================================================================== BUG: KASAN: use-after-free in hlist_unhashed include/linux/list.h:808 [inline] BUG: KASAN: use-after-free in hlist_del_init include/linux/list.h:865 [inline] BUG: KASAN: use-after-free in l2tp_tunnel_closeall net/l2tp/l2tp_core.c:1232 [inline] BUG: KASAN: use-after-free in l2tp_tunnel_del_work+0xcd/0x3d0 net/l2tp/l2tp_core.c:1273 Read of size 8 at addr ffff888125fa3480 by task kworker/u4:5/1059 CPU: 0 PID: 1059 Comm: kworker/u4:5 Not tainted syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026 Workqueue: l2tp l2tp_tunnel_del_work 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 hlist_unhashed include/linux/list.h:808 [inline] hlist_del_init include/linux/list.h:865 [inline] l2tp_tunnel_closeall net/l2tp/l2tp_core.c:1232 [inline] l2tp_tunnel_del_work+0xcd/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 Allocated by task 1050: 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:1867 [inline] __sys_connect+0x3ce/0x450 net/socket.c:1884 __do_sys_connect net/socket.c:1894 [inline] __se_sys_connect net/socket.c:1891 [inline] __x64_sys_connect+0x7a/0x90 net/socket.c:1891 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x61/0xcb Freed by task 1050: 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 pppol2tp_ioctl+0x748/0x960 net/l2tp/l2tp_ppp.c:-1 pppox_ioctl+0x1e4/0x320 drivers/net/ppp/pppox.c:93 sock_do_ioctl+0xda/0x380 net/socket.c:1068 sock_ioctl+0x472/0x740 net/socket.c:1208 vfs_ioctl fs/ioctl.c:48 [inline] __do_sys_ioctl fs/ioctl.c:753 [inline] __se_sys_ioctl+0x121/0x1a0 fs/ioctl.c:739 __x64_sys_ioctl+0x7b/0x90 fs/ioctl.c:739 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x61/0xcb 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 kvfree_call_rcu+0x117/0x670 kernel/rcu/tree.c:3539 drop_sysctl_table+0x2f5/0x430 fs/proc/proc_sysctl.c:1684 drop_sysctl_table+0x2e4/0x430 fs/proc/proc_sysctl.c:1687 unregister_sysctl_table+0x75/0x120 fs/proc/proc_sysctl.c:1722 unregister_net_sysctl_table+0x15/0x20 net/sysctl_net.c:127 neigh_sysctl_unregister+0x78/0x90 net/core/neighbour.c:3732 devinet_sysctl_unregister net/ipv4/devinet.c:2650 [inline] inetdev_destroy net/ipv4/devinet.c:326 [inline] inetdev_event+0x7df/0x1010 net/ipv4/devinet.c:1612 notifier_call_chain kernel/notifier.c:83 [inline] raw_notifier_call_chain+0x90/0x100 kernel/notifier.c:410 call_netdevice_notifiers_info net/core/dev.c:2052 [inline] call_netdevice_notifiers_extack net/core/dev.c:2064 [inline] call_netdevice_notifiers net/core/dev.c:2078 [inline] unregister_netdevice_many+0x100e/0x19f0 net/core/dev.c:10778 unregister_netdevice_queue+0x2e1/0x320 net/core/dev.c:10712 unregister_netdevice include/linux/netdevice.h:2937 [inline] __tun_detach+0xc9d/0x1450 drivers/net/tun.c:697 tun_detach drivers/net/tun.c:713 [inline] tun_chr_close+0x92/0x140 drivers/net/tun.c:3489 __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 ffff888125fa3400 which belongs to the cache kmalloc-512 of size 512 The buggy address is located 128 bytes inside of 512-byte region [ffff888125fa3400, ffff888125fa3600) The buggy address belongs to the page: page:ffffea000497e800 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x125fa0 head:ffffea000497e800 order:2 compound_mapcount:0 compound_pincount:0 flags: 0x4000000000010200(slab|head) raw: 4000000000010200 dead000000000100 dead000000000122 ffff888100043080 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 281, ts 19606528987, free_ts 19605519804 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 __kmalloc_reserve net/core/skbuff.c:144 [inline] __alloc_skb+0xdc/0x520 net/core/skbuff.c:212 alloc_skb include/linux/skbuff.h:1126 [inline] nlmsg_new include/net/netlink.h:953 [inline] inet_netconf_notify_devconf+0x169/0x220 net/ipv4/devinet.c:2120 __devinet_sysctl_register+0x31c/0x390 