Dead loop on virtual device ip6tnl0, fix it urgently!
BUG: unable to handle kernel NULL pointer dereference at 0000000000000080
IP: [<ffffffff835a0c38>] sock_hold include/net/sock.h:589 [inline]
IP: [<ffffffff835a0c38>] l2tp_session_create+0x948/0x1030 net/l2tp/l2tp_core.c:1809
PGD ae5f5067 PUD adaf0067 PMD 0 
Oops: 0002 [#1] PREEMPT SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 0 PID: 19342 Comm: syz-executor0 Not tainted 4.4.137-ga2e2217 #59
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801d38f8000 task.stack: ffff8801afb58000
RIP: 0010:[<ffffffff835a0c38>]  [<ffffffff835a0c38>] sock_hold include/net/sock.h:589 [inline]
RIP: 0010:[<ffffffff835a0c38>]  [<ffffffff835a0c38>] l2tp_session_create+0x948/0x1030 net/l2tp/l2tp_core.c:1809
RSP: 0018:ffff8801afb5fad0  EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff8801caa86500 RCX: ffffc90000c30000
RDX: 1ffff10039550cd0 RSI: ffffffff8359ad13 RDI: ffff8801caa86680
RBP: ffff8801afb5fb40 R08: ffff8801d38f8900 R09: 0000000000000000
R10: 0000000000000000 R11: ffffffff84638ce0 R12: ffff8801caa86fa8
R13: ffff8801afb5fc58 R14: ffff8801caa86f00 R15: ffffffff8359a7f0
FS:  0000000000000000(0000) GS:ffff8801db200000(0063) knlGS:00000000f578ab40
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 0000000000000080 CR3: 00000000ad012000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff8113da61 ffff8801caa86520 ffff8801caa87058 ffff8801caa86f10
 ffffffff838c2230 ffff8801caa86fb0 ffff8801caa87050 ffff8801caa865e0
 8d38ca5f00000000 ffff8801baeabb80 0000000000000000 ffff8801baeabbb0
Call Trace:
 [<ffffffff835a5030>] pppol2tp_connect+0x10f0/0x1910 net/l2tp/l2tp_ppp.c:725
 [<ffffffff82f1eca8>] SYSC_connect+0x1b8/0x300 net/socket.c:1557
 [<ffffffff82f215e4>] SyS_connect+0x24/0x30 net/socket.c:1538
 [<ffffffff81006d96>] do_syscall_32_irqs_on arch/x86/entry/common.c:392 [inline]
 [<ffffffff81006d96>] do_fast_syscall_32+0x326/0x8b0 arch/x86/entry/common.c:459
 [<ffffffff838c422a>] sysenter_flags_fixed+0xd/0x17
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  [<ffffffff835a0c38>] sock_hold include/net/sock.h:589 [inline]
RIP  [<ffffffff835a0c38>] l2tp_session_create+0x948/0x1030 net/l2tp/l2tp_core.c:1809
 RSP <ffff8801afb5fad0>
CR2: 0000000000000080
Dead loop on virtual device ip6tnl0, fix it urgently!
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