==================================================================
BUG: KASAN: use-after-free in rcu_cblist_dequeue+0x6c/0xb0 kernel/rcu/rcu_segcblist.c:75
Read of size 8 at addr ffff88813255d590 by task syz.9.1071/4454

CPU: 1 PID: 4454 Comm: syz.9.1071 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
 <IRQ>
 __dump_stack+0x21/0x24 lib/dump_stack.c:88
 dump_stack_lvl+0x110/0x170 lib/dump_stack.c:106
 print_address_description+0x71/0x200 mm/kasan/report.c:316
 print_report+0x4a/0x60 mm/kasan/report.c:420
 kasan_report+0x122/0x150 mm/kasan/report.c:524
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report_generic.c:351
 rcu_cblist_dequeue+0x6c/0xb0 kernel/rcu/rcu_segcblist.c:75
 rcu_do_batch+0x4bc/0xc30 kernel/rcu/tree.c:2285
 rcu_core+0x486/0xf00 kernel/rcu/tree.c:2557
 rcu_core_si+0x9/0x10 kernel/rcu/tree.c:2574
 handle_softirqs+0x1d7/0x600 kernel/softirq.c:642
 __do_softirq kernel/softirq.c:680 [inline]
 invoke_softirq kernel/softirq.c:497 [inline]
 __irq_exit_rcu+0x52/0xf0 kernel/softirq.c:729
 irq_exit_rcu+0x9/0x10 kernel/softirq.c:741
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1118 [inline]
 sysvec_apic_timer_interrupt+0xa9/0xc0 arch/x86/kernel/apic/apic.c:1118
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1b/0x20 arch/x86/include/asm/idtentry.h:691
RIP: 0010:clear_page_erms+0x7/0x10 arch/x86/lib/clear_page_64.S:50
Code: 48 89 47 18 48 89 47 20 48 89 47 28 48 89 47 30 48 89 47 38 48 8d 7f 40 75 d9 90 c3 90 90 90 90 90 90 90 b9 00 10 00 00 31 c0 <f3> aa c3 90 90 90 90 90 90 89 c8 48 c1 e9 03 74 18 0f 1f 84 00 00
RSP: 0018:ffffc9000299f5f0 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffffea00044588c0 RCX: 0000000000000f00
RDX: ffffc900029f9000 RSI: 000000000007ffff RDI: ffff888111623100
RBP: ffffc9000299f740 R08: ffffea00044588c7 R09: 1ffffd400088b118
R10: dffffc0000000000 R11: fffff9400088b119 R12: 0000000000000000
R13: ffff888111623000 R14: 0000000000000000 R15: ffff888118eed390
 shmem_fault+0x1ab/0x670 mm/shmem.c:2166
 __do_fault mm/memory.c:4376 [inline]
 do_read_fault mm/memory.c:4751 [inline]
 do_fault+0x19de/0x1e30 mm/memory.c:4887
 handle_pte_fault mm/memory.c:5183 [inline]
 __handle_mm_fault mm/memory.c:5325 [inline]
 handle_mm_fault+0x1363/0x26b0 mm/memory.c:5465
 faultin_page mm/gup.c:1026 [inline]
 __get_user_pages+0x34b/0xdb0 mm/gup.c:1250
 populate_vma_page_range mm/gup.c:1607 [inline]
 __mm_populate+0x2ea/0x430 mm/gup.c:1721
 mm_populate include/linux/mm.h:3148 [inline]
 vm_mmap_pgoff+0x271/0x3f0 mm/util.c:530
 ksys_mmap_pgoff+0xf6/0x1d0 mm/mmap.c:1537
 __do_sys_mmap arch/x86/kernel/sys_x86_64.c:93 [inline]
 __se_sys_mmap arch/x86/kernel/sys_x86_64.c:86 [inline]
 __x64_sys_mmap+0xfa/0x110 arch/x86/kernel/sys_x86_64.c:86
 x64_sys_call+0x8fd/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:10
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f983db9e159
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f983e994028 EFLAGS: 00000246 ORIG_RAX: 0000000000000009
RAX: ffffffffffffffda RBX: 00007f983de25fa0 RCX: 00007f983db9e159
RDX: b635773f06ebbeee RSI: 0000000000b36000 RDI: 0000200000000000
RBP: 00007f983dc3506b R08: ffffffffffffffff R09: 0000000000000000
R10: 0000000000008031 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f983de26038 R14: 00007f983de25fa0 R15: 00007ffdbbd6aa38
 </TASK>

