BUG: unable to handle kernel NULL pointer dereference at 0000000000000080 IP: [] l2tp_session_free+0x11c/0x200 net/l2tp/l2tp_core.c:1671 PGD 1b9263067 PUD 1d6cdb067 PMD 0 Oops: 0002 [#1] PREEMPT SMP KASAN Dumping ftrace buffer: (ftrace buffer empty) Modules linked in: CPU: 0 PID: 7879 Comm: syz-executor2 Not tainted 4.4.147-ga5fc665 #80 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 task: ffff8801b9e4c800 task.stack: ffff8801d7dc0000 RIP: 0010:[] [] l2tp_session_free+0x11c/0x200 net/l2tp/l2tp_core.c:1671 RSP: 0018:ffff8801d7dc7cd8 EFLAGS: 00010246 RAX: dffffc0000000000 RBX: ffff8801d4f6f680 RCX: ffffc90001410000 RDX: 1ffff100172866b0 RSI: ffffffff835a3531 RDI: ffff8800b9433580 RBP: ffff8801d7dc7cf8 R08: ffffffff85304470 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000000 R12: ffff8800b9433400 R13: ffff8801d4f6f688 R14: 0000000000000000 R15: ffffffff82f1f9a0 FS: 00007f871408c700(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000080 CR3: 00000001b9860000 CR4: 00000000001606f0 Stack: ffff8801d6f78000 ffff8801d4f6f680 ffff8801d6f783d0 ffff8801d6f782d8 ffff8801d7dc7d20 ffffffff835acfd7 ffff8801d6f78000 ffffffff835acf00 ffff8800abaecce0 ffff8801d7dc7d48 ffffffff82f34a2c ffff8801d6f78000 Call Trace: [] l2tp_session_dec_refcount_1 net/l2tp/l2tp_core.h:293 [inline] [] pppol2tp_session_destruct+0xd7/0x110 net/l2tp/l2tp_ppp.c:477 [] sk_destruct+0x4c/0x4c0 net/core/sock.c:1447 [] __sk_free+0x4f/0x220 net/core/sock.c:1480 [] sk_free+0x30/0x40 net/core/sock.c:1491 [] sock_put include/net/sock.h:1639 [inline] [] pppol2tp_release+0x26a/0x310 net/l2tp/l2tp_ppp.c:518 [] sock_release+0x96/0x1c0 net/socket.c:587 [] sock_close+0x16/0x20 net/socket.c:1038 [] __fput+0x235/0x6f0 fs/file_table.c:208 [] ____fput+0x15/0x20 fs/file_table.c:244 [] task_work_run+0x10f/0x190 kernel/task_work.c:115 [] tracehook_notify_resume include/linux/tracehook.h:191 [inline] [] exit_to_usermode_loop+0x13d/0x160 arch/x86/entry/common.c:253 [] prepare_exit_to_usermode arch/x86/entry/common.c:284 [inline] [] syscall_return_slowpath+0x1b5/0x1f0 arch/x86/entry/common.c:349 [] int_ret_from_sys_call+0x25/0xa3 Code: 49 8d bc 24 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 d0 00 00 00 4d 8b b4 24 80 01 00 00 41 ff 8e 80 00 00 00 74 64 e8 55 02 db fd e8 50 02 db fd 4c RIP [] l2tp_session_free+0x11c/0x200 net/l2tp/l2tp_core.c:1671 RSP CR2: 0000000000000080 ---[ end trace e195532863407e8c ]---