BUG: unable to handle kernel NULL pointer dereference at 0000000000000080
kobject: 'rfkill9' (ffff88804bf44e68): kobject_add_internal: parent: 'phy7', set: 'devices'
IP: refcount_dec_and_test arch/x86/include/asm/refcount.h:75 [inline]
IP: sock_put include/net/sock.h:1652 [inline]
IP: l2tp_session_free+0x120/0x210 net/l2tp/l2tp_core.c:1709
PGD 97b51067 P4D 97b51067 PUD 92b59067 PMD 0 
Oops: 0002 [#1] PREEMPT SMP KASAN
PM: Basic memory bitmaps created
Modules linked in:
CPU: 1 PID: 11471 Comm: syz-executor.1 Not tainted 4.14.160-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
kobject: 'rfkill9' (ffff88804bf44e68): kobject_uevent_env
task: ffff8880426b2000 task.stack: ffff8880987d8000
RIP: 0010:refcount_dec_and_test arch/x86/include/asm/refcount.h:75 [inline]
RIP: 0010:sock_put include/net/sock.h:1652 [inline]
RIP: 0010:l2tp_session_free+0x120/0x210 net/l2tp/l2tp_core.c:1709
RSP: 0018:ffff8880987dfc58 EFLAGS: 00010246
RAX: dffffc0000000000 RBX: ffff88809687a280 RCX: 0000000000000000
RDX: 1ffff11012d0f481 RSI: ffff8880426b2880 RDI: ffff88809687a408
RBP: ffff8880987dfc78 R08: ffff8880426b2000 R09: ffff8880426b28a0
R10: 0000000000000000 R11: 0000000000000000 R12: ffff8880a4b7ba40
R13: ffff8880a4b7ba50 R14: 0000000000000000 R15: 0000000000000000
FS:  0000000001a32940(0000) GS:ffff8880aed00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000080 CR3: 000000004c102000 CR4: 00000000001426e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
kobject: 'rfkill9' (ffff88804bf44e68): fill_kobj_path: path = '/devices/virtual/mac80211_hwsim/hwsim7/ieee80211/phy7/rfkill9'
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 l2tp_session_dec_refcount_1 net/l2tp/l2tp_core.h:300 [inline]
 pppol2tp_session_destruct+0xd8/0x110 net/l2tp/l2tp_ppp.c:460
 __sk_destruct+0x4f/0x650 net/core/sock.c:1556
 sk_destruct+0xa4/0xd0 net/core/sock.c:1596
PM: Basic memory bitmaps freed
 __sk_free+0x54/0x230 net/core/sock.c:1604
 sk_free+0x35/0x40 net/core/sock.c:1615
 sock_put include/net/sock.h:1653 [inline]
 pppol2tp_release+0x265/0x310 net/l2tp/l2tp_ppp.c:501
 __sock_release+0xce/0x2b0 net/socket.c:602
ieee80211 phy7: Selected rate control algorithm 'minstrel_ht'
 sock_close+0x1b/0x30 net/socket.c:1139
 __fput+0x275/0x7a0 fs/file_table.c:210
 ____fput+0x16/0x20 fs/file_table.c:244
kobject: 'net' (ffff888089cb1680): kobject_add_internal: parent: 'hwsim7', set: '(null)'
 task_work_run+0x114/0x190 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:191 [inline]
 exit_to_usermode_loop+0x1da/0x220 arch/x86/entry/common.c:164
kobject: 'wlan0' (ffff88804d9e9c30): kobject_add_internal: parent: 'net', set: 'devices'
 prepare_exit_to_usermode arch/x86/entry/common.c:199 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:270 [inline]
 do_syscall_64+0x4bc/0x640 arch/x86/entry/common.c:297
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x4144b1
kobject: 'wlan0' (ffff88804d9e9c30): kobject_uevent_env
RSP: 002b:00007ffd24567840 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000000000000005 RCX: 00000000004144b1
RDX: 0000000000000000 RSI: 0000000000000081 RDI: 0000000000000004
RBP: 0000000000000000 R08: 0000000000761588 R09: ffffffffffffffff
R10: 00007ffd24567910 R11: 0000000000000293 R12: 000000000075bf20
R13: 0000000000000004 R14: 0000000000761590 R15: 000000000075bf2c
Code: 78 fb 48 8d bb 88 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 d9 00 00 00 4c 8b b3 88 01 00 00 <f0> 41 ff 8e 
kobject: 'wlan0' (ffff88804d9e9c30): fill_kobj_path: path = '/devices/virtual/mac80211_hwsim/hwsim7/net/wlan0'
80 00 00 00 0f 88 8b cc 7d 00 74 74 e8 4b a2 78 fb 
RIP: refcount_dec_and_test arch/x86/include/asm/refcount.h:75 [inline] RSP: ffff8880987dfc58
RIP: sock_put include/net/sock.h:1652 [inline] RSP: ffff8880987dfc58
RIP: l2tp_session_free+0x120/0x210 net/l2tp/l2tp_core.c:1709 RSP: ffff8880987dfc58
CR2: 0000000000000080
---[ end trace a33c094adb86b951 ]---
kobject: 'loop5' (ffff8880a41d96e0): kobject_uevent_env