==================================================================
BUG: KASAN: slab-use-after-free in __hlist_del include/linux/list.h:992 [inline]
BUG: KASAN: slab-use-after-free in hlist_del_init_rcu include/linux/rculist.h:238 [inline]
BUG: KASAN: slab-use-after-free in ipv6_del_acaddr_hash net/ipv6/anycast.c:254 [inline]
BUG: KASAN: slab-use-after-free in __ipv6_dev_ac_dec+0x4c2/0x690 net/ipv6/anycast.c:419
Write of size 8 at addr ffff8880227da420 by task syz.0.4580/20671

CPU: 1 UID: 0 PID: 20671 Comm: syz.0.4580 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description+0x55/0x1e0 mm/kasan/report.c:378
 print_report+0x58/0x70 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 __hlist_del include/linux/list.h:992 [inline]
 hlist_del_init_rcu include/linux/rculist.h:238 [inline]
 ipv6_del_acaddr_hash net/ipv6/anycast.c:254 [inline]
 __ipv6_dev_ac_dec+0x4c2/0x690 net/ipv6/anycast.c:419
 ipv6_dev_ac_dec net/ipv6/anycast.c:438 [inline]
 __ipv6_sock_ac_close+0x24e/0x430 net/ipv6/anycast.c:224
 inet6_release+0x4f/0x70 net/ipv6/af_inet6.c:470
 __sock_release net/socket.c:722 [inline]
 sock_close+0xc3/0x240 net/socket.c:1514
 __fput+0x44f/0xa60 fs/file_table.c:510
 task_work_run+0x1d9/0x270 kernel/task_work.c:233
 exit_task_work include/linux/task_work.h:40 [inline]
 do_exit+0x70f/0x22c0 kernel/exit.c:975
 do_group_exit+0x21b/0x2d0 kernel/exit.c:1117
 get_signal+0x1284/0x1330 kernel/signal.c:3037
 arch_do_signal_or_restart+0xbc/0x830 arch/x86/kernel/signal.c:337
 __exit_to_user_mode_loop kernel/entry/common.c:64 [inline]
 exit_to_user_mode_loop+0x86/0x480 kernel/entry/common.c:98
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:238 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:318 [inline]
 do_syscall_64+0x33e/0xf80 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f234d79cdd9
Code: Unable to access opcode bytes at 0x7f234d79cdaf.
RSP: 002b:00007f234e69b028 EFLAGS: 00000246 ORIG_RAX: 000000000000012b
RAX: 0000000000010106 RBX: 00007f234da16090 RCX: 00007f234d79cdd9
RDX: 0000000000010106 RSI: 00002000000000c0 RDI: 0000000000000006
RBP: 00007f234d832d69 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000002 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f234da16128 R14: 00007f234da16090 R15: 00007f234db3fa48
 </TASK>

