180 R15: ffffffff8359ac30
FS:  00007f20192ff700(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000080 CR3: 00000001c9112000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff8113da8a ffff8800b6aaea20 ffff8800b6aaf2d8 ffff8800b6aaf190
 ffffffff838c2670 ffff8800b6aaf230 ffff8800b6aaf2d0 ffff8800b6aaeae0
 a4108dc800000000 ffff8801d3900880 0000000000000000 ffff8801d39008b0
Call Trace:
 [<ffffffff835a5470>] pppol2tp_connect+0x10f0/0x1910 net/l2tp/l2tp_ppp.c:725
 [<ffffffff82f1ec78>] SYSC_connect+0x1b8/0x300 net/socket.c:1557
 [<ffffffff82f215b4>] SyS_connect+0x24/0x30 net/socket.c:1538
 [<ffffffff838c2d25>] 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 91 13 
RIP  [<ffffffff835a1078>] sock_hold include/net/sock.h:589 [inline]
RIP  [<ffffffff835a1078>] l2tp_session_create+0x948/0x1030 net/l2tp/l2tp_core.c:1809
 RSP <ffff8801c0e37b48>
CR2: 0000000000000080
---[ end trace e30ec687aa58a493 ]---