================================================================== 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 ffff88812df28880 by task kworker/u4:1/9 CPU: 0 PID: 9 Comm: kworker/u4:1 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 7612: 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 7612: 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 The buggy address belongs to the object at ffff88812df28800 which belongs to the cache kmalloc-512 of size 512 The buggy address is located 128 bytes inside of 512-byte region [ffff88812df28800, ffff88812df28a00) The buggy address belongs to the page: page:ffffea0004b7ca00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x12df28 head:ffffea0004b7ca00 order:2 compound_mapcount:0 compound_pincount:0 flags: 0x4000000000010200(slab|head) raw: 4000000000010200 0000000000000000 0000000a00000001 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 0x1d2a20(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 15, ts 186840296424, free_ts 186720983446 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] ndisc_alloc_skb net/ipv6/ndisc.c:422 [inline] ndisc_send_ns+0x347/0xb10 net/ipv6/ndisc.c:631 addrconf_dad_work+0xa40/0x1480 net/ipv6/addrconf.c:4216 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 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_pcp_prepare mm/page_alloc.c:1421 [inline] free_unref_page_prepare+0x2b7/0x2d0 mm/page_alloc.c:3336 free_unref_page mm/page_alloc.c:3391 [inline] free_the_page mm/page_alloc.c:5443 [inline] __free_pages+0x146/0x390 mm/page_alloc.c:5454 free_pages+0x82/0x90 mm/page_alloc.c:5465 kasan_depopulate_vmalloc_pte+0x6b/0x90 mm/kasan/shadow.c:354 apply_to_pte_range mm/memory.c:2504 [inline] apply_to_pmd_range mm/memory.c:2540 [inline] apply_to_pud_range mm/memory.c:2568 [inline] apply_to_p4d_range mm/memory.c:2596 [inline] __apply_to_page_range+0x790/0xa20 mm/memory.c:2623 apply_to_existing_page_range+0x38/0x50 mm/memory.c:2874 kasan_release_vmalloc+0x97/0xb0 mm/kasan/shadow.c:464 __purge_vmap_area_lazy+0x1326/0x1440 mm/vmalloc.c:1382 _vm_unmap_aliases+0x2ec/0x370 mm/vmalloc.c:1779 vm_unmap_aliases+0x19/0x20 mm/vmalloc.c:1802 change_page_attr_set_clr+0x317/0xc10 arch/x86/mm/pat/set_memory.c:1732 change_page_attr_clear arch/x86/mm/pat/set_memory.c:1789 [inline] set_memory_ro+0x89/0xd0 arch/x86/mm/pat/set_memory.c:1935 bpf_jit_binary_lock_ro include/linux/filter.h:846 [inline] bpf_int_jit_compile+0x8473/0x8930 arch/x86/net/bpf_jit_comp.c:2134 bpf_prog_select_runtime+0x722/0x9c0 kernel/bpf/core.c:1876 bpf_prog_load+0x1031/0x14e0 kernel/bpf/syscall.c:2238 __do_sys_bpf kernel/bpf/syscall.c:4435 [inline] __se_sys_bpf+0x49a/0x740 kernel/bpf/syscall.c:4391 Memory state around the buggy address: ffff88812df28780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ffff88812df28800: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >ffff88812df28880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff88812df28900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff88812df28980: 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: 1 PID: 9 at lib/refcount.c:28 refcount_warn_saturate+0x120/0x1a0 lib/refcount.c:28 Modules linked in: CPU: 1 PID: 9 Comm: kworker/u4:1 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 40 4d 40 85 e8 ec 0e 3b 02 0f 0b eb c3 e8 63 a8 26 ff c6 05 81 8b 82 04 01 48 c7 c7 a0 4d 40 85 e8 d0 0e 3b 02 <0f> 0b eb a7 e8 47 a8 26 ff c6 05 62 8b 82 04 01 48 c7 c7 c0 4c 40 RSP: 0018:ffffc90000097c58 EFLAGS: 00010246 RAX: 83c873445434ad00 RBX: 0000000000000003 RCX: ffff88810024bb40 RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000 RBP: ffffc90000097c68 R08: ffff8881f7127453 R09: 1ffff1103ee24e8a R10: dffffc0000000000 R11: ffffed103ee24e8b R12: ffff88812df2b820 R13: dffffc0000000000 R14: 0000000000000003 R15: 0000000000000000 FS: 0000000000000000(0000) GS:ffff8881f7000000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00005555588ca908 CR3: 000000011d682000 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 6c8f626bfa1a7799 ]---