==================================================================
BUG: KASAN: use-after-free in rcu_cblist_dequeue+0x6c/0xb0 kernel/rcu/rcu_segcblist.c:75
Read of size 8 at addr ffff88811cb5fd90 by task syz.1.76/557

CPU: 0 PID: 557 Comm: syz.1.76 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/07/2026
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+0x1dd/0x5f0 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:check_region_inline mm/kasan/generic.c:-1 [inline]
RIP: 0010:kasan_check_range+0x13/0x2a0 mm/kasan/generic.c:189
Code: 00 00 cc cc 00 00 cc 90 90 90 90 90 90 90 90 90 90 90 b8 bf f3 05 3b b0 01 48 85 f6 0f 84 c0 01 00 00 55 48 89 e5 41 57 41 56 <41> 55 41 54 53 49 89 f8 49 01 f0 0f 82 1d 02 00 00 49 89 f8 49 c1
RSP: 0018:ffffc90001217a90 EFLAGS: 00000202
RAX: 1ffff11023c53e01 RBX: ffffea00049425e8 RCX: ffffffff85020ea4
RDX: 0000000000000001 RSI: 0000000000000004 RDI: ffffc90001217ae0
RBP: ffffc90001217aa0 R08: ffffea00049425eb R09: 1ffffd40009284bd
R10: dffffc0000000000 R11: fffff940009284be R12: dffffc0000000000
R13: ffff88811e557301 R14: ffffc90001217ae0 R15: 1ffff92000242f58
 __kasan_check_write+0x14/0x20 mm/kasan/shadow.c:37
 instrument_atomic_read_write include/linux/instrumented.h:102 [inline]
 atomic_try_cmpxchg_acquire include/linux/atomic/atomic-instrumented.h:542 [inline]
 queued_spin_lock include/asm-generic/qspinlock.h:111 [inline]
 do_raw_spin_lock include/linux/spinlock.h:187 [inline]
 __raw_spin_lock include/linux/spinlock_api_smp.h:134 [inline]
 _raw_spin_lock+0x94/0xf0 kernel/locking/spinlock.c:154
 spin_lock include/linux/spinlock.h:351 [inline]
 follow_page_pte+0x302/0xb60 mm/gup.c:573
 follow_pmd_mask mm/gup.c:-1 [inline]
 follow_pud_mask mm/gup.c:827 [inline]
 follow_p4d_mask mm/gup.c:853 [inline]
 follow_page_mask+0x77b/0xef0 mm/gup.c:917
 __get_user_pages+0x2e7/0xdb0 mm/gup.c:1248
 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]
 __do_sys_mlockall mm/mlock.c:724 [inline]
 __se_sys_mlockall+0x397/0x450 mm/mlock.c:700
 __x64_sys_mlockall+0x38/0x40 mm/mlock.c:700
 x64_sys_call+0x289/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:152
 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: 0033:0x7f6ef979f559
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:00007f6efa5de028 EFLAGS: 00000246 ORIG_RAX: 0000000000000097
RAX: ffffffffffffffda RBX: 00007f6ef9a25fa0 RCX: 00007f6ef979f559
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000001
RBP: 00007f6ef9836b20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f6ef9a26038 R14: 00007f6ef9a25fa0 R15: 00007ffd34436738
 </TASK>

Allocated by task 546:
 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 8:
 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

The buggy address belongs to the object at ffff88811cb5fc00
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 400 bytes inside of
 512-byte region [ffff88811cb5fc00, ffff88811cb5fe00)

The buggy address belongs to the physical page:
page:ffffea000472d700 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x11cb5c
head:ffffea000472d700 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head|zone=1)
raw: 4000000000010200 ffffea00046d1f00 dead000000000002 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 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 113, tgid 113 (udevd), ts 5227554648, 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]
 alloc_skb_with_frags+0xa8/0x620 net/core/skbuff.c:6189
 sock_alloc_send_pskb+0x87f/0x9a0 net/core/sock.c:2770
 unix_dgram_sendmsg+0x5c1/0x1710 net/unix/af_unix.c:1959
 sock_sendmsg_nosec net/socket.c:716 [inline]
 __sock_sendmsg net/socket.c:728 [inline]
 sock_write_iter+0x2ea/0x3f0 net/socket.c:1134
 call_write_iter include/linux/fs.h:2282 [inline]
 new_sync_write fs/read_write.c:491 [inline]
 vfs_write+0x5ef/0xd00 fs/read_write.c:584
page_owner free stack trace missing

Memory state around the buggy address:
 ffff88811cb5fc80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88811cb5fd00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88811cb5fd80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                         ^
 ffff88811cb5fe00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88811cb5fe80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================
page_owner tracks the page as allocated
page last allocated via order 2, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 113, tgid 113 (udevd), ts 5227554648, free_ts 0
page_owner free stack trace missing
----------------
Code disassembly (best guess):
   0:	00 00                	add    %al,(%rax)
   2:	cc                   	int3
   3:	cc                   	int3
   4:	00 00                	add    %al,(%rax)
   6:	cc                   	int3
   7:	90                   	nop
   8:	90                   	nop
   9:	90                   	nop
   a:	90                   	nop
   b:	90                   	nop
   c:	90                   	nop
   d:	90                   	nop
   e:	90                   	nop
   f:	90                   	nop
  10:	90                   	nop
  11:	90                   	nop
  12:	b8 bf f3 05 3b       	mov    $0x3b05f3bf,%eax
  17:	b0 01                	mov    $0x1,%al
  19:	48 85 f6             	test   %rsi,%rsi
  1c:	0f 84 c0 01 00 00    	je     0x1e2
  22:	55                   	push   %rbp
  23:	48 89 e5             	mov    %rsp,%rbp
  26:	41 57                	push   %r15
  28:	41 56                	push   %r14
* 2a:	41 55                	push   %r13 <-- trapping instruction
  2c:	41 54                	push   %r12
  2e:	53                   	push   %rbx
  2f:	49 89 f8             	mov    %rdi,%r8
  32:	49 01 f0             	add    %rsi,%r8
  35:	0f 82 1d 02 00 00    	jb     0x258
  3b:	49 89 f8             	mov    %rdi,%r8
  3e:	49                   	rex.WB
  3f:	c1                   	.byte 0xc1