Allocated by task 4438:
 kasan_save_stack mm/kasan/common.c:46 [inline]
 kasan_set_track+0x4b/0x70 mm/kasan/common.c:53
 kasan_save_alloc_info+0x1f/0x30 mm/kasan/generic.c:505
 ____kasan_kmalloc mm/kasan/common.c:380 [inline]
 __kasan_kmalloc+0x95/0xb0 mm/kasan/common.c:389
 kasan_kmalloc include/linux/kasan.h:212 [inline]
 __do_kmalloc_node mm/slab_common.c:938 [inline]
 __kmalloc+0xb4/0x1e0 mm/slab_common.c:951
 kmalloc include/linux/slab.h:568 [inline]
 kzalloc include/linux/slab.h:699 [inline]
 l2tp_session_create+0x38/0xbd0 net/l2tp/l2tp_core.c:1614
 pppol2tp_connect+0xbf5/0x1640 net/l2tp/l2tp_ppp.c:771
 __sys_connect_file net/socket.c:2001 [inline]
 __sys_connect+0x3da/0x460 net/socket.c:2018
 __do_sys_connect net/socket.c:2028 [inline]
 __se_sys_connect net/socket.c:2025 [inline]
 __x64_sys_connect+0x7a/0x90 net/socket.c:2025
 x64_sys_call+0x88d/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:43
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

Freed by task 874:
 kasan_save_stack mm/kasan/common.c:46 [inline]
 kasan_set_track+0x4b/0x70 mm/kasan/common.c:53
 kasan_save_free_info+0x2b/0x40 mm/kasan/generic.c:516
 ____kasan_slab_free+0x132/0x180 mm/kasan/common.c:242
 __kasan_slab_free+0x11/0x20 mm/kasan/common.c:250
 kasan_slab_free include/linux/kasan.h:178 [inline]
 slab_free_hook mm/slub.c:1750 [inline]
 slab_free_freelist_hook+0xc2/0x190 mm/slub.c:1776
 slab_free mm/slub.c:3712 [inline]
 __kmem_cache_free+0xb7/0x1b0 mm/slub.c:3728
 kfree+0x6f/0xf0 mm/slab_common.c:990
 l2tp_session_free net/l2tp/l2tp_core.c:168 [inline]
 l2tp_session_put+0xaf/0x1a0 net/l2tp/l2tp_core.c:193
 l2tp_session_delete+0x3df/0x4d0 net/l2tp/l2tp_core.c:1587
 l2tp_tunnel_closeall net/l2tp/l2tp_core.c:1233 [inline]
 l2tp_tunnel_del_work+0x199/0x410 net/l2tp/l2tp_core.c:1271
 process_one_work+0x717/0xc30 kernel/workqueue.c:2302
 worker_thread+0xa4d/0x11d0 kernel/workqueue.c:2449
 kthread+0x281/0x320 kernel/kthread.c:386
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

Last potentially related work creation:
 kasan_save_stack+0x3a/0x60 mm/kasan/common.c:46
 __kasan_record_aux_stack+0xb6/0xc0 mm/kasan/generic.c:486
 kasan_record_aux_stack_noalloc+0xb/0x10 mm/kasan/generic.c:496
 __call_rcu_common kernel/rcu/tree.c:2807 [inline]
 call_rcu+0xcf/0xf50 kernel/rcu/tree.c:2926
 pppol2tp_release+0x1e3/0x2b0 net/l2tp/l2tp_ppp.c:446
 __sock_release net/socket.c:652 [inline]
 sock_close+0xc9/0x220 net/socket.c:1390
 __fput+0x1fd/0x8f0 fs/file_table.c:320
 ____fput+0x15/0x20 fs/file_table.c:348
 task_work_run+0x1e1/0x250 kernel/task_work.c:203
 exit_task_work include/linux/task_work.h:39 [inline]
 do_exit+0xb0d/0x29f0 kernel/exit.c:896
 __do_sys_exit kernel/exit.c:1006 [inline]
 __se_sys_exit kernel/exit.c:1004 [inline]
 __cfi___ia32_sys_exit+0x0/0x10 kernel/exit.c:1004
 x64_sys_call+0x67/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:61
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

Second to last potentially related work creation:
 kasan_save_stack+0x3a/0x60 mm/kasan/common.c:46
 __kasan_record_aux_stack+0xb6/0xc0 mm/kasan/generic.c:486
 kasan_record_aux_stack_noalloc+0xb/0x10 mm/kasan/generic.c:496
 kvfree_call_rcu+0x8b/0x7a0 kernel/rcu/tree.c:3445
 drop_sysctl_table+0x2f5/0x430 fs/proc/proc_sysctl.c:1731
 drop_sysctl_table+0x2e4/0x430 fs/proc/proc_sysctl.c:1734
 unregister_sysctl_table+0x75/0x120 fs/proc/proc_sysctl.c:1769
 unregister_net_sysctl_table+0x15/0x20 net/sysctl_net.c:175
 neigh_sysctl_unregister+0x78/0x90 net/core/neighbour.c:3879
 addrconf_sysctl_unregister net/ipv6/addrconf.c:7251 [inline]
 addrconf_ifdown+0x168b/0x1950 net/ipv6/addrconf.c:3977
 addrconf_notify+0x39f/0xe30 net/ipv6/addrconf.c:-1
 notifier_call_chain kernel/notifier.c:87 [inline]
 raw_notifier_call_chain+0xa1/0x110 kernel/notifier.c:455
 call_netdevice_notifiers_info net/core/dev.c:2022 [inline]
 call_netdevice_notifiers_extack net/core/dev.c:2060 [inline]
 call_netdevice_notifiers net/core/dev.c:2074 [inline]
 unregister_netdevice_many+0x104a/0x1910 net/core/dev.c:11005
 vti6_exit_batch_net+0x273/0x2c0 net/ipv6/ip6_vti.c:1203
 ops_exit_list net/core/net_namespace.c:177 [inline]
 cleanup_net+0x630/0xb10 net/core/net_namespace.c:604
 process_one_work+0x717/0xc30 kernel/workqueue.c:2302
 worker_thread+0xa4d/0x11d0 kernel/workqueue.c:2449
 kthread+0x281/0x320 kernel/kthread.c:386
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

