======================================
| [   36.712804][   T36] ==================================================================
| [   36.713089][   T36] BUG: KASAN: slab-use-after-free in kobject_put (lib/kobject.c:733)
| [   36.713357][   T36] Read of size 1 at addr ffff888007ba16c4 by task kworker/u18:0/36
| [   36.713596][   T36]
[   36.713695][   T36] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[   36.713699][   T36] Workqueue: l2tp l2tp_session_del_work [l2tp_core]
[   36.713716][   T36] Call Trace:
[   36.713719][   T36]  <TASK>
[   36.713721][   T36]  dump_stack_lvl (lib/dump_stack.c:123)
[   36.713726][   T36]  print_address_description.constprop.0 (mm/kasan/report.c:379)
[   36.713735][   T36]  ? kobject_put (lib/kobject.c:733)
[   36.713739][   T36]  print_report (mm/kasan/report.c:483)
[   36.713742][   T36]  ? kobject_put (lib/kobject.c:733)
[   36.713745][   T36]  ? kasan_addr_to_slab (./include/linux/mm.h:1245 mm/kasan/../slab.h:191 mm/kasan/common.c:47)
[   36.713749][   T36]  ? kobject_put (lib/kobject.c:733)
[   36.713752][   T36]  kasan_report (mm/kasan/report.c:597)
[   36.713756][   T36]  ? kobject_put (lib/kobject.c:733)
[   36.713761][   T36]  kobject_put (lib/kobject.c:733)
[   36.713765][   T36]  netdev_run_todo (./include/linux/list.h:381 net/core/dev.c:11670)
[   36.713773][   T36]  ? generic_xdp_install (net/core/dev.c:11630)
[   36.713776][   T36]  ? unregister_netdevice_many (net/core/dev.c:12241)
[   36.713783][   T36] l2tp_eth_delete (net/l2tp/l2tp_eth.c:158 net/l2tp/l2tp_eth.c:145) l2tp_eth
[   36.713787][   T36] l2tp_session_del_work (net/l2tp/l2tp_core.c:1748) l2tp_core
[   36.713795][   T36]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[   36.713809][   T36]  process_one_work (kernel/workqueue.c:3268)
[   36.713819][   T36]  ? pwq_dec_nr_in_flight (kernel/workqueue.c:3165)
[   36.713825][   T36]  ? assign_work (kernel/workqueue.c:1206)
[   36.713830][   T36]  worker_thread (kernel/workqueue.c:3340 kernel/workqueue.c:3427)
[   36.713835][   T36]  ? rescuer_thread (kernel/workqueue.c:3373)
[   36.713839][   T36]  kthread (kernel/kthread.c:463)
[   36.713843][   T36]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[   36.713846][   T36]  ? ret_from_fork (arch/x86/kernel/process.c:157)
[   36.713856][   T36]  ? __lock_release (kernel/locking/lockdep.c:5536)
[   36.713863][   T36]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[   36.713866][   T36]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[   36.713870][   T36]  ret_from_fork (arch/x86/kernel/process.c:164)
[   36.713872][   T36]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[   36.713875][   T36]  ret_from_fork_asm (arch/x86/entry/entry_64.S:255)
| [   36.732787][   T36] refcount_t: underflow; use-after-free.
