==================================================================
BUG: KASAN: use-after-free in rcu_cblist_dequeue+0x6c/0xb0 kernel/rcu/rcu_segcblist.c:75
Read of size 8 at addr ffff888128ada190 by task syz.8.1089/4754

CPU: 0 PID: 4754 Comm: syz.8.1089 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
 <IRQ>
 __dump_stack+0x21/0x30 lib/dump_stack.c:88
 dump_stack_lvl+0x110/0x170 lib/dump_stack.c:106
 print_address_description+0x7f/0x2c0 mm/kasan/report.c:248
 __kasan_report mm/kasan/report.c:427 [inline]
 kasan_report+0x10f/0x150 mm/kasan/report.c:444
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report_generic.c:309
 rcu_cblist_dequeue+0x6c/0xb0 kernel/rcu/rcu_segcblist.c:75
 rcu_do_batch+0x47d/0xbf0 kernel/rcu/tree.c:2512
 rcu_core+0x4a3/0xef0 kernel/rcu/tree.c:2763
 rcu_core_si+0x9/0x10 kernel/rcu/tree.c:2776
 handle_softirqs+0x250/0x560 kernel/softirq.c:583
 __do_softirq+0xb/0xd kernel/softirq.c:621
 do_softirq+0xdc/0x130 kernel/softirq.c:470
 </IRQ>
 <TASK>
 __local_bh_enable_ip+0x75/0x80 kernel/softirq.c:397
 local_bh_enable+0x1f/0x30 include/linux/bottom_half.h:32
 rcu_read_unlock_bh include/linux/rcupdate.h:819 [inline]
 ip_finish_output2+0xb8d/0xec0 net/ipv4/ip_output.c:229
 __ip_finish_output+0x163/0x360 net/ipv4/ip_output.c:-1
 ip_finish_output+0x31/0x220 net/ipv4/ip_output.c:316
 NF_HOOK_COND include/linux/netfilter.h:294 [inline]
 ip_output+0x1ea/0x390 net/ipv4/ip_output.c:434
 dst_output include/net/dst.h:453 [inline]
 ip_local_out net/ipv4/ip_output.c:126 [inline]
 ip_send_skb net/ipv4/ip_output.c:1590 [inline]
 ip_push_pending_frames+0x2c9/0x570 net/ipv4/ip_output.c:1610
 raw_sendmsg+0xe73/0x13f0 net/ipv4/raw.c:679
 inet_sendmsg+0xa5/0xc0 net/ipv4/af_inet.c:830
 sock_sendmsg_nosec net/socket.c:704 [inline]
 __sock_sendmsg net/socket.c:716 [inline]
 ____sys_sendmsg+0x5be/0x8f0 net/socket.c:2436
 ___sys_sendmsg+0x236/0x2e0 net/socket.c:2490
 __sys_sendmmsg+0x2ba/0x4e0 net/socket.c:2576
 __do_sys_sendmmsg net/socket.c:2605 [inline]
 __se_sys_sendmmsg net/socket.c:2602 [inline]
 __x64_sys_sendmmsg+0xa0/0xb0 net/socket.c:2602
 x64_sys_call+0x6c6/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:308
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f312acc4159
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:00007f31296db028 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: ffffffffffffffda RBX: 00007f312af4c180 RCX: 00007f312acc4159
RDX: 0000000004000095 RSI: 0000200000005240 RDI: 0000000000000009
RBP: 00007f312ad5b06b R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000a00 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f312af4c218 R14: 00007f312af4c180 R15: 00007ffd873c42e8
 </TASK>

Allocated by task 4759:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track mm/kasan/common.c:45 [inline]
 set_alloc_info mm/kasan/common.c:433 [inline]
 ____kasan_kmalloc mm/kasan/common.c:512 [inline]
 __kasan_kmalloc+0xd4/0x100 mm/kasan/common.c:521
 kasan_kmalloc include/linux/kasan.h:227 [inline]
 __kmalloc+0x13d/0x2c0 mm/slub.c:4436
 kmalloc include/linux/slab.h:624 [inline]
 kzalloc include/linux/slab.h:750 [inline]
 l2tp_session_create+0x39/0xb60 net/l2tp/l2tp_core.c:1616
 pppol2tp_connect+0xbf5/0x1640 net/l2tp/l2tp_ppp.c:772
 __sys_connect_file net/socket.c:1923 [inline]
 __sys_connect+0x3cb/0x450 net/socket.c:1940
 __do_sys_connect net/socket.c:1950 [inline]
 __se_sys_connect net/socket.c:1947 [inline]
 __x64_sys_connect+0x7a/0x90 net/socket.c:1947
 x64_sys_call+0x7c/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:43
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0

