================================================================== BUG: KASAN: use-after-free in rcu_cblist_dequeue+0x6c/0xb0 kernel/rcu/rcu_segcblist.c:75 Read of size 8 at addr ffff888125fead90 by task syz.4.2341/7506 CPU: 0 PID: 7506 Comm: syz.4.2341 Tainted: G W syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026 Call Trace: __dump_stack+0x21/0x24 lib/dump_stack.c:77 dump_stack_lvl+0x1a7/0x208 lib/dump_stack.c:118 print_address_description+0x7f/0x2c0 mm/kasan/report.c:248 __kasan_report mm/kasan/report.c:435 [inline] kasan_report+0x100/0x140 mm/kasan/report.c:452 __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+0x448/0xaf0 kernel/rcu/tree.c:2484 rcu_core+0x50a/0xca0 kernel/rcu/tree.c:2735 rcu_core_si+0x9/0x10 kernel/rcu/tree.c:2748 __do_softirq+0x255/0x563 kernel/softirq.c:309 asm_call_irq_on_stack+0xf/0x20 __run_on_irqstack arch/x86/include/asm/irq_stack.h:26 [inline] run_on_irqstack_cond arch/x86/include/asm/irq_stack.h:77 [inline] do_softirq_own_stack+0x60/0x80 arch/x86/kernel/irq_64.c:77 invoke_softirq kernel/softirq.c:405 [inline] __irq_exit_rcu+0x128/0x150 kernel/softirq.c:435 irq_exit_rcu+0x9/0x10 kernel/softirq.c:447 sysvec_call_function_single+0xbc/0xd0 arch/x86/kernel/smp.c:243 asm_sysvec_call_function_single+0x12/0x20 arch/x86/include/asm/idtentry.h:643 RIP: 0010:exit_to_user_mode_loop+0x44/0xe0 kernel/entry/common.c:159 Code: eb 23 e8 8f 0b 4e 00 e8 2a 26 e1 00 fa 65 48 8b 05 c1 38 ae 7e 4c 8b 30 41 f7 c6 0e 30 08 00 0f 84 91 00 00 00 fb 41 f6 c6 08 <74> 05 e8 65 61 2c 03 41 f7 c6 00 10 00 00 74 08 48 89 df e8 14 49 RSP: 0000:ffffc90001367ed0 EFLAGS: 00000202 RAX: 0000000000000000 RBX: ffffc90001367f58 RCX: 74f122dc09d9ce00 RDX: 0000000000400140 RSI: 0000000000000308 RDI: ffffc90001367f58 RBP: ffffc90001367ee0 R08: ffffffff86e79008 R09: ffffffff86e79018 R10: ffffffff86e7901c R11: ffffffff86e79003 R12: ffffffff84a00c7a R13: 0000000000000000 R14: 0000000000000308 R15: 0000000000000000 exit_to_user_mode_prepare+0x76/0xa0 kernel/entry/common.c:199 irqentry_exit_to_user_mode+0x9/0x10 kernel/entry/common.c:287 irqentry_exit+0x12/0x60 kernel/entry/common.c:375 sysvec_apic_timer_interrupt+0xcb/0xe0 arch/x86/kernel/apic/apic.c:1106 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:635 RIP: 0033:0x7f7327d2a578 Code: 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 84 00 00 00 00 00 0f b7 03 83 c0 03 25 fc ff 01 00 48 01 c3 48 39 d3 73 35 66 83 7b 02 01 <75> e6 0f b7 5b 04 66 85 db 74 25 31 c9 ba 00 10 00 00 89 ef e8 bf RSP: 002b:00007f73268c0f50 EFLAGS: 00000297 RAX: 0000000000000000 RBX: 00007f73268c101c RCX: 0000000000000000 RDX: 00007f73268c1588 RSI: 00007f73268c1000 RDI: 0000000000000005 RBP: 0000000000000005 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00002000000000c0 R13: 00007f73268c0fb0 R14: 000000000000000c R15: 0000000000000000 Allocated by task 7517: 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:430 [inline] ____kasan_kmalloc mm/kasan/common.c:509 [inline] __kasan_kmalloc+0xd4/0x100 mm/kasan/common.c:518 kasan_kmalloc include/linux/kasan.h:254 [inline] __kmalloc+0x19f/0x330 mm/slub.c:4038 kmalloc include/linux/slab.h:560 [inline] kzalloc include/linux/slab.h:667 [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:1866 [inline] __sys_connect+0x3ce/0x450 net/socket.c:1883 __do_sys_connect net/socket.c:1893 [inline] __se_sys_connect net/socket.c:1890 [inline] __x64_sys_connect+0x7a/0x90 net/socket.c:1890 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x61/0xcb Freed by task 6876: 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:362 __kasan_slab_free+0x11/0x20 mm/kasan/common.c:370 kasan_slab_free include/linux/kasan.h:220 [inline] slab_free_hook mm/slub.c:1600 [inline] slab_free_freelist_hook+0xc5/0x190 mm/slub.c:1626 slab_free mm/slub.c:3208 [inline] kfree+0xc0/0x270 mm/slub.c:4196 