| [   36.733002][   T36] WARNING: CPU: 1 PID: 36 at lib/refcount.c:28 refcount_warn_saturate (lib/refcount.c:28 (discriminator 3))
| [   36.733329][   T36] Modules linked in: xfrm_user l2tp_ip6 l2tp_eth l2tp_ip l2tp_netlink l2tp_core
| [   36.734273][   T36] Tainted: [B]=BAD_PAGE
[   36.734481][   T36] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[   36.734923][   T36] Workqueue: l2tp l2tp_session_del_work [l2tp_core]
[   36.735274][   T36] RIP: 0010:refcount_warn_saturate (lib/refcount.c:28 (discriminator 3))
[   36.735614][   T36] Code: cc 38 03 80 fb 01 0f 87 29 33 d7 fe 83 e3 01 0f 85 51 ff ff ff c6 05 17 cc 38 03 01 90 48 c7 c7 40 ba 45 95 e8 62 d6 16 ff 90 <0f> 0b 90 90 e9 33 ff ff ff 48 89 df e8 c0 9d a0 ff e9 ba fe ff ff
All code
========
   0:	cc                   	int3
   1:	38 03                	cmp    %al,(%rbx)
   3:	80 fb 01             	cmp    $0x1,%bl
   6:	0f 87 29 33 d7 fe    	ja     0xfffffffffed73335
   c:	83 e3 01             	and    $0x1,%ebx
   f:	0f 85 51 ff ff ff    	jne    0xffffffffffffff66
  15:	c6 05 17 cc 38 03 01 	movb   $0x1,0x338cc17(%rip)        # 0x338cc33
  1c:	90                   	nop
  1d:	48 c7 c7 40 ba 45 95 	mov    $0xffffffff9545ba40,%rdi
  24:	e8 62 d6 16 ff       	call   0xffffffffff16d68b
  29:	90                   	nop
  2a:*	0f 0b                	ud2		<-- trapping instruction
  2c:	90                   	nop
  2d:	90                   	nop
  2e:	e9 33 ff ff ff       	jmp    0xffffffffffffff66
  33:	48 89 df             	mov    %rbx,%rdi
  36:	e8 c0 9d a0 ff       	call   0xffffffffffa09dfb
  3b:	e9 ba fe ff ff       	jmp    0xfffffffffffffefa

Code starting with the faulting instruction
===========================================
   0:	0f 0b                	ud2
   2:	90                   	nop
   3:	90                   	nop
   4:	e9 33 ff ff ff       	jmp    0xffffffffffffff3c
   9:	48 89 df             	mov    %rbx,%rdi
   c:	e8 c0 9d a0 ff       	call   0xffffffffffa09dd1
  11:	e9 ba fe ff ff       	jmp    0xfffffffffffffed0
[   36.736310][   T36] RSP: 0018:ffffc9000028fb20 EFLAGS: 00010286
[   36.736565][   T36] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
[   36.736893][   T36] RDX: 0000000000000002 RSI: 0000000000000004 RDI: 0000000000000001
[   36.737163][   T36] RBP: 0000000000000003 R08: 0000000000000000 R09: fffffbfff2c80934
[   36.737427][   T36] R10: 0000000000000003 R11: ffffc9000028f6c0 R12: 0000000000000001
[   36.737744][   T36] R13: dffffc0000000000 R14: dead000000000122 R15: dead000000000100
[   36.737979][   T36] FS:  0000000000000000(0000) GS:ffff8880d5788000(0000) knlGS:0000000000000000
[   36.738245][   T36] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   36.738441][   T36] CR2: 0000557d84ae60b8 CR3: 0000000066749002 CR4: 0000000000772ef0
[   36.738751][   T36] PKRU: 55555554
[   36.738875][   T36] Call Trace:
[   36.738994][   T36]  <TASK>
[   36.739073][   T36]  netdev_run_todo (./include/linux/list.h:381 net/core/dev.c:11670)
[   36.739235][   T36]  ? generic_xdp_install (net/core/dev.c:11630)
[   36.739389][   T36]  ? unregister_netdevice_many (net/core/dev.c:12241)
[   36.739552][   T36] l2tp_eth_delete (net/l2tp/l2tp_eth.c:158 net/l2tp/l2tp_eth.c:145) l2tp_eth
[   36.739789][   T36] l2tp_session_del_work (net/l2tp/l2tp_core.c:1748) l2tp_core
[   36.739987][   T36]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[   36.740145][   T36]  process_one_work (kernel/workqueue.c:3268)
[   36.740317][   T36]  ? pwq_dec_nr_in_flight (kernel/workqueue.c:3165)
[   36.740489][   T36]  ? assign_work (kernel/workqueue.c:1206)
[   36.740650][   T36]  worker_thread (kernel/workqueue.c:3340 kernel/workqueue.c:3427)
[   36.740875][   T36]  ? rescuer_thread (kernel/workqueue.c:3373)
[   36.741031][   T36]  kthread (kernel/kthread.c:463)
[   36.741156][   T36]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[   36.741308][   T36]  ? ret_from_fork (arch/x86/kernel/process.c:157)
[   36.741462][   T36]  ? __lock_release (kernel/locking/lockdep.c:5536)
[   36.741933][   T36]  ? rcu_is_watching (./include/linux/context_tracking.h:128 kernel/rcu/tree.c:751)
[   36.742086][   T36]  ? kthread_is_per_cpu (kernel/kthread.c:412)
[   36.742241][   T36]  ret_from_fork (arch/x86/kernel/process.c:164)
[   36.742393][   T36]  ? kthread_is_per_cpu (kernel/kthread.c:412)


Finger prints:
print_report:kasan_report:kobject_put:netdev_run_todo:l2tp_eth_delete
refcount_warn_saturate:netdev_run_todo:l2tp_eth_delete:l2tp_session_del_work:process_one_work