Freed by task 421:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track+0x4a/0x70 mm/kasan/common.c:45
 kasan_set_free_info+0x23/0x40 mm/kasan/generic.c:370
 ____kasan_slab_free+0x125/0x160 mm/kasan/common.c:365
 __kasan_slab_free+0x11/0x20 mm/kasan/common.c:373
 kasan_slab_free include/linux/kasan.h:193 [inline]
 slab_free_hook mm/slub.c:1728 [inline]
 slab_free_freelist_hook+0xc2/0x190 mm/slub.c:1754
 slab_free mm/slub.c:3526 [inline]
 kfree+0xc4/0x270 mm/slub.c:4588
 l2tp_session_free net/l2tp/l2tp_core.c:168 [inline]
 l2tp_session_put+0xaf/0x1a0 net/l2tp/l2tp_core.c:193
 l2tp_session_delete+0x3a9/0x4a0 net/l2tp/l2tp_core.c:1589
 l2tp_tunnel_closeall net/l2tp/l2tp_core.c:1235 [inline]
 l2tp_tunnel_del_work+0x180/0x3d0 net/l2tp/l2tp_core.c:1273
 process_one_work+0x6c8/0xbb0 kernel/workqueue.c:2328
 worker_thread+0xaa0/0x1250 kernel/workqueue.c:2475
 kthread+0x3f5/0x4f0 kernel/kthread.c:337
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287

Last potentially related work creation:
 kasan_save_stack+0x3a/0x60 mm/kasan/common.c:38
 __kasan_record_aux_stack+0xd2/0x100 mm/kasan/generic.c:348
 kasan_record_aux_stack_noalloc+0xb/0x10 mm/kasan/generic.c:358
 __call_rcu_common kernel/rcu/tree.c:3011 [inline]
 call_rcu+0x10b/0xf60 kernel/rcu/tree.c:3129
 pppol2tp_release+0x1e3/0x2b0 net/l2tp/l2tp_ppp.c:447
 __sock_release net/socket.c:649 [inline]
 sock_close+0xb8/0x200 net/socket.c:1336
 __fput+0x22b/0x900 fs/file_table.c:311
 ____fput+0x15/0x20 fs/file_table.c:339
 task_work_run+0x127/0x190 kernel/task_work.c:188
 exit_task_work include/linux/task_work.h:33 [inline]
 do_exit+0xb70/0x29a0 kernel/exit.c:896
 do_group_exit+0x149/0x310 kernel/exit.c:1010
 get_signal+0x64f/0x1430 kernel/signal.c:2916
 arch_do_signal_or_restart+0xe2/0x1100 arch/x86/kernel/signal.c:867
 handle_signal_work kernel/entry/common.c:154 [inline]
 exit_to_user_mode_loop+0xa7/0xe0 kernel/entry/common.c:178
 exit_to_user_mode_prepare+0x87/0xd0 kernel/entry/common.c:214
 __syscall_exit_to_user_mode_work kernel/entry/common.c:296 [inline]
 syscall_exit_to_user_mode+0x1a/0x30 kernel/entry/common.c:307
 do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x66/0xd0

Second to last potentially related work creation:
 kasan_save_stack+0x3a/0x60 mm/kasan/common.c:38
 __kasan_record_aux_stack+0xd2/0x100 mm/kasan/generic.c:348
 kasan_record_aux_stack_noalloc+0xb/0x10 mm/kasan/generic.c:358
 __call_rcu_common kernel/rcu/tree.c:3011 [inline]
 call_rcu+0x10b/0xf60 kernel/rcu/tree.c:3129
 fib6_info_release include/net/ip6_fib.h:349 [inline]
 fib6_del_route net/ipv6/ip6_fib.c:1998 [inline]
 fib6_del+0xbf0/0xf00 net/ipv6/ip6_fib.c:2031
 fib6_clean_node+0x2a1/0x540 net/ipv6/ip6_fib.c:2193
 fib6_walk_continue+0x54b/0x740 net/ipv6/ip6_fib.c:2115
 fib6_walk+0x153/0x290 net/ipv6/ip6_fib.c:2163
 fib6_clean_tree net/ipv6/ip6_fib.c:2243 [inline]
 __fib6_clean_all net/ipv6/ip6_fib.c:2259 [inline]
 fib6_clean_all+0x1a1/0x270 net/ipv6/ip6_fib.c:2270
 rt6_sync_down_dev net/ipv6/route.c:4906 [inline]
 rt6_disable_ip+0x12a/0x840 net/ipv6/route.c:4911
 addrconf_ifdown+0x144/0x1910 net/ipv6/addrconf.c:3809
 addrconf_notify+0x3bd/0xe00 net/ipv6/addrconf.c:-1
 notifier_call_chain kernel/notifier.c:83 [inline]
 raw_notifier_call_chain+0x90/0x100 kernel/notifier.c:391
 call_netdevice_notifiers_info net/core/dev.c:2070 [inline]
 call_netdevice_notifiers_extack net/core/dev.c:2082 [inline]
 call_netdevice_notifiers net/core/dev.c:2096 [inline]
 dev_close_many+0x325/0x4d0 net/core/dev.c:1671
 unregister_netdevice_many+0x477/0x1a00 net/core/dev.c:11152
 ip_tunnel_delete_nets+0x343/0x390 net/ipv4/ip_tunnel.c:1123
 vti_exit_batch_net+0x22/0x30 net/ipv4/ip_vti.c:515
 ops_exit_list net/core/net_namespace.c:177 [inline]
 cleanup_net+0x605/0xae0 net/core/net_namespace.c:599
 process_one_work+0x6c8/0xbb0 kernel/workqueue.c:2328
 worker_thread+0xaa0/0x1250 kernel/workqueue.c:2475
 kthread+0x3f5/0x4f0 kernel/kthread.c:337
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287