The buggy address belongs to the object at ffff88813255d400
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 400 bytes inside of
 512-byte region [ffff88813255d400, ffff88813255d600)

The buggy address belongs to the physical page:
page:ffffea0004c95700 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x13255c
head:ffffea0004c95700 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head|zone=1)
raw: 4000000000010200 ffffea0004c99c00 dead000000000003 ffff888100042f00
raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 2, migratetype Unmovable, gfp_mask 0xd2a20(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 59, tgid 59 (kworker/1:2), ts 24731131262, free_ts 0
 set_page_owner include/linux/page_owner.h:33 [inline]
 post_alloc_hook+0x1f5/0x210 mm/page_alloc.c:2673
 prep_new_page+0x1c/0x110 mm/page_alloc.c:2680
 get_page_from_freelist+0x2ca9/0x2d20 mm/page_alloc.c:4587
 __alloc_pages+0x1fa/0x610 mm/page_alloc.c:5931
 alloc_slab_page+0x6e/0xf0 include/linux/gfp.h:-1
 allocate_slab mm/slub.c:1967 [inline]
 new_slab+0x98/0x3e0 mm/slub.c:2020
 ___slab_alloc+0x70f/0xb70 mm/slub.c:3177
 __slab_alloc+0x5e/0xa0 mm/slub.c:3263
 slab_alloc_node mm/slub.c:3348 [inline]
 __kmem_cache_alloc_node+0x204/0x2d0 mm/slub.c:3423
 __do_kmalloc_node mm/slab_common.c:937 [inline]
 __kmalloc_node_track_caller+0xa1/0x1e0 mm/slab_common.c:958
 kmalloc_reserve net/core/skbuff.c:449 [inline]
 __alloc_skb+0x226/0x4a0 net/core/skbuff.c:518
 alloc_skb include/linux/skbuff.h:1322 [inline]
 nlmsg_new include/net/netlink.h:987 [inline]
 inet6_ifa_notify net/ipv6/addrconf.c:5569 [inline]
 __ipv6_ifa_notify+0x200/0xe80 net/ipv6/addrconf.c:6227
 ipv6_ifa_notify net/ipv6/addrconf.c:6279 [inline]
 addrconf_dad_completed+0x192/0xe80 net/ipv6/addrconf.c:4283
 addrconf_dad_work+0xc1b/0x14a0 net/ipv6/addrconf.c:-1
 process_one_work+0x717/0xc30 kernel/workqueue.c:2302
 worker_thread+0xa4d/0x11d0 kernel/workqueue.c:2449
page_owner free stack trace missing

Memory state around the buggy address:
 ffff88813255d480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88813255d500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88813255d580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                         ^
 ffff88813255d600: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88813255d680: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================
----------------
Code disassembly (best guess):
   0:	48 89 47 18          	mov    %rax,0x18(%rdi)
   4:	48 89 47 20          	mov    %rax,0x20(%rdi)
   8:	48 89 47 28          	mov    %rax,0x28(%rdi)
   c:	48 89 47 30          	mov    %rax,0x30(%rdi)
  10:	48 89 47 38          	mov    %rax,0x38(%rdi)
  14:	48 8d 7f 40          	lea    0x40(%rdi),%rdi
  18:	75 d9                	jne    0xfffffff3
  1a:	90                   	nop
  1b:	c3                   	ret
  1c:	90                   	nop
  1d:	90                   	nop
  1e:	90                   	nop
  1f:	90                   	nop
  20:	90                   	nop
  21:	90                   	nop
  22:	90                   	nop
  23:	b9 00 10 00 00       	mov    $0x1000,%ecx
  28:	31 c0                	xor    %eax,%eax
* 2a:	f3 aa                	rep stos %al,%es:(%rdi) <-- trapping instruction
  2c:	c3                   	ret
  2d:	90                   	nop
  2e:	90                   	nop
  2f:	90                   	nop
  30:	90                   	nop
  31:	90                   	nop
  32:	90                   	nop
  33:	89 c8                	mov    %ecx,%eax
  35:	48 c1 e9 03          	shr    $0x3,%rcx
  39:	74 18                	je     0x53
  3b:	0f                   	.byte 0xf
  3c:	1f                   	(bad)
  3d:	84 00                	test   %al,(%rax)