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kernel BUG at net/l2tp/l2tp_core.c:917!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 0 PID: 6282 Comm: syz-executor4 Not tainted 4.9.113-g8956c50 #67
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801cefbe000 task.stack: ffff8801d3a50000
RIP: 0010:[<ffffffff836bbe20>]  [<ffffffff836bbe20>] l2tp_session_queue_purge+0xe0/0x100 net/l2tp/l2tp_core.c:917
RSP: 0018:ffff8801d3a57d50  EFLAGS: 00010212
RAX: 0000000000040000 RBX: ffff8801cd5de000 RCX: ffffc90007744000
RDX: 0000000000000105 RSI: ffffffff836bbe20 RDI: ffff8801cd5de000
RBP: ffff8801d3a57d78 R08: ffff8801cefbe8e8 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff8801cd5de000
R13: ffff8801cbf66660 R14: ffff8801cdf3ad58 R15: ffffffff83013be0
FS:  00007f5e11bb0700(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b33729000 CR3: 00000001cf582000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffff8801cdf3aa80 ffff8801cd5de000 ffff8801cbf66660 ffff8801cdf3ad58
 ffffffff83013be0 ffff8801d3a57da8 ffffffff836c7abb ffff8801cbf66640
 ffffffff8417b160 ffff8801cbf66668 0000000000000000 ffff8801d3a57dd8
Call Trace:
 [<ffffffff836c7abb>] pppol2tp_release+0x1fb/0x2e0 net/l2tp/l2tp_ppp.c:492
 [<ffffffff83013ab6>] sock_release+0x96/0x1c0 net/socket.c:599
 [<ffffffff83013bf6>] sock_close+0x16/0x20 net/socket.c:1046
 [<ffffffff815782e3>] __fput+0x263/0x700 fs/file_table.c:208
 [<ffffffff81578805>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff8119838c>] task_work_run+0x10c/0x180 kernel/task_work.c:116
 [<ffffffff8100559c>] tracehook_notify_resume include/linux/tracehook.h:191 [inline]
 [<ffffffff8100559c>] exit_to_usermode_loop+0xfc/0x120 arch/x86/entry/common.c:161
 [<ffffffff810064d4>] prepare_exit_to_usermode arch/x86/entry/common.c:191 [inline]
 [<ffffffff810064d4>] syscall_return_slowpath arch/x86/entry/common.c:260 [inline]
 [<ffffffff810064d4>] do_syscall_64+0x364/0x490 arch/x86/entry/common.c:287
 [<ffffffff839fa193>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb
Code: 2c ca fd 31 c0 5b 41 5c 41 5d 41 5e 41 5f 5d c3 e8 66 2c ca fd 48 89 df e8 0e 7c 34 00 eb ca e8 57 2c ca fd 0f 0b e8 50 2c ca fd <0f> 0b 4c 89 ff e8 f6 fd e7 fd eb a6 48 89 df e8 cc fd e7 fd e9 
RIP  [<ffffffff836bbe20>] l2tp_session_queue_purge+0xe0/0x100 net/l2tp/l2tp_core.c:917
 RSP <ffff8801d3a57d50>
---[ end trace 8ccaed7ab82844a5 ]---