net/ipv4/devinet.c:2604 devinet_sysctl_register+0x169/0x1e0 net/ipv4/devinet.c:2638 inetdev_init+0x26c/0x490 net/ipv4/devinet.c:277 inetdev_event+0x1f4/0x1010 net/ipv4/devinet.c:1544 notifier_call_chain kernel/notifier.c:83 [inline] raw_notifier_call_chain+0x90/0x100 kernel/notifier.c:410 call_netdevice_notifiers_info net/core/dev.c:2052 [inline] call_netdevice_notifiers_extack net/core/dev.c:2064 [inline] call_netdevice_notifiers+0x119/0x190 net/core/dev.c:2078 register_netdevice+0x100a/0x13a0 net/core/dev.c:10098 page last free stack trace: reset_page_owner include/linux/page_owner.h:28 [inline] free_pages_prepare mm/page_alloc.c:1349 [inline] __free_pages_ok+0x80b/0x830 mm/page_alloc.c:1629 free_the_page mm/page_alloc.c:5445 [inline] __free_pages+0xd8/0x390 mm/page_alloc.c:5454 free_pages+0x82/0x90 mm/page_alloc.c:5465 __stack_depot_save+0x492/0x4c0 lib/stackdepot.c:359 kasan_save_stack mm/kasan/common.c:39 [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+0xe6/0x100 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] new_dir fs/proc/proc_sysctl.c:958 [inline] get_subdir fs/proc/proc_sysctl.c:1003 [inline] __register_sysctl_table+0xa35/0x1240 fs/proc/proc_sysctl.c:1352 register_net_sysctl+0x2c/0x40 net/sysctl_net.c:121 neigh_sysctl_register+0x9a9/0xa90 net/core/neighbour.c:3713 devinet_sysctl_register+0xaf/0x1e0 net/ipv4/devinet.c:2635 inetdev_init+0x26c/0x490 net/ipv4/devinet.c:277 inetdev_event+0x1f4/0x1010 net/ipv4/devinet.c:1544 notifier_call_chain kernel/notifier.c:83 [inline] raw_notifier_call_chain+0x90/0x100 kernel/notifier.c:410 call_netdevice_notifiers_info net/core/dev.c:2052 [inline] call_netdevice_notifiers_extack net/core/dev.c:2064 [inline] call_netdevice_notifiers+0x119/0x190 net/core/dev.c:2078 register_netdevice+0x100a/0x13a0 net/core/dev.c:10098 register_netdev+0x3e/0x50 net/core/dev.c:10191 Memory state around the buggy address: ffff888125fa3380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ffff888125fa3400: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >ffff888125fa3480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff888125fa3500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff888125fa3580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ================================================================== ------------[ cut here ]------------ refcount_t: underflow; use-after-free. WARNING: CPU: 0 PID: 1059 at lib/refcount.c:28 refcount_warn_saturate+0x120/0x1a0 lib/refcount.c:28 Modules linked in: CPU: 0 PID: 1059 Comm: kworker/u4:5 Tainted: G B W syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026 Workqueue: l2tp l2tp_tunnel_del_work RIP: 0010:refcount_warn_saturate+0x120/0x1a0 lib/refcount.c:28 Code: 04 01 48 c7 c7 60 4b 40 85 e8 1c ee 3a 02 0f 0b eb c3 e8 73 a8 26 ff c6 05 31 94 82 04 01 48 c7 c7 c0 4b 40 85 e8 00 ee 3a 02 <0f> 0b eb a7 e8 57 a8 26 ff c6 05 12 94 82 04 01 48 c7 c7 e0 4a 40 RSP: 0018:ffffc90000cd7c58 EFLAGS: 00010246 RAX: e7f48e7928f93300 RBX: 0000000000000003 RCX: ffff88810d7c8000 RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000 RBP: ffffc90000cd7c68 R08: ffff8881f7052fbf R09: 1ffff1103ee0a5f7 R10: dffffc0000000000 R11: ffffed103ee0a5f8 R12: ffff888125fa0020 R13: dffffc0000000000 R14: 0000000000000003 R15: 0000000000000000 FS: 0000000000000000(0000) GS:ffff8881f7000000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f5473065000 CR3: 000000011d5d5000 CR4: 00000000003506b0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: __refcount_sub_and_test include/linux/refcount.h:283 [inline] __refcount_dec_and_test include/linux/refcount.h:315 [inline] refcount_dec_and_test include/linux/refcount.h:333 [inline] l2tp_session_put+0xcb/0x1a0 net/l2tp/l2tp_core.c:192 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 ---[ end trace e3bedac4eb1a7353 ]---