The buggy address belongs to the object at ffff888128ada000
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 400 bytes inside of
 512-byte region [ffff888128ada000, ffff888128ada200)
The buggy address belongs to the page:
page:ffffea0004a2b600 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x128ad8
head:ffffea0004a2b600 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head|zone=1)
raw: 4000000000010200 ffffea0004a26900 0000000600000005 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 0x1d20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 2409, ts 127862147707, free_ts 127810164803
 set_page_owner include/linux/page_owner.h:33 [inline]
 post_alloc_hook+0x192/0x1b0 mm/page_alloc.c:2607
 prep_new_page+0x1c/0x110 mm/page_alloc.c:2613
 get_page_from_freelist+0x2c3a/0x2cd0 mm/page_alloc.c:4487
 __alloc_pages+0x1a2/0x460 mm/page_alloc.c:5824
 alloc_slab_page mm/slub.c:-1 [inline]
 allocate_slab mm/slub.c:1937 [inline]
 new_slab+0xa0/0x4d0 mm/slub.c:2000
 ___slab_alloc+0x3ac/0x840 mm/slub.c:3033
 __slab_alloc+0x49/0x90 mm/slub.c:3120
 slab_alloc_node mm/slub.c:3211 [inline]
 slab_alloc mm/slub.c:3255 [inline]
 __kmalloc+0x16a/0x2c0 mm/slub.c:4432
 kmalloc include/linux/slab.h:624 [inline]
 kzalloc include/linux/slab.h:750 [inline]
 fib6_info_alloc+0x34/0xe0 net/ipv6/ip6_fib.c:155
 ip6_route_info_create+0x51b/0x14d0 net/ipv6/route.c:3783
 ip6_route_add+0x27/0x130 net/ipv6/route.c:3879
 addrconf_add_mroute net/ipv6/addrconf.c:2542 [inline]
 addrconf_add_dev+0x385/0x4c0 net/ipv6/addrconf.c:2560
 inet6_addr_add+0x1a6/0x9d0 net/ipv6/addrconf.c:3000
 inet6_rtm_newaddr+0x6e7/0x9c0 net/ipv6/addrconf.c:4985
 rtnetlink_rcv_msg+0x9fd/0xcb0 net/core/rtnetlink.c:5662
 netlink_rcv_skb+0x1e9/0x430 net/netlink/af_netlink.c:2520
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:26 [inline]
 free_pages_prepare mm/page_alloc.c:1474 [inline]
 free_pcp_prepare mm/page_alloc.c:1546 [inline]
 free_unref_page_prepare+0x5fa/0x600 mm/page_alloc.c:3536
 free_unref_page_list+0x138/0x9e0 mm/page_alloc.c:3673
 release_pages+0x1264/0x12c0 mm/swap.c:1015
 free_pages_and_swap_cache+0x86/0xa0 mm/swap_state.c:320
 tlb_batch_pages_flush mm/mmu_gather.c:49 [inline]
 tlb_flush_mmu_free mm/mmu_gather.c:240 [inline]
 tlb_flush_mmu mm/mmu_gather.c:247 [inline]
 tlb_finish_mmu+0x17e/0x310 mm/mmu_gather.c:338
 exit_mmap+0x43b/0x8b0 mm/mmap.c:3248
 __mmput+0x92/0x300 kernel/fork.c:1191
 mmput+0x50/0x150 kernel/fork.c:1214
 exit_mm kernel/exit.c:561 [inline]
 do_exit+0xacc/0x29a0 kernel/exit.c:883
 do_group_exit+0x149/0x310 kernel/exit.c:1010
 get_signal+0x64f/0x1430 kernel/signal.c:2916
 arch_do_signal_or_restart+0xe2/0x1100 arch/x86/kernel/signal.c:867
 handle_signal_work kernel/entry/common.c:154 [inline]
 exit_to_user_mode_loop+0xa7/0xe0 kernel/entry/common.c:178
 exit_to_user_mode_prepare+0x87/0xd0 kernel/entry/common.c:214
 __syscall_exit_to_user_mode_work kernel/entry/common.c:296 [inline]
 syscall_exit_to_user_mode+0x1a/0x30 kernel/entry/common.c:307
 do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86

Memory state around the buggy address:
 ffff888128ada080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888128ada100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888128ada180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                         ^
 ffff888128ada200: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888128ada280: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================