Allocated by task 20672:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __kmalloc_cache_noprof+0x31c/0x660 mm/slub.c:5419
 kmalloc_noprof include/linux/slab.h:950 [inline]
 kzalloc_noprof include/linux/slab.h:1188 [inline]
 aca_alloc net/ipv6/anycast.c:282 [inline]
 __ipv6_dev_ac_inc+0x37f/0xaf0 net/ipv6/anycast.c:360
 ipv6_sock_ac_join+0x6a8/0x880 net/ipv6/anycast.c:153
 do_ipv6_setsockopt+0x203a/0x3150 net/ipv6/ipv6_sockglue.c:893
 ipv6_setsockopt+0x59/0x170 net/ipv6/ipv6_sockglue.c:965
 do_sock_setsockopt+0x17c/0x1b0 net/socket.c:2381
 __sys_setsockopt net/socket.c:2406 [inline]
 __do_sys_setsockopt net/socket.c:2412 [inline]
 __se_sys_setsockopt net/socket.c:2409 [inline]
 __x64_sys_setsockopt+0x13d/0x1b0 net/socket.c:2409
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 23:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2689 [inline]
 slab_free mm/slub.c:6250 [inline]
 kfree+0x1c5/0x640 mm/slub.c:6565
 rcu_do_batch kernel/rcu/tree.c:2617 [inline]
 rcu_core+0x7cd/0x1070 kernel/rcu/tree.c:2869
 handle_softirqs+0x22a/0x840 kernel/softirq.c:622
 run_ksoftirqd+0x36/0x60 kernel/softirq.c:1076
 smpboot_thread_fn+0x541/0xa50 kernel/smpboot.c:160
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Last potentially related work creation:
 kasan_save_stack+0x3e/0x60 mm/kasan/common.c:57
 kasan_record_aux_stack+0xbd/0xd0 mm/kasan/generic.c:556
 __call_rcu_common kernel/rcu/tree.c:3131 [inline]
 call_rcu+0xee/0x890 kernel/rcu/tree.c:3251
 call_rcu_hurry include/linux/rcupdate.h:125 [inline]
 aca_put net/ipv6/anycast.c:274 [inline]
 __ipv6_dev_ac_inc+0x8e0/0xaf0 net/ipv6/anycast.c:384
 ipv6_sock_ac_join+0x6a8/0x880 net/ipv6/anycast.c:153
 do_ipv6_setsockopt+0x203a/0x3150 net/ipv6/ipv6_sockglue.c:893
 ipv6_setsockopt+0x59/0x170 net/ipv6/ipv6_sockglue.c:965
 do_sock_setsockopt+0x17c/0x1b0 net/socket.c:2381
 __sys_setsockopt net/socket.c:2406 [inline]
 __do_sys_setsockopt net/socket.c:2412 [inline]
 __se_sys_setsockopt net/socket.c:2409 [inline]
 __x64_sys_setsockopt+0x13d/0x1b0 net/socket.c:2409
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff8880227da400
 which belongs to the cache kmalloc-96 of size 96
The buggy address is located 32 bytes inside of
 freed 96-byte region [ffff8880227da400, ffff8880227da460)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x227da
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000000 ffff88813fe19280 dead000000000100 dead000000000122
raw: 0000000000000000 0000000800200020 00000000f5000000 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0xd2820(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 57, tgid 57 (kworker/u8:4), ts 95690583368, free_ts 95636416997
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x231/0x280 mm/page_alloc.c:1858
 prep_new_page mm/page_alloc.c:1866 [inline]
 get_page_from_freelist+0x24ba/0x2540 mm/page_alloc.c:3946
 __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5226
 alloc_slab_page mm/slub.c:3278 [inline]
 allocate_slab+0x77/0x660 mm/slub.c:3467
 new_slab mm/slub.c:3525 [inline]
 refill_objects+0x339/0x3d0 mm/slub.c:7255
 refill_sheaf mm/slub.c:2816 [inline]
 __pcs_replace_empty_main+0x321/0x720 mm/slub.c:4651
 alloc_from_pcs mm/slub.c:4749 [inline]
 slab_alloc_node mm/slub.c:4883 [inline]
 __kmalloc_cache_noprof+0x392/0x660 mm/slub.c:5414
 kmalloc_noprof include/linux/slab.h:950 [inline]
 dst_cow_metrics_generic+0x56/0x1c0 net/core/dst.c:194
 dst_metrics_write_ptr include/net/dst.h:136 [inline]
 dst_metric_set include/net/dst.h:197 [inline]
 icmp6_dst_alloc+0x265/0x440 net/ipv6/route.c:3350
 mld_sendpack+0x6ba/0xe40 net/ipv6/mcast.c:1844
 ipv6_mc_dad_complete+0x88/0x540 net/ipv6/mcast.c:2279
 addrconf_dad_completed+0x8a7/0xe60 net/ipv6/addrconf.c:4352
 addrconf_dad_work+0xc5e/0x14c0 net/ipv6/addrconf.c:-1
 process_one_work kernel/workqueue.c:3302 [inline]
 process_scheduled_works+0xb5d/0x1860 kernel/workqueue.c:3385
 worker_thread+0xa53/0xfc0 kernel/workqueue.c:3466
 kthread+0x388/0x470 kernel/kthread.c:436
page last free pid 5647 tgid 5647 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 __free_pages_prepare mm/page_alloc.c:1402 [inline]
 __free_frozen_pages+0xbc7/0xd30 mm/page_alloc.c:2943
 __tlb_remove_table_free mm/mmu_gather.c:228 [inline]
 tlb_remove_table_rcu+0x85/0x100 mm/mmu_gather.c:291
 rcu_do_batch kernel/rcu/tree.c:2617 [inline]
 rcu_core+0x7cd/0x1070 kernel/rcu/tree.c:2869
 handle_softirqs+0x22a/0x840 kernel/softirq.c:622
 __do_softirq kernel/softirq.c:656 [inline]
 invoke_softirq kernel/softirq.c:496 [inline]
 __irq_exit_rcu+0xca/0x220 kernel/softirq.c:735
 irq_exit_rcu+0x9/0x30 kernel/softirq.c:752
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1061 [inline]
 sysvec_apic_timer_interrupt+0xa6/0xc0 arch/x86/kernel/apic/apic.c:1061
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697

Memory state around the buggy address:
 ffff8880227da300: 00 00 00 00 00 00 00 00 00 00 fc fc fc fc fc fc
 ffff8880227da380: fa fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
>ffff8880227da400: fa fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
                               ^
 ffff8880227da480: fa fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
 ffff8880227da500: fa fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
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