================================================================== BUG: KASAN: use-after-free in rcu_cblist_dequeue+0x6c/0xb0 kernel/rcu/rcu_segcblist.c:75 Read of size 8 at addr ffff888115b3a990 by task syz.7.749/3056 CPU: 1 PID: 3056 Comm: syz.7.749 Not tainted syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026 Call Trace: __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 kernel/softirq.c:621 [inline] invoke_softirq kernel/softirq.c:443 [inline] __irq_exit_rcu+0x52/0xf0 kernel/softirq.c:670 irq_exit_rcu+0x9/0x10 kernel/softirq.c:682 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1108 [inline] sysvec_apic_timer_interrupt+0xa9/0xc0 arch/x86/kernel/apic/apic.c:1108 asm_sysvec_apic_timer_interrupt+0x1b/0x20 arch/x86/include/asm/idtentry.h:676 RIP: 0010:PageAnon include/linux/page-flags.h:511 [inline] RIP: 0010:mm_counter include/linux/mm.h:2044 [inline] RIP: 0010:zap_pte_range mm/memory.c:1450 [inline] RIP: 0010:zap_pmd_range mm/memory.c:1577 [inline] RIP: 0010:zap_pud_range mm/memory.c:1606 [inline] RIP: 0010:zap_p4d_range mm/memory.c:1627 [inline] RIP: 0010:unmap_page_range+0xea6/0x1e00 mm/memory.c:1648 Code: 0f 85 72 06 00 00 e8 c9 48 cb ff 4c 8b 74 24 10 49 83 c6 18 4c 89 f0 48 c1 e8 03 42 80 3c 20 00 74 08 4c 89 f7 e8 5a ba 0a 00 <4d> 8b 36 4c 89 f6 48 83 e6 01 31 ff e8 d9 4c cb ff 49 83 e6 01 75 RSP: 0018:ffffc90000b275a0 EFLAGS: 00000246 RAX: 1ffffd4000939543 RBX: ffff888142eb8988 RCX: ffff8881083cbb40 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000 RBP: ffffc90000b27770 R08: ffff8881083cbb47 R09: 1ffff11021079768 R10: dffffc0000000000 R11: ffffed1021079769 R12: dffffc0000000000 R13: ffffea00049caa08 R14: ffffea00049caa18 R15: 1ffffd4000939541 unmap_single_vma mm/memory.c:1693 [inline] unmap_vmas+0x26d/0x380 mm/memory.c:1725 exit_mmap+0x412/0x8b0 mm/mmap.c:3245 __mmput+0x92/0x300 kernel/fork.c:1185 mmput+0x50/0x150 kernel/fork.c:1208 exit_mm kernel/exit.c:555 [inline] do_exit+0xacc/0x29a0 kernel/exit.c:877 do_group_exit+0x149/0x310 kernel/exit.c:1004 get_signal+0x64f/0x1430 kernel/signal.c:2908 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 RIP: 0033:0x7ff584ad7e99 Code: Unable to access opcode bytes at RIP 0x7ff584ad7e6f. RSP: 002b:00007ff5835310e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca RAX: fffffffffffffe00 RBX: 00007ff584d5ffa8 RCX: 00007ff584ad7e99 RDX: 0000000000000000 RSI: 0000000000000080 RDI: 00007ff584d5ffa8 RBP: 00007ff584d5ffa0 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007ff584d60038 R14: 00007ffed7b16730 R15: 00007ffed7b16818 Allocated by task 3058: 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 1784: 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 tracehook_notify_resume include/linux/tracehook.h:189 [inline] exit_to_user_mode_loop+0xd0/0xe0 kernel/entry/common.c:181 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 The buggy address belongs to the object at ffff888115b3a800 which belongs to the cache kmalloc-512 of size 512 The buggy address is located 400 bytes inside of 512-byte region [ffff888115b3a800, ffff888115b3aa00) The buggy address belongs to the page: page:ffffea000456ce00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x115b38 head:ffffea000456ce00 order:2 compound_mapcount:0 compound_pincount:0 flags: 0x4000000000010200(slab|head|zone=1) raw: 4000000000010200 ffffea00049c8a00 0000000700000007 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 105, ts 5886090785, free_ts 0 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_track_caller+0x169/0x2c0 mm/slub.c:4954 kmalloc_reserve net/core/skbuff.c:357 [inline] __alloc_skb+0x210/0x730 net/core/skbuff.c:428 alloc_skb include/linux/skbuff.h:1183 [inline] alloc_skb_with_frags+0xa8/0x620 net/core/skbuff.c:6207 sock_alloc_send_pskb+0x87f/0x9a0 net/core/sock.c:2542 unix_dgram_sendmsg+0x6f3/0x19b0 net/unix/af_unix.c:1816 sock_sendmsg_nosec net/socket.c:704 [inline] __sock_sendmsg net/socket.c:716 [inline] sock_write_iter+0x2a6/0x3a0 net/socket.c:1080 call_write_iter include/linux/fs.h:2212 [inline] new_sync_write fs/read_write.c:507 [inline] vfs_write+0x831/0xfd0 fs/read_write.c:594 ksys_write+0x14a/0x260 fs/read_write.c:647 __do_sys_write fs/read_write.c:659 [inline] __se_sys_write fs/read_write.c:656 [inline] __x64_sys_write+0x7b/0x90 fs/read_write.c:656 page_owner free stack trace missing Memory state around the buggy address: ffff888115b3a880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff888115b3a900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >ffff888115b3a980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff888115b3aa00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ffff888115b3aa80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ================================================================== ---------------- Code disassembly (best guess): 0: 0f 85 72 06 00 00 jne 0x678 6: e8 c9 48 cb ff call 0xffcb48d4 b: 4c 8b 74 24 10 mov 0x10(%rsp),%r14 10: 49 83 c6 18 add $0x18,%r14 14: 4c 89 f0 mov %r14,%rax 17: 48 c1 e8 03 shr $0x3,%rax 1b: 42 80 3c 20 00 cmpb $0x0,(%rax,%r12,1) 20: 74 08 je 0x2a 22: 4c 89 f7 mov %r14,%rdi 25: e8 5a ba 0a 00 call 0xaba84 * 2a: 4d 8b 36 mov (%r14),%r14 <-- trapping instruction 2d: 4c 89 f6 mov %r14,%rsi 30: 48 83 e6 01 and $0x1,%rsi 34: 31 ff xor %edi,%edi 36: e8 d9 4c cb ff call 0xffcb4d14 3b: 49 83 e6 01 and $0x1,%r14 3f: 75 .byte 0x75