l2tp_session_free net/l2tp/l2tp_core.c:168 [inline] l2tp_session_put+0xb2/0x1a0 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+0x6fd/0xbc0 kernel/workqueue.c:2301 worker_thread+0xa8e/0x13c0 kernel/workqueue.c:2447 kthread+0x324/0x3b0 kernel/kthread.c:313 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:298 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 kernel/rcu/tree.c:2980 [inline] call_rcu+0x11a/0x1090 kernel/rcu/tree.c:3054 pppol2tp_release+0x1e3/0x2b0 net/l2tp/l2tp_ppp.c:447 __sock_release net/socket.c:597 [inline] sock_close+0xb8/0x200 net/socket.c:1286 __fput+0x2dc/0x730 fs/file_table.c:281 ____fput+0x15/0x20 fs/file_table.c:314 task_work_run+0x127/0x190 kernel/task_work.c:189 tracehook_notify_resume include/linux/tracehook.h:188 [inline] exit_to_user_mode_loop+0xcb/0xe0 kernel/entry/common.c:172 exit_to_user_mode_prepare+0x76/0xa0 kernel/entry/common.c:199 syscall_exit_to_user_mode+0x1d/0x40 kernel/entry/common.c:274 do_syscall_64+0x3d/0x40 arch/x86/entry/common.c:56 entry_SYSCALL_64_after_hwframe+0x61/0xcb The buggy address belongs to the object at ffff888125feac00 which belongs to the cache kmalloc-512 of size 512 The buggy address is located 400 bytes inside of 512-byte region [ffff888125feac00, ffff888125feae00) The buggy address belongs to the page: page:ffffea000497fa00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x125fe8 head:ffffea000497fa00 order:2 compound_mapcount:0 compound_pincount:0 flags: 0x4000000000010200(slab|head) raw: 4000000000010200 0000000000000000 0000000500000001 ffff888100043080 raw: 0000000000000000 0000000080100010 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 282, ts 23792990613, free_ts 0 set_page_owner include/linux/page_owner.h:35 [inline] post_alloc_hook mm/page_alloc.c:2456 [inline] prep_new_page+0x176/0x190 mm/page_alloc.c:2462 get_page_from_freelist+0x225f/0x23f0 mm/page_alloc.c:4254 __alloc_pages_nodemask+0x29a/0x640 mm/page_alloc.c:5384 alloc_slab_page mm/slub.c:-1 [inline] allocate_slab mm/slub.c:1813 [inline] new_slab+0x84/0x3f0 mm/slub.c:1874 new_slab_objects mm/slub.c:2632 [inline] ___slab_alloc+0x2f8/0x4c0 mm/slub.c:2796 __slab_alloc+0x63/0xa0 mm/slub.c:2836 slab_alloc_node mm/slub.c:2918 [inline] slab_alloc mm/slub.c:2960 [inline] __kmalloc_track_caller+0x1e4/0x310 mm/slub.c:4541 kmemdup+0x26/0x60 mm/util.c:131 ipv6_icmp_sysctl_init+0x2b/0x120 net/ipv6/icmp.c:1208 ipv6_sysctl_net_init+0x274/0x410 net/ipv6/sysctl_net_ipv6.c:221 ops_init+0x2c0/0x470 net/core/net_namespace.c:144 setup_net+0x34f/0xae0 net/core/net_namespace.c:345 copy_net_ns+0x314/0x520 net/core/net_namespace.c:486 create_new_namespaces+0x3a8/0x650 kernel/nsproxy.c:110 unshare_nsproxy_namespaces+0x120/0x170 kernel/nsproxy.c:231 ksys_unshare+0x4fa/0x820 kernel/fork.c:3156 page_owner free stack trace missing Memory state around the buggy address: ffff888125feac80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff888125fead00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >ffff888125fead80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff888125feae00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ffff888125feae80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ================================================================== ---------------- Code disassembly (best guess): 0: eb 23 jmp 0x25 2: e8 8f 0b 4e 00 call 0x4e0b96 7: e8 2a 26 e1 00 call 0xe12636 c: fa cli d: 65 48 8b 05 c1 38 ae mov %gs:0x7eae38c1(%rip),%rax # 0x7eae38d6 14: 7e 15: 4c 8b 30 mov (%rax),%r14 18: 41 f7 c6 0e 30 08 00 test $0x8300e,%r14d 1f: 0f 84 91 00 00 00 je 0xb6 25: fb sti 26: 41 f6 c6 08 test $0x8,%r14b * 2a: 74 05 je 0x31 <-- trapping instruction 2c: e8 65 61 2c 03 call 0x32c6196 31: 41 f7 c6 00 10 00 00 test $0x1000,%r14d 38: 74 08 je 0x42 3a: 48 89 df mov %rbx,%rdi 3d: e8 .byte 0xe8 3e: 14 49 adc $0x49,%al